Heating up at idle
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Instructor
Joined: Jul 2007
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Heating up at idle
I have a 72 sb that is newly rebuilt basicly stock except 9.5 :1 comp.
New water pump, t-stat and new Dewit oem replacement rad. The car maintains 180 while driving but when it sits at idle the temp climbs untill I start moving. The fan clutch seems ok. What else could cause the temp to come up that fast at Idle. Out side temps in the low 80's
New water pump, t-stat and new Dewit oem replacement rad. The car maintains 180 while driving but when it sits at idle the temp climbs untill I start moving. The fan clutch seems ok. What else could cause the temp to come up that fast at Idle. Out side temps in the low 80's
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Heating up at idle is usually an indication of a faulty fan clutch. You should not be running hot with a Dewitt's radiator. As others have suggested, confirm your timing, temp (with IR gun) and that you have the correct vacuum can.
Drifting
Joined: May 2008
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From: Choctaw Country
Burning Brakes
Joined: Oct 2001
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From: TN
full time
two terms full time vacuum and ported vacuum. Check and see what your vacuum advance is getting at idle. At idle, remove the vacuum hose at the vacuum advance unit. If the idle drops and you can feel vacuum when you put your finger over the line, you have full time vacuum. Full time vacuum helps your engine run cooler at idle and in stop and go traffic plus you get better gas mileage. If you increase the the rpms and the carb blades open and you get vacuum, this is ported vacuum.
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From: mount holly NC
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Clutch fan test.
A basic test to see if the clutch fan it working is to start a cold engine run it for 2 minutes and shut if off. See how much resitance it takes to turn the fan by hand, then run the motor for 10 minutes and check the resistance again, it should now be harder to turn. PG.
Safety Car
Joined: Mar 2007
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From: Bridgewater nj
You can also wait until it starts heating up again and check it. The fan should have a firm drag on it when turned. unlike when its cold you can get it to spin 1 rotation if you fling it. If it spins more than one rotation cold it is bad from the get go.
Race Director
Joined: May 2006
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From: Dayton, Ohio
Put your hand in front or radiator and feel for good air flow.
If you put a shop towel on the front of the radiator the air flow should hold it there.
A good fan clutch will ROAR off and on at idle.
Sometimes if you put a fan in front of the car you can add to the flow...if this extra air flow does help, the fan clutch is most likely bad.
If you go looking for a fan clutch GM #88981768 wont let you down.This sucker has the ability to move so much air that it adds 10mph to the top speed of the car.
If you put a shop towel on the front of the radiator the air flow should hold it there.
A good fan clutch will ROAR off and on at idle.
Sometimes if you put a fan in front of the car you can add to the flow...if this extra air flow does help, the fan clutch is most likely bad.
If you go looking for a fan clutch GM #88981768 wont let you down.This sucker has the ability to move so much air that it adds 10mph to the top speed of the car.
Racer
Joined: Jul 2004
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From: Mesa az
Back to Basics
I have to ask the "basics". Do you feel a good air flow coming through the radiator into the engine compartment at idle? Is the fan mounted correctly (not backwards)? Is the shroud complete without missing pieces/sides? Is the fan positioned inside the shroud? Are all the shroud-to-radiator, radiator-to-support air seals in place? Are you running your AC if you have it (shouldn't hurt, but would be interesting)? Have you cleaned out the AC condensor/radiator so air flows freely?
Drifting
Joined: Aug 2008
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How hot does it run? Running hotter at idle than moving down the road at 65 or so is an indication of not enough air flow. By moving you are creating the needed air flow. The GM service manual will tell you to run the engine up to operating temp and watch the fan as you shut the engine off. If it makes more than 2 revolutions it is defective. Also, if the engine is cold, give the fan a good spin with your hand, again, if it makes more than 2 revolutions it is bad. For a good read on this go the Hayden Clutch Fan website, they also outline the troubleshooting procedure very well. As far as your vac advance is concerned, don't be overly concerned. The amount of cooling it adds at idle is minimal at best. New engines will have a tad more friction and some will run a little warmer than others. Again, how hot is hot - 200, 210? If the engine runs smooth and pulls strong your probably looking at an air flow issue.
Safety Car
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From: Austin Texas
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"The car maintains 180 while driving,
but when it sits at idle the temp climbs untill I start moving"
This tells me your getting enough heat transfer from your system,
when you have enough Air CFM flowing(when you move).
You need better CFM , this means either your not sealed around the radiator,
or your fan is not pulling the CFM needed..
