tinner

I got my engine back together and have no more leaks. The engine is a built up 350. 9.8:1 compression, Comp XE284 cam, headers, 3:73 gears, etc... I have had some issues with it running hot in the past. Today was a 70 degree day and I took it for a short drive @60mph & 3000rpm. By the time I got back home the operating temp was 200 degrees. What is normal for this type of engine? Last year I sucked in the lower hose and thought that was the problem....I replaced it and would like a ballpark figure of what people are safely running. I have a 160 stat in it, new Ebay 3 core radiator. I have an autometer temp gauge in it too. I should probably check my timing. The distributor was recurved for the build. I was told that I should be able to time it to factory specs.....but it has an HEI would this change anything? Thanks!

MDchanic

If you have a 160° thermostat, then you should be at 160° on a 70° day.

Set your timing to about 34°-36° with the mechanical advance all in at about 3,000 RPM.

At idle, the HEI will probably be around 20°.

There are many threads on this subject here.

- Eric

m371961

You say you replaced the lower hose. Did you replace it with a hose that has a spring inside it?

tinner

I will have to borrow a good timing light from a friend. I didn't know if having the mods would do anything change the temp that it should be running at (Temp close to stat temp). I have an 18" mechanical fan on it. What is the hottest safe temp to run at that won't cause a problem?
I couldn't get a hose locally that had the spring in it....I tried. I ended up getting an ugly ribbed hose that won't collapse.

oldcutlass

Do you have a picture of the distance of the fan from the radiator? Do you have a shroud? Have you verified the accuracy of your temp gage.

Although 200 is not what I would call high, you may be able to get it a little lower.

jag1886

You have a new engine and you are running it a 3000RPM's, I could live with 200 degrees, the real question is was it stable at 200 or was it still climbing. I have about 2500 miles on my new engine now and when it is working hard it will run 200 on a 180 degree stat, but it run at 200 for hours and not go up any more. 200 is not to hot!

tinner

Ok, thanks for the responses. I value your opinions. The face of the fan is 4" away from the radiator. I am going on an assumption that my gauge is accurate, as it is a quality gauge. I did dig up a factory 18" fan & clutch from a '94 S-10 that I parted if you think this will help. I don't know if my temp stabilized at 200. I drove it three miles round trip after it was warmed up. The 18" fan gives me 1" clearance all the way around in my beat up shroud.

tinner

One more thing, if 200 degrees is acceptable....what isn't? Thanks!

M-14

94 s10 fan might be reverse rotation.
160 t stat will only be the minimum temp. You'd need lots of cold air blowing through the rad to run at that temp.

oldcutlass

Is that a flex o lite plastic fan? Do you not have a heater core?

My unacceptable is when the temp wont recover and keeps climbing above 210.

tinner

It's a plastic fan from jegs. I have a new heater core in it, but haven't hooked it up yet. I want to pick up a valve for it to shut it off if needed.

s i 442

I would replace the fan no matter what. You really can't beat a factory clutch fan. But if thats not an option then the bigger bladed flex fan would be better than what you got.
Also you only need about a half inch clearance all the way around from the fan to the shroud.

captjim

I have had a lot of experience with aftermarket radiators, especially cheap ones, not cooling properly. Less fins/sqare inch. I have a very similar set up and run a one row aluminum rad from a P series van. Inexpensive, works great.

captjim

I really don't understand this theory?? An open stat at 160 or 195 is the same size, so how does it matter. Once the stat opens, the engine should run close to that temp IF the rest of the system is up to par.

jag1886

You need to loose that plastic blade, the fan blades should be half in and half out of the shroud to work as efficiently as possible and if that S-10 fan came off a V6 it probably is reverse rotation, you also should repair that big hole in the shroud, that's like having a big hole in your tire.

oldcutlass

The stat sets minimum operating temp, it starts to open at the posted setting. The operating temp will be what it wants based on the efficiency of the system. In winter the 160 will limit the amount of heat you will get in the cabin. If the engine maintains close to the stat rating during cruise then the radiator is functioning correctly. If it keeps climbing past 205-210 at idle or in traffic, it's a fan issue.

Like captjim says, once they are open they don't do anything else unless the temp drops below the rating.

Yes, get a proper clutch fan setup or a better flex fan. Patch the hole in your shroud.

tinner

Thanks guys! It sounds like I have some more parts chasing. I will also have to see what I have stashed on the shelves.

