Car running hot?
Thread Starter
Skydog9
Joined: Sep 2020
Posts: 120
Car running hot?
I took my car on the Interstate for the first time since installing a water temp gauge. I have a Cutlass with 350 and Turbo 350 Trans. I recently installed a 180 degree Mr. Gasket thermostat. After getting up to speed on the freeway. Cruising at 70mph I noticed my temp steadily climbing above 180. The outside air temp is in the low to mid 70's.
Temp was right at 200 degrees. Being concerned, I got off the highway and on to the side streets. Temp started coming down right away. Pulled over and raised my hood to check the fan and see if I had any leaks. Fan was working as it should with no leaks visible. Running on the side streets at 45-50 mph the temp was still showing 185-190. From the reviews I read on the Mr. Gasket thermostat, I figured it would run at 180. Should I suspect the thermostat or something else?
Temp was right at 200 degrees. Being concerned, I got off the highway and on to the side streets. Temp started coming down right away. Pulled over and raised my hood to check the fan and see if I had any leaks. Fan was working as it should with no leaks visible. Running on the side streets at 45-50 mph the temp was still showing 185-190. From the reviews I read on the Mr. Gasket thermostat, I figured it would run at 180. Should I suspect the thermostat or something else?
Old(s) Fart
Joined: Mar 2007
Posts: 50,806
From: Northern VA
There's nothing wrong with your car. At 16 psi, your coolant boiling point is about 250 deg F. So long as the temp is stabilized at 200 and not continually creeping upward, you're fine. You might want to check A/F ratio during high speed cruise. Lean mixture can cause hot running. Keep in mind that E10 will be inherently leaner than straight gasoline with the same jetting.
Registered User
Joined: Feb 2013
Posts: 15,413
From: Phoenix, AZ
Do you know what the highway RPM is, or what rear gear ratio the car has?
Higher RPM obviously generates more heat, then slower speed (lower RPM) reduces the amount of heat generated so the coolant temp decreases.
So realistically, there may not be anything wrong at all. My car runs at 180 almost all the time, but on the highway at 3400 RPM during the summer the temp will creep upwards of 200. If I slow down to below 3000 RPM, the temp drops to 190-ish.
Higher RPM obviously generates more heat, then slower speed (lower RPM) reduces the amount of heat generated so the coolant temp decreases.
So realistically, there may not be anything wrong at all. My car runs at 180 almost all the time, but on the highway at 3400 RPM during the summer the temp will creep upwards of 200. If I slow down to below 3000 RPM, the temp drops to 190-ish.
Registered User
Joined: Oct 2015
Posts: 677
I took my car on the Interstate for the first time since installing a water temp gauge. I have a Cutlass with 350 and Turbo 350 Trans. I recently installed a 180 degree Mr. Gasket thermostat. After getting up to speed on the freeway. Cruising at 70mph I noticed my temp steadily climbing above 180. The outside air temp is in the low to mid 70's.
Temp was right at 200 degrees. Being concerned, I got off the highway and on to the side streets. Temp started coming down right away. Pulled over and raised my hood to check the fan and see if I had any leaks. Fan was working as it should with no leaks visible. Running on the side streets at 45-50 mph the temp was still showing 185-190. From the reviews I read on the Mr. Gasket thermostat, I figured it would run at 180. Should I suspect the thermostat or something else?
Temp was right at 200 degrees. Being concerned, I got off the highway and on to the side streets. Temp started coming down right away. Pulled over and raised my hood to check the fan and see if I had any leaks. Fan was working as it should with no leaks visible. Running on the side streets at 45-50 mph the temp was still showing 185-190. From the reviews I read on the Mr. Gasket thermostat, I figured it would run at 180. Should I suspect the thermostat or something else?
Extensive old thread but lots of good cooling info... in here:
https://classicoldsmobile.com/forums...e-heat-105434/
Thread Starter
Skydog9
Joined: Sep 2020
Posts: 120
I appreciate all the info. I do not have a tach so I do not know what rpm I am turning. The drivetrain is stock and I'm not sure of the gear ratio. I have not got the code off the axle to determine that yet. I know doing 70 mph with the three speed it is running faster than I like. Eventually I will upgrade to a 4 speed.
