225 running a bit warm!!!

-
stimac0000@hotmail.com

[email protected]

Active Member
Joined
Jan 31, 2011
Messages
28
Reaction score
0
Location
Missouri
Hey my slant six runs at 201 Degrees with a 180 thermostat and if I'm on the highway if running about 75 mph a bit higher like 215 or so but if I let off the gas it goes back down just wondering is this normal or what? I have a new thermostat, radiatior, water pump, checked for small leaks nothing that is out of the norm. hoses seem good to, even added water wetter. Temps been close to the 100,s here in MO lately!!!
 
well i would say some things up with it check and check some more mine runs 160 to 170 on the hot days i cant think of any thing off hand to help ya good luck bud
 
If it's an auto use a trans cooler. Try a different thermostat. Tighten the belt. Recheck temp with a different gauge, in case you are getting a bad reading.
 
High-speed overheating = insufficient water flow. Low speed/stuck-in-traffic overheating = insufficient airflow. Both kinds of overheating at the same time = both problems together with probable buildup of rust and crud in the engine's coolant passages and/or a radiator, no matter how clean, that has too much solder junction corrosion to do its job effectively. Don't try masking the problem with a lower-temperature thermostat...find the problem and fix it.
 
A lower temp thermostat usually causes the vehicle to run hotter. A higher temp thermostat will lower engine temps.

When lower temp is used the coolant in the radiator doesn't have enough time to cool down. When a higher temp is used the radiator gets cooler thereby lowering your engine temp.
 
oneway71 said:
A lower temp thermostat usually causes the vehicle to run hotter. A higher temp thermostat will lower engine temps.

When lower temp is used the coolant in the radiator doesn't have enough time to cool down. When a higher temp is used the radiator gets cooler thereby lowering your engine temp.
Click to expand...

uhhh, not sure where your at, but down here in Texas a lower degree thermostat most definitely reduces the operating temperature. If your cooling system is up to par, the radiator has plenty of time to cool off between cycles when using a lower thermostat.

FYI One of the most common GM EFI tricks is to run a lower thermostat to keep the engine running cooler so that the computer can run a more aggressive timing curve.
 
Ok so what temp themostat should I use a 190? Slant Six Dan if there is rust and crud in the block how do you tell for sure and how do you fix it? with a coolant flush or???
 
is 21 degrees over the thermostat rating really that bad in ambient temps ~90° to 100°?
 
I know you said the hoses looked good, but you need to make sure one of them isn't collapsing. A 180 thermostat is ok, but if it is stuck it would cause your problem. I've had many new ones that did not work properly, so now I test them in hot water to see if they function before installing them. Did you do anything else to this car we don't know about? Like maybe advance the timing too far?
 
streetdak said:
uhhh, not sure where your at, but down here in Texas a lower degree thermostat most definitely reduces the operating temperature. If your cooling system is up to par, the radiator has plenty of time to cool off between cycles when using a lower thermostat.

FYI One of the most common GM EFI tricks is to run a lower thermostat to keep the engine running cooler so that the computer can run a more aggressive timing curve.
Click to expand...

I should have added the line that said this is being taught at current college level ASE classes.
 
Check for any leaks, loose rad cap etc. Any loss of pressure will cause it to run hotter.
 
If it is a flow issue then removing the thermostat may help but I wouldn't recommend it for more than just a test period. Remember that thermostats are there to keep your car from running too cold, not too hot.

I would try the following:
Back-flush and put some kind of cleaner in the system.

and

Check your spark-plugs. if you are running rich or lean you will overheat.
Run a can carb medic through the carb.

and

Make sure your EGR valve is not stuck shut.
 
Looks like you have a few hints so far. I'd first make sure the t-stat is working correctly and timing is set to specs as magnumdart mentioned. Actually, it's retarded timing that causes overheating unless you advance it so far it's pinging all the time. Check for vacuum leaks or other reasons for a lean air/fuel ratio condition as that will contribute to hot running at all speeds. Another cause that I've seen (and you won't want to hear) is an engine with a bad core shift that gets overbored. If the cylinder walls are too thin in areas, you'll never get it to run cool as the coolant boils right in the block before it has a chance to get cooled. Good luck!
 
trapster said:
If it is a flow issue then removing the thermostat may help but I wouldn't recommend it for more than just a test period. Remember that thermostats are there to keep your car from running too cold, not too hot.

I would try the following:
Back-flush and put some kind of cleaner in the system.

and

Check your spark-plugs. if you are running rich or lean you will overheat.
Run a can carb medic through the carb.

and

Make sure your EGR valve is not stuck shut.
Click to expand...
Not completely true. In some systems, it will overheat without a thermostat in place. If the coolant flows too freely, there is poor heat transfer to the radiator/air. Rich running won't cause an overheat problem.
 
Years ago my 225 was overheating and it was caused by 2 problems. Since I was rebuilding the head anyway and had it off I poked a screwdriver into the rear cylinder water jacket and got nothing but rusty mush. I cleaned it and flushed it all out and I had the radiator boiled and cleaned at the same time. After putting the engine back together it never got hot even on the hottest days. In retrospect, I probably should have boiled the block but they would have been a lot more work and expense.
 
cudamark said:
Not completely true. In some systems, it will overheat without a thermostat in place. If the coolant flows too freely, there is poor heat transfer to the radiator/air. Rich running won't cause an overheat problem.
Click to expand...

Yes but we were assuming that we are not getting enough flow here :)
 
If the radiator and/or block is plugged, pulling the thermostat won't help.
 
Wow thanks guys lots of ideas I am going to try some of them this weekend!!! My motor is a 1971 225 so there is no egr valve, I dont know if anyones been inside the motor to bore it out but could be I didnt think of it being bored with thinner cylinder walls. It is forty years old so anything is possible I guess!!! oh hey one more thing I have a none clutch solid steel race 17inch 6 blade fan with no shroud would that do it?
 
I have a suggestion that no one else here suggested and it sounds simple but can't hurt to check that there is enough coolant to water. I had my head rebuilt and the mechanic apparently left my radiator not full I added a gallon before it topped off and I ran hot in an idle situation.
 
Sorry I meant Manifold heat control valve could be stuck shut ? If you still have one.

Just backflush it and use some kind of radiator cleaner.

Clean out your Carb jets with a can of Carb medic. And see what happens.
 
I saw the pic of your car with no shroud and thought about it. It could help at slower speeds for sure, and wouldn't hurt at higher speed. By the way, what is the condition of the anti-freeze? Is it still clean? If it is dirty already you could try a backflush of the block. Also, if there is too much anti-freeze and not enough water it could get hot, as anti-freeze alone or in too high a concentration transfers heat poorly.
 
The coolant is 50/50 and I added a bottle of water wetter. The coolant looks clean no real reason to think its rusted and mucked up. Maybe I will change the hoses this weekend and backflush the block its a start I guess. In that pic there was a noisy flex fan steel with aluminum blades tossed it and put the solid steel race fan on it!!! Simply for noise reduction!!! Once again thanks guys for helping me troubleshoot this!!!
 
I'm not sure what you mean by a "solid steel race fan" but most low resistant fans don't pull enough air. Your problem, however, seems to be water flow.....not air flow. If you can, post a photo of it so we can start another debate! You might try putting your flex fan on it just for diagnostic purposes. If it cures the problem, get a new fan similar in size but with solid blades, not a flex fan....those things can grenade on you. On a different subject.....are you related to a Craig Stimac that used to play pro baseball?
 
You must log in or register to reply here.
-

Back
Top