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Olds 455 that is 0.60 over, iron heads, 4 core aluminum radiator, shroud and fan all in proper working order.
I currently have the 180F t-stat and the engine runs around 190-200F but can get to 210F sitting in traffic and when shutdown, it can heat-sink to like 220F. (Summer driving). I've noticed that most 455 engines will run usually 10-20 degrees ABOVE the t-stat temp and another 10F when in traffic during summer.
I will be re-installing the 160F t-stat for summer driving. I noticed when I had the 160F t-stat years ago, the engine would run 170-180F and then about 190F when in traffic and would heat-sink to 200F after hot shutdown. The engine made more power with the 160F t-stat and ran cooler. Overall engine compartment temps were lower and it was less prone to pinging if fuel octane wasn't up to par.
Dyno runs also showed more HP was made when coolant temps were 170-180F vs 190F-200F. These 455 engines with iron heads don't dissipate heat as quickly as those running aluminum heads.
Once the t-stat opens, the size of the radiator is what controls the engine temp. If your engine is running 190-210 now at steady state, changing to a 160 thermostat will have zero effect on that.
When driving down the highway the engine temp goes to 180F and never drops below that. The t-stat prevents it from cooling below 180F.
Once the 160F is installed. My engine temps drop to 160F down the highway. I know this to be true as when I had the 160F installed. My engine temp would drop to 160F once on the highway. Off the highway it would them stay at 170-180F. I know this to be true as that's what it ran before I did the switch.
So I would have to disagree with you as that's what it ran before the switch. The 180F t-stat prevents it from cooling below 180F. Even when it can and would with the 160F t stat. Just like 200F tstat will prevent the engine from ever getting below 200F. Even if you had the best cooling system in the world. It would never drop below 200F when driving.
Last edited by pettrix; June 25th, 2019 at 05:30 PM.
I never said that the t-stat won't change the low end temp if your low temp is the t-stat set point. Your first post said that the engine was running 190-210 with a 180 t-stat, which says that the t-stat is fully open. If that is true, the lower t-stat won't change that. The mind reading isn't working. I can only comment on the information that you post. And frankly, why do you want the engine to run below 180? All that does is hurt fuel atomization and change engine internal clearances.
A 455 will typically run around 10-20 degrees ABOVE what the t-stat is. On a properly operating cooling system. So a 200F t-stat will make the engine run 210-220F, probably hotter when in traffic. A 180F t-stat will run 190-200F. A 160F t-stat will run 170-180F.
The above is considering driving in avg traffic with summer temps in the 80s-90. Once you introduce 90F+ outside temps, heavier traffic, the operating temps will increase by 10 degrees.
Once the 160F is installed. My engine temps dropped to 160F down the highway. I know this to be true as when I had the 160F installed. My engine temp would drop to 160F once on the highway. Off the highway it would them stay at 170-180F range.
Why would one run the engine to run 180? Because on a 455 engine that's .60 over, the 455's already had poorly designed and thin cylinder walls. Running it hot doesn't help these design defect. Why would you want detonation?
I have yet to see a 455 blow a head gasket because coolant temps were too low. I have seen plenty 455's blow a head gasket when temps get too hot.
What "internal clearances" are you taking about? Oil temp is not the same as coolant temp.
Ask anyone who races 455's and they will tell you. Keep the coolant temp low and the oil hot. The engine will run the best. 455's run best when coolant temps are 180F or lower.
Last edited by pettrix; June 25th, 2019 at 05:38 PM.
Other than the fact that your fan isn’t providing enough cooling air, not sure if there’s a question in there. Fan clutch might not be keeping up. I’d also make sure you have plenty of base timing and consider using manifold vacuum advance, the timing helps with heat at low speeds. I run a 160F in everything, except the 440 cuda doesn’t have a thermostat and runs really cold. Seems to like it.
A thermostat controls the minimum operating temperature of the engine. Typically they start to open around the rated temp but could take +/- up to 15* of the rated temp to fully open. 180*-200 is not too hot for an engine and will not cause detonation because of operating temp.