Barely Registered
Joined: Feb 2014
Posts: 2,636
From: Gillespie County, Republic of Texas
When I hear the term 4-speed used in that way, I think manual transmission. If you did mean 4-speed manual, that change will drop your top gear rpm only about 4% by eliminating torque converter slip.
'72 Cutlass ragtop
Joined: Jun 2016
Posts: 1,322
From: Tampa, FL
I'm here in Tampa and my 350/TH350 combo has the same characteristics - actually I'm also running a MRG 180 HP t-stat. Rest of my combo is a Cold Case aluminum rad, 7-blade GM fan, Milodon aluminum water pump and HD fan clutch... At highway speed, it runs up to about 190-195, drops back to 180 range under lower speeds and street cruising. I run approx 3k rpm per my in-dash tach at 70mph with 3.08 rear posi gears.
Last edited by 70sgeek; Feb 12, 2021 at 06:20 PM.
'72 Cutlass ragtop
Joined: Jun 2016
Posts: 1,322
From: Tampa, FL
the Parts Place repro clock/tach combo is a great drop-in piece, clock plugs into factory clock dash harness power connector and tach wire runs out thru firewall to distributor. - 10-minute install at most and I've had mine in place over 3 years with no accuracy or function issues.
If you've never replaced your factory rear diff, it maybe a standard 2.56 open
If you've never replaced your factory rear diff, it maybe a standard 2.56 open
Registered User
Joined: Sep 2006
Posts: 158
I took my car on the Interstate for the first time since installing a water temp gauge. I have a Cutlass with 350 and Turbo 350 Trans. I recently installed a 180 degree Mr. Gasket thermostat. After getting up to speed on the freeway. Cruising at 70mph I noticed my temp steadily climbing above 180. The outside air temp is in the low to mid 70's.
Temp was right at 200 degrees. Being concerned, I got off the highway and on to the side streets. Temp started coming down right away. Pulled over and raised my hood to check the fan and see if I had any leaks. Fan was working as it should with no leaks visible. Running on the side streets at 45-50 mph the temp was still showing 185-190. From the reviews I read on the Mr. Gasket thermostat, I figured it would run at 180. Should I suspect the thermostat or something else?
Temp was right at 200 degrees. Being concerned, I got off the highway and on to the side streets. Temp started coming down right away. Pulled over and raised my hood to check the fan and see if I had any leaks. Fan was working as it should with no leaks visible. Running on the side streets at 45-50 mph the temp was still showing 185-190. From the reviews I read on the Mr. Gasket thermostat, I figured it would run at 180. Should I suspect the thermostat or something else?
I had a mint 71 c/s, 350/350 with a 2.56. Bench with arm rest. Man, she was just a peach on the highway.
Thread Starter
Skydog9
Joined: Sep 2020
Posts: 120
Thanks for the headsup. I was unaware of the Parts Place. Checked out the TicToc tach. Only problem is I have PerTronix in my distributor. It mentions unless you have points or HEI, you need to contact the manufacturer for an adapter to lower the voltage. I'll have to look into it. My clock is not working. I like the fact that it fits into the the instrument panel.
'72 Cutlass ragtop
Joined: Jun 2016
Posts: 1,322
From: Tampa, FL
I have an MSD 8529 distributor, which I believe is essentially the same basic thing - 3-wire plug/play replacement for a standard distributor. I had a Pertronix distributor before, I recall the TTT worked fine - it was the Pertronix which was a piece of crap (other opinions may vary....)...