1970-W30

I can understand this theory, removing the thermostat altogether would allow coolant to move thru the radiator way to fast before it could give up its heat, eventually overheating the engine. That's why thermostats even though they're 2 inches in diameter, only open with a bit less then a one inch diameter opening, allowing only a certain volume of coolant to flow thru them thereby controlling the rate of heat transfer as the coolant is going thru the radiator. The original factory design determined the size of the thermostat opening which in turn controls the flow rate thru the radiator for optimum cooling, I believe the thermostat temp rating has no effect on the volume/speed of coolant going thru the radiator, it just starts the process sooner or later depending on the temp rating of the stat.....
Just my 2 cents worth.

captjim

There is a LOT of bad information in the last 3 posts. I have this reputation as someone who "argues" because I feel the need to correct this bad info. I'm not going to do it again, maybe if someone else does, they will listen

The old "moves too fast to cool properly" is a myth

MDchanic

Yeah, I just don't have the time right now either, and I'm not a thermodynamic engineer, so it would take a while to come up with the source material, but basically, a radiator with a given efficiency of heat transfer from inside the tubes to the air, with a given amount of air flowing through it, at a given temperature gradient, should transfer heat from water to air at the same rate no matter how fast the water is flowing - each ounce of water that passes through may lose less heat as it moves faster, but the overall heat removed per unit time should be the same.

Like I said, no time now to dig up the equations.

- Eric

droldsmorland

Jeez were all real sorry you don't have the time for other than your 2 cents. Keep the change. Then why reply at all Einsteins. Keep the science out of the thread lets keep it real simple....Here it is in a nut shell try the dam higher temp stat if it works you win. If not call on the Einsteins

captjim

Interesting that you completely deleted your 2 posts which were absurd. The car overheated because the t-stat opened too soon?? The car overheated because the coolant moved too fast? THe car runs cooler with a higher stat? Really? YOU mention "thermodynamics" then deleted both posts. You are so confident that you are correct that as soon as the statement is challenged you delete them.

classicmuscle442

Just a thought, is the rubber piece still in place under the radiator in between the bumper?

tinner

I will have to take a look, but I believe most everything is intact. This car is a work in progress and needs alot more TLC than it did when I first owned it. I sure hope that these replies don't get as hot as my car. I just want the car to stay cool guys. I am taking your advice. I tried to source a new fan today (locally) which didn't work out, but will either order one or try and get to the bone yard that's further away on Saturday if I don't have my kids with me. I started to repair the shroud, which if I am lucky....I will get another one on Saturday (I guess he has alot of old cars at this one). I also will replace the stat. My housing is leaking anyway. After all of this, I will get a manual heater control valve & hook up my heater core until I have the time to hook up all of my vacuum lines that were removed by the previous owner. It's a work in progress, I just want to enjoy it.

MDchanic

I wish I had the full day or so that I would need to properly research this subject, find references from textbooks, and then write a comprehensible post about it, but I don't, so I won't.

I have, however, had the time to find a well-written and illustrated piece by somebody else, who does an excellent job of explaining the design and operation of automotive cooling systems, and also refutes the nonsensical suggestion that slower coolant flow improves cooling.

Read this, please, if you have the time.

Oh, and thanks for the compliment!



- Eric

steverw

So you say you just got it back together? Does that mean you rebuilt it, as in new rings, bearings, new internals? If so I think its normal for it to run a little hot as the tolerances are tighter until the motor is broken in. If that's the case give it a little time to let everything seat in and loosen up some....... perhaps it will then run cooler. If its not a new rebuild then disregard my post. I have always been told this of a fresh motor and it has been my experience of the motors I have built.

oldcutlass

Nice article. It explains a lot to people who are unfamiliar about cooling systems, designed engine operating temps, etc... I am not a proponent of electric fans or water pumps with old school engines in most circumstances though.

MDchanic

Yeah, but it at least explains why they can be helpful under certain circumstances.

Key point:
Heat flow increases with temperature gradient
(same thing applies to fluid flow [pressure gradient], current flow [voltage gradient], and molecular flow [concentration gradient]), which explains why it seems like the heat is pulled out of your house so much faster on a -10°F day than on a +20°F day.

As you increase flow through a radiator, inlet and outlet temperatures become closer together (the water leaving the radiator gets warmer).
This keeps the radiator temperature high, which keeps the temperature gradient high, which keeps the rate of heat transfer high.