I have run a 160 thermostat in my car for years, it usually runs around 170-175 normally. Back when I drove the car year round I would step up to a 180 in the winter so I’d have heat. I did get caught in a early cold snap in my college days, I don’t think the engine ever got above 130. I was cold!! I put some cardboard in front of the radiator, that helped. Damn cold Indiana/Ohio winters!!
A thermostat controls the minimum operating temperature of the engine. Typically they start to open at the rated temp and may fully open +/- up to 15* of that. 180*-200 is not too hot for an engine and will not cause detonation because of operating temp.
CORRECT !
My 455 runs best at 185+
Below 180... Dog.
160 was part of the Royal Bobcat Tune up. I use one as well, on my buddy’s 70 Z, a 160 wasn’t letting the choke work, I’m not convinced the thermo temp doesn’t matter, mine runs too cool in the fall.
The airflow you get going down the highway at 60-70 mph is pretty intense and no clutch fan is going to produce that type of airflow as highway driving would.
A high-performance 455 will run hotter than a stock 455. A 0.60 over bored cylinder will tend to run hotter than a .30 over or stock bored cylinder.
If the cooling system is up to par. A 160F t-stat will typically make the engine run 170-180F in moderate traffic and heat and 190F in heavier traffic and heat.
455s don't come with knock sensors and if the compression is hovering around 10:1, you can detonate, especially if running hotter.
Your chart references dynamic not static compression, big differences. Engines are designed to run in the 200-210 degree range. In fact the viscosity ratings on engine oils are all based on the engine being in that 200-210 degree range. The thermostat will have nothing to do with that temperature. That, as Joe stated, is determined by the radiator.
Your chart references dynamic not static compression, big differences. Engines are designed to run in the 200-210 degree range. In fact the viscosity ratings on engine oils are all based on the engine being in that 200-210 degree range. The thermostat will have nothing to do with that temperature. That, as Joe stated, is determined by the radiator.
When you say "engines" are you referring to every single engine produced? The Olds 455 engine? GM engines? Chrysler, Ford engines?
Each manufacturer has their own specs. Not all engines are created alike and some like to run cooler than others and some like to run hotter.
Dyno runs on the 455 with iron heads always showed me that they like to run in the 180F range for peak HP. Once it hits 190F, the HP #s drop. Once it hits the 210F range, HP drops even more and detonation begins on higher compression engines. That's a 455. Not all engines respond the same to temps. Modern Chevy LS aluminum engines like 200-210F for peak HP but they are aluminum and are engineered TOTALLY different than a 455.
Joe is wrong.
Last edited by pettrix; June 27th, 2019 at 08:24 AM.
Joe never said anything about operating temps vs. HP output. Go read my posts again.
My ONLY statement was that once the thermostat is open, it has ZERO effect on coolant temp. Only the radiator sizing determines temp at that point (for a given engine).
Joe never said anything about operating temps vs. HP output. Go read my posts again.
My ONLY statement was that once the thermostat is open, it has ZERO effect on coolant temp. Only the radiator sizing determines temp at that point (for a given engine).
The t-stat controls coolant temp to the effect that it will PREVENT the coolant from dropping below a certain temp. A 180F t-stat will PREVENT the coolant temp from dropping BELOW 180F once the car is at operating temps. So while cruising down the highway, with tons of airflow, the coolant will not drop below 180F due to the 180F t-stat. With a 200F t-stat, the coolant will never drop below 200F on the highway.
With a 160F t-stat, the coolant temp will drop to 160F while on the highway. The engine oil temp will be around 215F.
The t-stat controls coolant temp to the effect that it will PREVENT the coolant from dropping below a certain temp. A 180F t-stat will PREVENT the coolant temp from dropping BELOW 180F once the car is at operating temps. So while cruising down the highway, with tons of airflow, the coolant will not drop below 180F due to the 180F t-stat. With a 200F t-stat, the coolant will never drop below 200F on the highway.
With a 160F t-stat, the coolant temp will drop to 160F while on the highway. The engine oil temp will be around 215F.