Out of Line, Everytime😉
Joined: Dec 2006
Posts: 10,116
From: Melville, Saskatchewan
I can tell you my tach worked fine with the Pertronix Ignitor 3 module in my HEI. Now getting a tach to work with my Mallory Hyfire 6AL has been a challenge. Even with adapters, no tach has worked with it. I just spent the extra for an Autometer tach, will know in a few days. Hopefully you got a good Mr Gasket high flow thermostat. Mine slowly started closing at speed, hard to diagnose when you have a consistently hot running motor and a new rad. At idle and low speeds, it flowed as it should. I wasn't the only one with this issue. As said, 200 is a walk in the park. Going to a Robert Shaw 180 high flow from a regular 195 thermostat kept my 350 below 200, 190 is the hottest it ran. Getting my 403 to run below 190 at any point was a challenge. It spent a lot of time in the 200 to 230 temperature range.
Thread Starter
Skydog9
Joined: Sep 2020
Posts: 120
The radiator looks clean. Good clean coolant, no bent fins inside the neck as far as I can see and no bent fins externally. I did buy the high flow 180 Mr. Gasket
thermostat. I had no idea that it would run hotter than what the thermostat is designed for. Now I know that I am running as expected. I did find the the code on my axle
and it is a standard 2.73 gear
thermostat. I had no idea that it would run hotter than what the thermostat is designed for. Now I know that I am running as expected. I did find the the code on my axle
and it is a standard 2.73 gear
Administrator
Joined: Oct 2009
Posts: 42,499
From: Poteau, Ok
That's not necessarily true, the thermostat is designed to run an engine at a minimum operating temperature which is close to what the rating is. The cooling system is what determines the maximum. Again the thermostat starts to open at the rated temp and may be fully open @5-15* over that.
Registered User
Joined: Feb 2013
Posts: 15,413
From: Phoenix, AZ
Norm, you are saying right there that the thermostat will open at a specific temperature. I am laughing as I type this.
Administrator
Joined: Oct 2009
Posts: 42,499
From: Poteau, Ok
Ok Norm, it actually does 2 things, it opens and closes. If your driving in sub-cold temperatures, the thermostat will begin to close if the engine falls below the rated temp raising the engine temp back up until it opens again to maintain the minimum operating engine temperature.
Administrator
Joined: Oct 2009
Posts: 42,499
From: Poteau, Ok
I completely understand both yours and Kenneth's comments. I remain unconvinced by your comments. The thermostat (device) is designed to perform one function, as I stated from the beginning:
If you elect to call the point where it opens a minimum temperature or a maximum temperature, that in my argument is immaterial. The thermostat remains as designed to perform one function
Thus far I am not dissuaded.
If I were to provide further commentary to previous comments, it would be to suggest the thermostat does nothing more than to "respond" to a particular temperature; which, remains the same - its design is to OPEN @ a particular temperature.
Finally, the thermostat has no considerations for temperatures or changes in temperature outside of its designed function. Whether it's sub-zero or 500°F - it does one thing only - its design is to OPEN @ a particular temperature. Again, if you elect to install a 100°F thermostat, 120°F, 180°F, 250°F, or 500°F thermostat it is designed to OPEN @ a particular temperature.
If you elect to call the point where it opens a minimum temperature or a maximum temperature, that in my argument is immaterial. The thermostat remains as designed to perform one function
Thus far I am not dissuaded.
If I were to provide further commentary to previous comments, it would be to suggest the thermostat does nothing more than to "respond" to a particular temperature; which, remains the same - its design is to OPEN @ a particular temperature.
Finally, the thermostat has no considerations for temperatures or changes in temperature outside of its designed function. Whether it's sub-zero or 500°F - it does one thing only - its design is to OPEN @ a particular temperature. Again, if you elect to install a 100°F thermostat, 120°F, 180°F, 250°F, or 500°F thermostat it is designed to OPEN @ a particular temperature.
Thread Starter
Skydog9
Joined: Sep 2020
Posts: 120
Appreciate all the discussion of the cooling system and the thermostats function. The main thing I got out of all the discussion is that the temp rating of the thermostat is not what the car's temperature is maintained at. It is all due to a properly functioning cooling system as a whole. I now know that 200-210 degrees at highway speeds is not abnormal.
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