Essentially, while the difference between inlet and outlet temperature will decrease as flow increases, both of those temperatures will decrease in real terms as well, so that while you initially had (and these are just hypothetical numbers), say, 220° into the radiator and 180° out, for a 40° difference with a slow flow, with a faster flow, you may have a 20° difference, but you will have 210° going into the radiator and 190° going out, meaning that the engine is now at 210° instead of 220°.

- Eric

1970-W30

Well Eric and captjim, I stand corrected and learned something new, 65 years old and still learning.

captjim

I hav also had issues with stock replacement stats, I think they can be restrictive. If you can, spend the extra $5 on as high flow stat (Moroso, RobertShaw), I think it is a good investment since you are replacing it anyway.

oldcutlass

I prefer the Stant SuperStat.

m371961

I am just throwing this out there, do not know if its right or not. Had a SBF stock car that did run hot without a thermo, restricted flow at thermo housing and all was well.
I was told at the time, if the flow was too fast the heat transfer from the engine to the coolant would be inefficent, the coolant moving too fast to absorb the heat. Who knows.

captjim

The science is indisputable. It is my understanding that the reason cars run hot without a stat is NOT the old "coolant moving too fast" deal but instead that the pump is designed with the restriction, so when you remove it, the pump can't keep up and cavitates.

1970-W30

Hold on here captjim, that doesn't make any sense, the thermostat is on the pressure side of the pump, how can the pump cavitate if it is presented with more coolant not less if the thermostat is removed? Cavitation happens when the intake volume of the water pump is restricted. According to Erics link article, there is plenty of back pressure resistance in the movement of coolant thru the heads and block with or without a thermostat that the pump has to overcome. I'm going to have to call BS on your "the pump can't keep up" statement.

MDchanic

I believe that the main reason for this has to do with pressure differentials between different areas of the cooling system.

The water tends to be pushed into the block by the pump, go through the block and heads, and leave the block through the thermostat, then into the radiator, across to the side with the radiator cap, and be sucked back into the pump.

In this system, the cap is in the area of lowest pressure, and just before the thermostat is the area of highest pressure.
Pressures just before the thermostat can be in the 40-50 psi range in a hot engine that is running fast.

The high pressure in the heads and the top of the engine help to keep the engine cool by preventing boiling at the surfaces, which improves heat transfer to the coolant and out through the radiator.
If you open up the restriction at the thermostat too much, the pressure head behind the thermostat can go down, which can reduce cooling efficiency - if the water is skating past the head surfaces on a cushion of steam, it won't pick up much heat and the engine will get hotter.

- Eric

1970-W30

That makes a lot more sense than the cavitating water pump theory......

captjim

You could be right, but that was what an engineer who designs cooling systems told me, but that doesn't make it correct.

MDchanic

I can see validity for the cavitation theory as well.

If the pump sees less of a pressure head, it will be more inclined to cavitate. Increasing the thermostat outlet size beyond design parameters could reduce the pressure that the impeller sees and lower the cavitation threshold, which will reduce pressures in the head more than just enlarging the thermostat opening, which will increase the likelihood of surface boiling, so it all works together.

Also note that in the cavitation scenario, enlarging the thermostat opening actually REDUCES the flow rate, which reduces cooling efficiency.

- Eric

1970-W30

Please explain how a reduction in head pressure induces cavitation? Lower head pressure does not induce cavitation on a pump, indequate inlet size or extreme inlet turbulance or pump intake restrictions can cause cavitation. As long as there is SOME head pressure, which there would be because of the engine cooling passages the coolant has to flow through, there will be no cavitation in the water pump. Will the pump volume increase as the head pressure goes down? Yes it will, but of all the reasons a thermostat should not be taken out, pump cavitation is not one of them.

captjim

Incorrect, again.

"The second issue is that of water pump cavitation and surge. Operated a pump at high RPM with insufficient head pressure provided by the frictional losses in the coolant passages and the thermostat creates a greater likelihood that the pump will either cavitate or surge. Cavitation is the condition where localized boiling or degassing occurs as the fluids exits the impeller vane and pressure changes."

From here,
http://www.flowkoolerwaterpumps.com/cooling_faq.html

No matter what I do, I end up "arguing". I suppose it is just better to let incorrect statements stand and all these internet myths can be perpetuated.