No one is arguing that. Go read the posts again. The OP said his car was running 190-210 on the freeway. At that point, both a 160 and a 180 t-stat is fully open. The steady state temp at that point is governed by the radiator sizing. This is not a difficult concept to grasp. If the car is running 190 plus with a 180 t-stat, installing a 160 t-stat is NOT going to lower that.
No one is arguing that. Go read the posts again. The OP said his car was running 190-210 on the freeway. At that point, both a 160 and a 180 t-stat is fully open. The steady state temp at that point is governed by the radiator sizing. This is not a difficult concept to grasp. If the car is running 190 plus with a 180 t-stat, installing a 160 t-stat is NOT going to lower that.
Maybe he is just trying to buy another 30 seconds of time before it get to hot, lol
No one is arguing that. Go read the posts again. The OP said his car was running 190-210 on the freeway. At that point, both a 160 and a 180 t-stat is fully open. The steady state temp at that point is governed by the radiator sizing. This is not a difficult concept to grasp. If the car is running 190 plus with a 180 t-stat, installing a 160 t-stat is NOT going to lower that.
I don't have the read the post again because I wrote it. The OP (me) did NOT say I was running 190-210 on the freeway. I never said that. Here, let me quote myself:
Originally Posted by pettrix
When driving down the highway the engine temp goes to 180F and never drops below that. The t-stat prevents it from cooling below 180F.
Once the 160F is installed. My engine temps drop to 160F down the highway. I know this to be true as when I had the 160F installed. My engine temp would drop to 160F once on the highway. Off the highway it would then stay at 170-180F. I know this to be true as that's what it ran before I did the switch.
I don't have the read the post again because I wrote it. The OP (me) did NOT say I was running 190-210 on the freeway. I never said that. Here, let me quote myself:
From the first post:
I currently have the 180F t-stat and the engine runs around 190-200F but can get to 210F
Frankly, I don't care if it's on the freeway or at idle. Please explain how if the engine is already at 190, changing the t-stat from 180 to 160 will lower that. But hey, knock yourself out...
Frankly, I don't care if it's on the freeway or at idle. Please explain how if the engine is already at 190, changing the t-stat from 180 to 160 will lower that. But hey, knock yourself out...
You might not care but the coolant and facts do care. As I stated a dozen times already. The engine will run around 10 degrees HOTTER than the t-stat when in city driving. So a 180F t-stat will run 190F, a 160F t-stat will run 170F.
On the highway, with the 60-70mph wind flow, the engine will run right above the t-stat temps. So a 180F t-stat will run just above 180F, a 160F t-stat will run just above 160F.
Simple concept but if you just want to argue for arguments sake, go ahead...
X2 Pettrix- In the past folks commented my 30 over 455 in my 67 442 resto mod running to cool. It had Edelbrocks, Torker,( plenty of Aluminum) M21 4 speed and an particular year Suburban aluminum ( sold the car about 4 years ago) that fit right in with no mods. That motor in Texas heat never ran over 180-190 degrees, in the fall 165-170 tops. That said, I got away with more timing and that car ran very well and was extremely reliable. Works for me.
Olds 455 that is 0.60 over, iron heads, 4 core aluminum radiator, shroud and fan all in proper working order.
I currently have the 180F t-stat and the engine runs around 190-200F but can get to 210F sitting in traffic and when shutdown, it can heat-sink to like 220F. (Summer driving). I've noticed that most 455 engines will run usually 10-20 degrees ABOVE the t-stat temp and another 10F when in traffic during summer.
I will be re-installing the 160F t-stat for summer driving. I noticed when I had the 160F t-stat years ago, the engine would run 170-180F and then about 190F when in traffic and would heat-sink to 200F after hot shutdown. The engine made more power with the 160F t-stat and ran cooler. Overall engine compartment temps were lower and it was less prone to pinging if fuel octane wasn't up to par.
Dyno runs also showed more HP was made when coolant temps were 170-180F vs 190F-200F. These 455 engines with iron heads don't dissipate heat as quickly as those running aluminum heads.
So was there a question here...? The trade off of higher HP at lower temps is higher engine wear.