If your radiator is sealed, and the correct Fan....replace the clutch.
69VETT
but when it sits at idle the temp climbs untill I start moving"
This tells me your getting enough heat transfer from your system,
when you have enough Air CFM flowing(when you move).
You need better CFM , this means either your not sealed around the radiator,
or your fan is not pulling the CFM needed..
If your radiator is sealed, and the correct Fan....replace the clutch.
69VETT
Le Mans Master
Joined: Apr 2004
Posts: 7,106
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From: Newark DE
idle and low speed driving cooling issues are usually caused by:
1. bad fan clutch
2. incorrect timing
3. incorrect vacuum advance set-up
to check the fan clutch bring motor up to full operating temp and shut motor down. Fan should stop within 1-3 revolutions. if it takes significantly longer or just free spins it's bad and needs replacement
double check your timing. Initial timing should be in the 10º-15º range on a basically stock motor with the vacuum advance hose disconnected from the vac adv can and the hose plugged.
To check your vacuum advance, first pull the hose off the carb nipple to check if it's on full manifold vacuum or ported vacuum. If the idle speed drops and you can feel vacuum on the carb nipple it's full manifold vacuum (the preferred connection). If the idle doesn't change and you feel no vacuum at idle on the carb nipple it's on a ported connection and you want to move it to a full manifold vacuum source.
Reconnect the vac adv hose and recheck the initial timing. It should be 15º-16º above the initial timing you have previously with the vac adv disconnected. If it's not you are not pulling enough vacuum advance into your timing, effectively retarding it which can cause an increase in operating temps.
1. bad fan clutch
2. incorrect timing
3. incorrect vacuum advance set-up
to check the fan clutch bring motor up to full operating temp and shut motor down. Fan should stop within 1-3 revolutions. if it takes significantly longer or just free spins it's bad and needs replacement
double check your timing. Initial timing should be in the 10º-15º range on a basically stock motor with the vacuum advance hose disconnected from the vac adv can and the hose plugged.
To check your vacuum advance, first pull the hose off the carb nipple to check if it's on full manifold vacuum or ported vacuum. If the idle speed drops and you can feel vacuum on the carb nipple it's full manifold vacuum (the preferred connection). If the idle doesn't change and you feel no vacuum at idle on the carb nipple it's on a ported connection and you want to move it to a full manifold vacuum source.
Reconnect the vac adv hose and recheck the initial timing. It should be 15º-16º above the initial timing you have previously with the vac adv disconnected. If it's not you are not pulling enough vacuum advance into your timing, effectively retarding it which can cause an increase in operating temps.
Thread Starter
Instructor
Joined: Jul 2007
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This is great Info. I will check the seals again. The temp at idle steadly climbs although I never let it get to high as I just start driving it and it coms down again. Everthing is new or rebuilt except the fan clutch and that seem ok. The only thing is the seals but they don't seem as though they could make that much of a diference. As far as timing my machine shop that did my motor work put my distributer on his machine and said if I had 12 degrees of initial timing it will give me 36 degrees total at around 2500 rpm(which it does). He also said plug the vacume lines and run it without vacume advance. Not sure why|!
Safety Car
Joined: Oct 2007
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From: Austin Texas
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the Seals around the Radiator = think of it like this
" sip any drink thru a straw,...now put a small hole in it."
Notice any difference?"
without the seals, the fan will pull air around the fan,
Instead of thru it, Which is exactly what you don't want.
Good Luck...69VETT
" sip any drink thru a straw,...now put a small hole in it."
Notice any difference?"
without the seals, the fan will pull air around the fan,
Instead of thru it, Which is exactly what you don't want.
Good Luck...69VETT
Drifting
Joined: Aug 2008
Posts: 1,381
Likes: 11
You should run a functional vacuum advance, but do not be so quick to used full manifold vacuum vs ported vacuum. Some engine combos run better with ported vs manifold vacuum. If you are running a camshaft that is slightly larger than stock and an automatic trans it will have a tendency to drop the rpm or even die when placed in gear. This is because the engine suddenly has a load placed on it by the trans. When this happens, rpm decreases and vacuum falls off, decreasing your timing as well, resulting in insufficient idle speed. Ported vacuum allows you to run a little more cam and not suffer the rpm drop when placed in gear. You can also hear the cam alot better because the it's not being covered up with advanced timing. Once the throttle is opened you get your advanced timing from the port and everything is equal to the manifold method.
