Help with engine running hot
Thread Starter
Pro
Joined: Oct 2011
Posts: 743
Likes: 71
From: Jarrettsville Maryland
Help with engine running hot
I have a 1979 Corvette with a DeWitts radiator, dual SPAL fans, timing set at 10 degrees. Whenever the A/C is turned on, the temperature climbs. If it's hot out, it will climb fairly high (it's gone over 220). If it's in the low 80's, it might climb up to 190. Turning on the A/C also turns on the fans.
It gets hottest while traveling at sustained high speeds. I took some IR readings today after a drive. I got 190* at the thermostat housing, 185* at the end of the upper radiator hose near the radiator, 165* at the top of the radiator by the upper radiator hose fitting. On the return side, I got anywhere from 160* at the top of the radiator on the passenger side, and as low as 125* towards the bottom.
HOWEVER, the lower radiator hose was reading just over 170*. This seems strange to me to have the coolant that's flowing back into the engine being hotter than the coolant in the radiator. I'm suspecting I might need a new water pump. What do the experts here think?
It gets hottest while traveling at sustained high speeds. I took some IR readings today after a drive. I got 190* at the thermostat housing, 185* at the end of the upper radiator hose near the radiator, 165* at the top of the radiator by the upper radiator hose fitting. On the return side, I got anywhere from 160* at the top of the radiator on the passenger side, and as low as 125* towards the bottom.
HOWEVER, the lower radiator hose was reading just over 170*. This seems strange to me to have the coolant that's flowing back into the engine being hotter than the coolant in the radiator. I'm suspecting I might need a new water pump. What do the experts here think?
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
make sure lower radiator hose isnt collapsing, should have a spring inside of it. i had to add a 2 inch extension to my lower air dam (spoiler) on my 79L82. i am running dual spals also. mine climbs some with the ac on but never over 200 degrees. i also have my timing set at 36 degrees total mech. advance, initial came out to 18. i am running straight manifold vacuum to the vacuum advance on the hei. timing helps alot with the temps.....running a 180 thermostat too.
Thread Starter
Pro
Joined: Oct 2011
Posts: 743
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From: Jarrettsville Maryland
make sure lower radiator hose isnt collapsing, should have a spring inside of it. i had to add a 2 inch extension to my lower air dam (spoiler) on my 79L82. i am running dual spals also. mine climbs some with the ac on but never over 200 degrees. i also have my timing set at 36 degrees total mech. advance, initial came out to 18. i am running straight manifold vacuum to the vacuum advance on the hei. timing helps alot with the temps.....
I've had the timing at a few degrees higher and lower, as well as disconnected the vacuum advance altogether, and none had any bearing on how hot the engine got.
The engine is built up with aluminum AFR heads and high compression pistons and has a complicated history since it was rebuilt.
EDIT: I'm running a 160* thermostat. I've tried 2 different ones with no change.
Thread Starter
Pro
Joined: Oct 2011
Posts: 743
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From: Jarrettsville Maryland
The IR temps were posted to show that the radiator is significantly colder than the coolant in the car, so airflow shouldn't be a problem. What is bothering me is that the lower radiator hose is hotter than the radiator, even though the coolant is supposed to flow from the radiator to the lower hose.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
You're reading the raw aluminum surface of the radiator vs a black hose right? The emissivity difference between the materials could easily explain it.
http://www.engineeringtoolbox.com/em...nts-d_447.html
You won't get a proper temperature reading from materials with low emissivity like aluminum using an IR gun calibrated for a material with a relatively high emissivity like almost anything that is black. Paint the radiator tank black where you're reading temperature and try it again.
http://www.engineeringtoolbox.com/em...nts-d_447.html
You won't get a proper temperature reading from materials with low emissivity like aluminum using an IR gun calibrated for a material with a relatively high emissivity like almost anything that is black. Paint the radiator tank black where you're reading temperature and try it again.
Thread Starter
Pro
Joined: Oct 2011
Posts: 743
Likes: 71
From: Jarrettsville Maryland
You're reading the raw aluminum surface of the radiator vs a black hose right? The emissivity difference between the materials could easily explain it.
http://www.engineeringtoolbox.com/em...nts-d_447.html
You won't get a proper temperature reading from materials with low emissivity like aluminum using an IR gun calibrated for a material with a relatively high emissivity like almost anything that is black. Paint the radiator tank black where you're reading temperature and try it again.
http://www.engineeringtoolbox.com/em...nts-d_447.html
You won't get a proper temperature reading from materials with low emissivity like aluminum using an IR gun calibrated for a material with a relatively high emissivity like almost anything that is black. Paint the radiator tank black where you're reading temperature and try it again.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
The dual fans could actually restrict the air coming thru the radiator at cruising speeds. Duntov was aware of how much the shroud would reduce the air flow thru the radiator at high speeds and I'm suspecting that is what is happening to yours.