X2 Pettrix- In the past folks commented my 30 over 455 in my 67 442 resto mod running to cool. It had Edelbrocks, Torker,( plenty of Aluminum) M21 4 speed and an particular year Suburban aluminum ( sold the car about 4 years ago) that fit right in with no mods. That motor in Texas heat never ran over 180-190 degrees, in the fall 165-170 tops. That said, I got away with more timing and that car ran very well and was extremely reliable. Works for me.
Thanks! Nice motor!
There are 2 school of thoughts on this. The old school purists who think that 210F is the best operating temp since that is what the factory set the range at. Then there is the modifiers and racers who build these motors, race them, and know what works to get the best performance out of them.
The 200F+ guys are running stock cast iron exhaust manifolds because that's how the factory ran them.
The unproven but often repeated "the engine will wear faster if you run it below 200F" which again is nonsense and doesn't apply to 455s. Each engine responds differently to coolant temps. 455's with their thin cylinder walls and not the best head clamping design (blown head gaskets), don't perform the best when running temps in the 200F+ range. Any performance builders know that one runs the oil hot and engine cool to get the best performance. 455's like the 170-180F spot. You can get away with more timing at those temps. With aluminum heads you can go maybe 190F but probably still fall back at 180F as the sweet spot.
I have an oil temp gauge and I run 210-220F on the oil temp once warmed up on the road. Even with a 160F t-stat.
Last edited by pettrix; June 27th, 2019 at 11:04 PM.
Swapped out the 180F t-stat for the 160F Robert Shaw t-stat last night and tested it. Engine coolant ran 165-170F on the highway (55-65mph) and ran 175-180F in city stop and go traffic. Definitely runs cooler now.
Just from a common sense standpoint......if the thermostat is fully open, like Joe says, the operating temperature is dictated by the efficacy of the cooling system since all the thermostat does is inhibit coolant flow to reach a minimum operating temp. That being true.....if you have a 180 degree thermostat that works as it should if your car reaches 200 degrees...regardless of how it got there (highway, in traffic or sitting in the garage doing the Macarena), a 160 thermostat won't make a difference. Again, at 200 degrees the thermostat is going to be fully open.....what temperature it popped open at really doesn't make a difference.
Put another way......if the thermostat was the primary determining factor of what temp the engine runs at, then why all the discussion about radiators and the other associated bits and pieces of the cooling system? If all I had to do was pop in a 160 degree thermostat to lower my operating temperature....well, Hells Bells man! Why didn't you guys say so before? (perhaps because it simply isn't true?)
Put a third way...as there seems to be conflicting posts by the OP......if you have a 180 thermostat and you switch to a 160 and run at 160-175 max....you should never have seen temps above 180 in the first place.
As far as what temp is best for the motor.......I gotta think that the guys at GM might have had some idea of what they were doing. If I recall, the assembly book I looked at showed a 195 degree thermostat being what came from the factory so 210ish degree operating temps really shouldn't be out of the question so this may all be moot point anyway...
That said, if it blows your hair back.....it's all good in the neighborhood.
Cheers,
Troy
Last edited by troyd; June 28th, 2019 at 01:01 PM.
I gotta think that the guys at GM might have had some idea of what they were doing. If I recall, the assembly book I looked at showed a 195 degree thermostat being what came from the factory so 210ish degree operating temps really shouldn't be out of the question so this may all be moot point anyway...
I guess the "guys" at GM knew what they were doing when they installed 2 bolt mains on a long stroke engine and put a 4 quart oil pan on the 455. They then designed the engine to send all the oil up the top end and starve the bottom end of oil so you can spin a main or rod bearing under WOT conditions. What a "great design" if you want your 455 engine to become a grenade.
Reality is that the 455 in stock form was a botched design that needed much improvement.
So the same logic applies to your 195F t-stat comment. If you think running 210F+ is good for performance and longevity on a 455, then you don't race or have a HP 455.
How about the botched W27 aluminum differential that would blow up under full throttle conditions? That was a design disaster and while a "rare" option it is not sought after in racing circles as it's a weak and problematic differntial design. Most people go with a Ford 9" or a GM Chevy 12 Bolt differential. How about the Olds diesel block from the 1980's. A boat anchor from day 1.
Last edited by pettrix; June 28th, 2019 at 03:35 PM.
No real interest in engaging in a Urinary Olympiad with someone who doesn't really understand the purpose and function of a thermostat.......while I will grant you that not all engineers are perfect and that Detriot peddled a LOT of garbage (a point well made)....but the properties of thermodynamics are not all that complicated and probably pretty well understood by those folks.
However, good for you that you got a big stash of vintage Hot Rod mags to entertain yourself with. Perhaps an old Sears catalog and you can entertain yourself until Labor Day.......
Some people like to think they know more than they do.
A few salient thermodynamic and fluid mechanics points need to be made here.
1. A radiator's efficiency is, all other factors being the same, dependent on the temperature gradient between it and ambient. This means three things, firstly, the colder it is outside, the more cooling the radiator will do. Secondly, the hotter the fluid going into the radiator, the more cooling it will do on a given day. Thirdly, this means that, eventually, that radiator will match the heat output of the engine, it just may be above the operating limits of the system (boiling point of ethylene glycol water mix under pressure, as in 250 deg F).
2. A thermostat is a flow restrictor both actively and passively. It blocks some flow when open, and all flow when closed. (some as opposed to it not being there)
3. A proper cooling system, seen on new cars, has a radiator that will beat engine heat load always, and it regulates it with the thermostat opening and closing and a fairly imprecise gauge.
4. Many old cars exceed the capacity of the thermostat to regulate the system. The radiator cannot cool the engine and keep it at that temp, at that load, and it must rise in temperature until it is capable of matching the thermal load (see the first point). This is why cars "run hot" but not boil over.
5. Performance thermostats open sooner, and flow higher volume, so some extra cooling is achieved, both steady state (more flow) and changing state (the car is starting from colder, and will both rise to temp slower, and lose temp faster once load changes).
I have achieved some system performance in a Chevy of mine by taking the original 190 deg low emissions stock thermostat and putting in a 160 deg performance stat. The increased thermal reservoir of it being colder when not under high load, being able to cool off faster due to increased flow, and not
get as high under steady state operation due to increased flow, have taken some 20 deg off the temp at all times. It does not beat a clean radiator, which is next.
Many good points made, and several that are flat-out wrong. The trick is to recognize which is which.
Newer cars run hotter than older ones, largely due to emissions requirements. It's been said that modern fan clutches are tuned to engage ten or fifteen degrees "hotter" than the OEM clutches from the '60s.
Thermostat rating AND fan-engagement rating (clutch or electric) both affect engine temperature. GM doesn't even turn on the electric fan until 210. Secondary fan on my Lumina engages at 220, I think.
Even the '60s cars had "HOT" warning lights that didn't light up until 240--260 degrees. Engine damage at low-200s is not an issue. The issue is how much above thermostat rating should the engine run DURING IDLE AND CRUISE (i.e., all light-throttle driving. Let's say 1/4 throttle and less.)
I get upset if the engine is more than 10 degrees above thermostat rating at idle or cruise (keeping in mind the engagement point of the fan clutch or electric fan.) At 15--20 degrees above thermostat rating, the thermostat has LOST CONTROL of the engine temperature, and that should not happen at idle or cruise, at least with a direct-driven rad fan.
***The ENTIRE POINT of the thermostat is to variably REDUCE the efficiency of the cooling system, because the cooling system is sized to deal with medium-throttle applications and would over-cool at light throttle. If you're running with the thermostat fully open at light throttle, there's no reserve capacity for heavier-throttle operation.***
HEAVY-throttle engine operation is a whole different thing. Automotive radiators are NOT sized to provide cooling during long-term WFO operation, which is why the temperature climbs. Look at the size of semi-tractor or bus or even 2-ton farm truck radiators. They're HUGE. For that matter, consider the Chevy "TRUCK" 366 and 427 (based on the Big Block Chevy engine, but reinforced for heavy-throttle use) thermostat housings--they look like a "**** and *****" because there's TWO thermostats underneath, and a rad hose thats double the size of typical automotive stuff--because it takes a LOT of coolant flow when there's heavy throttle use, and trucks often run WFO for hours at a time. I bet the radiator is four times the size of a "big" automotive rad.