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Burning Brakes
Joined: May 2014
Posts: 1,094
Likes: 16
From: Los Angeles California
do you have front spoiler or air deflector in place. are your seals around raddy in place. do both fans turn on when it reaches set temp. I had a similar problem and one of the fuses was installed incorrectly and 2nd fan wouldn't turn on but I had more trouble while stuck in LA traffic and it would run 220 on hw but wouldn't climb up, once I got both fans running good I barely see 210.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
You mentioned your initial timing as 10* BTDC which is generally a good place to start. Where is it at RPM? Point being are you sure your advance is working?
Next thing was the heads were changed, did you do it? Any pics of the process? Are you sure all the passage holes lined up?
I know you probably did this but make sure the fans are pulling air through the radiator. Got any pics of the setup? Is the radiator sealed to the mount? On my 81 there are a couple plastic pieces connected to the front of the fender skirts that seal that area up, make sure those are in place.
As stated above, Air Dam in place and in the correct shape?
Next thing was the heads were changed, did you do it? Any pics of the process? Are you sure all the passage holes lined up?
I know you probably did this but make sure the fans are pulling air through the radiator. Got any pics of the setup? Is the radiator sealed to the mount? On my 81 there are a couple plastic pieces connected to the front of the fender skirts that seal that area up, make sure those are in place.
As stated above, Air Dam in place and in the correct shape?
Thread Starter
Pro
Joined: Oct 2011
Posts: 743
Likes: 71
From: Jarrettsville Maryland
You mentioned your initial timing as 10* BTDC which is generally a good place to start. Where is it at RPM? Point being are you sure your advance is working?
Next thing was the heads were changed, did you do it? Any pics of the process? Are you sure all the passage holes lined up?
I know you probably did this but make sure the fans are pulling air through the radiator. Got any pics of the setup? Is the radiator sealed to the mount? On my 81 there are a couple plastic pieces connected to the front of the fender skirts that seal that area up, make sure those are in place.
As stated above, Air Dam in place and in the correct shape?
Next thing was the heads were changed, did you do it? Any pics of the process? Are you sure all the passage holes lined up?
I know you probably did this but make sure the fans are pulling air through the radiator. Got any pics of the setup? Is the radiator sealed to the mount? On my 81 there are a couple plastic pieces connected to the front of the fender skirts that seal that area up, make sure those are in place.
As stated above, Air Dam in place and in the correct shape?
I didn't replace the heads. At some point between January and April, all of the coolant in my car disappeared without any signs of overheating or leaking. That trashed the heads. They were replaced by the engine builder with the same heads that came off of it.
Fans are definitely pulling air, both fans are coming on at temperature and because of the ac.
The front air dam is in place.
Radiator seals around the top of the radiator are missing, but they've always been missing and it didn't even start to get hot before.
The main thing that I'm concerned about is the fact that the return hose is hotter than the radiator. I may just replace the hoses since they're cheap.
Melting Slicks
Joined: Feb 2006
Posts: 3,105
Likes: 96
From: Sunrise FL
More timing advance=less heat generated. Hook up the vac advance up.
And use the seal at top of rad. This is VERY needed to keep air thru the rad, not AROUND it at speed. I made mine using a 2 in foam for a window AC from HD.
And use the seal at top of rad. This is VERY needed to keep air thru the rad, not AROUND it at speed. I made mine using a 2 in foam for a window AC from HD.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
ALL seals around the radiator are VERY important. You need to keep in mind that you want to isolate the area in FRONT of the fan/radiator from the motor compartment as much as possible.
You have a great setup and it should be able to keep up with no problem. Of course, I am biased as I have the same setup and it never overheats.
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Joined: Oct 2011
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From: Jarrettsville Maryland
Racer
Joined: Jul 2013
Posts: 307
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From: Kirkland WA
You mentioned this started after getting new AFR heads. What kind of headers are you using and did you do a port match?
If the header flange is covering any portion of the head exhaust port there will be a flow inversion and a build up of heat in the head. I didn't see in your posts, but do you also have temperature measurements taken there?
Last edited by Silvertone; Sep 16, 2015 at 01:32 PM.
Thread Starter
Pro
Joined: Oct 2011
Posts: 743
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From: Jarrettsville Maryland
You mentioned this started after getting new AFR heads. What kind of headers are you using and did you do a port match?
If the header flange is covering any portion of the head exhaust port there will be a flow inversion and a build up of heat in the head. I didn't see in your posts, but do you also have temperature measurements taken there?
If the header flange is covering any portion of the head exhaust port there will be a flow inversion and a build up of heat in the head. I didn't see in your posts, but do you also have temperature measurements taken there?