The old rule-of-thumb is "overheating when stopped or low speed is too little cooling air movement. Overheating at high speed is too little coolant flow." I find this is usually but not always true. There's too many instances of poor engine tune, missing OEM air ducting equipment (shrouds, under-radiator air dams, cowl seals at the rear of the hood, etc.) and just plain failed radiators--plugged water tubes, corroded or plugged air fins, etc. I see folks bitching about the fan clutch when the real problem is the air fins on the radiator. The radiator can't transfer heat to the air, so the fan clutch never sees the high temperature air it needs to engage.
Last edited by Schurkey; July 13th, 2019 at 08:28 PM.
I see a lot of opinions on this issue on the internet, and a lot of it I'm not expert enough to really follow too well. But in my experimenting with an 80's 350, I note one thing that is never mentioned. If you have the emissions devices still set up, the temperature can be critical to switching the tvs switches on the manifold which control these things. Those vacuum switches are set at 180 degrees. It is common for one of them to actually control the vacuum advance if it is attached to manifold vacuum, and the other controls an efe valve. This routes hot exhaust gases to the base of the carburetor for cold starts. That is deactivated at 180 degrees. If you are running a 160 or 180 stat and these connections are still there, you might have issues relating to the fact that these vacuum switches will not activate. That may be one of the reasons OEM is 195. For full emissions set up `195 is probably required. Of course it wouldn't apply to older cars without those conditions. But something to consider.
Food for thought...what is the coolant/water ratio? Was more straight coolant added after changing the intake and thermostat? Has the ambient air temp increased much since the swap?
The good news/ bottom line is those temps aren't concerning other than that there was an unexplained temp increase after the repair.
This conversation is now getting interesting to me, as I have been trying to understand the way the Engineers designed the engine around 55 years ago for my 1969 Cutlass Supreme with the 350 engine. Twenty three years ago I switched the original 195° thermostat to a 180° thermostat. My thinking at that time was the thermostat was that hot because it was the beginning of the emission era and that they wanted to meet emissions. At that time I had read switching to a 180° would help preserve the rubber components under my hood and help avoid pre-detonation. I had not had my car for that long then so I never noticed how my choke worked. On my engine the choke is a divorced coil that is built into the intake. Shortly after I changed to the 180° thermostat I noticed my choke never seem to be open as tight as I liked. When I asked the mechanic that set my mixture screws on the carb he said it was working correctly and I took his word for it. Recently after talking to a friend I realized the choke was set up for a 195° thermostat, that's when I started researching more on the subject. When going through my books, I noticed Oldsmobile had been using the 195° thermostat starting with the 330 cubic inch engine back in 1964. I then realized the Oldsmobile Engineers made it that temperature for something else than emissions and I would like to find out why. To quote Joe Padavano when someone rags on the turkey tray, Oldsmobile Engineers have spent more time designing that gasket than any other gasket and usually the problems with the turkey tray are because people don't understand how to install it right. I assume that the Engineers know more about what the engine temperature should be and so now I have switched back to the 195° thermostat. I am currently trying to sort out the Holley Sniper fuel injection system I just installed, so I don't have a lot of testing on the 195° thermostat. Other than the fuel injection, my engine is all original and has never been apart. It has 10.25:1 compression and has the original cam, intake, exhaust manifolds, and cooling system with all the radiator skirting and shrouds. I have not had it on the highway yet, but in town with 90° plus days the temperature has to gotten above 205° usually though it runs at 200° or slightly below. If anybody has any thoughts on why Oldsmobile Engineers used a 195° thermostat, I would like to hear about it.
I think you're looking at something incorrectly. The choke is heated by the exhaust crossover gases, and not the engine coolant. The 15ºF temperature difference in coolant between a 180º or 195ºF thermostat would be in the noise compared to the 1000ºF+ exhaust gases.
June 25th, 2019, 03:34 PM
