[C2] Engine overheating after rebuild
Thread Starter
Instructor
Joined: Feb 2023
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Engine overheating after rebuild
Help please with an overheating issue. Here are the details.
I just had my 67 mechanically restored. I purchased a date correct 427/390 block bored .70 over that was sonic tested. The engine was rebuilt to spec using all date correct OE parts.
The radiator is original, but I had a new core put in it and flow tested. All new hoses too. Also, the water pump is original and I had it rebuilt too. New thermostat as well, using a 180.
So, the car starts on the first try and does not leak at all. After 20 minutes the temp slowly starts to climb from 210-220-230 then into the yellow which is when I shut it down. The radiator then boils over and escapes through the overflow hose. I replaced the thermostat and repeated the same process and got the same result.
The radiator fluid is a 50/50 mix and the fan shroud doesn't have any gaps on the sides. My restorer and I can’t figure out what next to try. We are thinking buy a new off the shelf water pump and see if that works, then a new radiator. Problem is I have an original radiator and spent $750 to have a new core put in.
Any ideas on what could be causing this would be very appreciated.
Thank you,
Rex
I just had my 67 mechanically restored. I purchased a date correct 427/390 block bored .70 over that was sonic tested. The engine was rebuilt to spec using all date correct OE parts.
The radiator is original, but I had a new core put in it and flow tested. All new hoses too. Also, the water pump is original and I had it rebuilt too. New thermostat as well, using a 180.
So, the car starts on the first try and does not leak at all. After 20 minutes the temp slowly starts to climb from 210-220-230 then into the yellow which is when I shut it down. The radiator then boils over and escapes through the overflow hose. I replaced the thermostat and repeated the same process and got the same result.
The radiator fluid is a 50/50 mix and the fan shroud doesn't have any gaps on the sides. My restorer and I can’t figure out what next to try. We are thinking buy a new off the shelf water pump and see if that works, then a new radiator. Problem is I have an original radiator and spent $750 to have a new core put in.
Any ideas on what could be causing this would be very appreciated.
Thank you,
Rex
Burning Brakes
Joined: Jan 2021
Posts: 1,027
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From: Pittsburgh area
Did you boil the thermostat first to see if it actually opens before install?
Also, once started with cap off I'd check to see if the anti-freeze is actually flowing
not just rising up and down.
Could be that rebuilt pump, as well as other issues.
GL
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Also, once started with cap off I'd check to see if the anti-freeze is actually flowing
not just rising up and down.
Could be that rebuilt pump, as well as other issues.
GL
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Six decades strong!
93 Vette
74 Capri MK1
Team Owner
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From: Sitting in his Nowhere land Hanover Pa
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with a IR gun what does it say?
then read this:
camaros.org/pdf/corv_cooling2.pdf
camaros.org/pdf/timing101.pdf
then read this:
camaros.org/pdf/corv_cooling2.pdf
camaros.org/pdf/timing101.pdf
Race Director
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I've recently seen a buddy go through several T-stats that didn't work before one acted right. As mentioned...ck it in a pan of water. Or run without it for a test. A rebuilt water pump can introduce issues if they used a different impeller or didn't set it at the correct height.
How about fan clutch? Is it really locking in when it's hot? Is it the type with an exposed coil on the front? Fan clutches have a whole range of operating temps depending on who made them.
Have you checked with an I/R gun to verify that's the real temps?
What's the timing curve? How much initial and vacuum and total mechanical? Advanced timing will cool things down.
JIM
How about fan clutch? Is it really locking in when it's hot? Is it the type with an exposed coil on the front? Fan clutches have a whole range of operating temps depending on who made them.
Have you checked with an I/R gun to verify that's the real temps?
What's the timing curve? How much initial and vacuum and total mechanical? Advanced timing will cool things down.
JIM
Thread Starter
Instructor
Joined: Feb 2023
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GL,
No we didn’t boil the thermostat, just bought another one. Probably should have. I’ll
try and start the car with the cap off and see if it does flow. Another person asked about the fan clutch. It is 23 years old, so it might be bad. I’m
probably going to order a new one.
Thanks for the advice.
Cheers,
Rex
Thread Starter
Instructor
Joined: Feb 2023
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I've recently seen a buddy go through several T-stats that didn't work before one acted right. As mentioned...ck it in a pan of water. Or run without it for a test. A rebuilt water pump can introduce issues if they used a different impeller or didn't set it at the correct height.
How about fan clutch? Is it really locking in when it's hot? Is it the type with an exposed coil on the front? Fan clutches have a whole range of operating temps depending on who made them.
Have you checked with an I/R gun to verify that's the real temps?
What's the timing curve? How much initial and vacuum and total mechanical? Advanced timing will cool things down.
JIM
How about fan clutch? Is it really locking in when it's hot? Is it the type with an exposed coil on the front? Fan clutches have a whole range of operating temps depending on who made them.
Have you checked with an I/R gun to verify that's the real temps?
What's the timing curve? How much initial and vacuum and total mechanical? Advanced timing will cool things down.
JIM
Great ideas. I’ll boil one or both of the thermostats and see if they open at 180. No I don’t believe my restorer used an IR gun to see the temp, but I will inform him.
We are looking at replacing the Fan clutch because it is the only thing that hasn’t been replaced.
As far as the water pump rebuild goes, I don’t know. The guy is very reputable so I would assume he got it right, but again I’m
assuming.
I’ll get after these things and let you know.
Cheers,
Rex
Le Mans Master
Joined: Jan 2007
Posts: 6,003
Likes: 1,509
From: Prescott Arizona
Hey Rex - Good to hear you've been making progress on your 67, even if there are a few hiccups along the way.
If I recall correctly, when you inherited your Dad's 67 L36 Roadster, you found some things that prevented you from 'just firing it up'.
So, it's not like items such as the clutch fan had a good bill of health before you tore into an engine rebuild, so it might or might not be the problem.
I think you used the folks down in the Phoenix area to rebuild your original water pump, yes? ChevyCool, I think is the name? If so, they seem to have a good reputation.
Maybe you could enlighten us a bit on some of the details such as was this the initial startup, meaning you were breaking in the engine and it was 'in' the garage, not being driven with airflow through the radiator?
How about your initial timing setting and is the vacuum advance disconnected when it's being checked? Not sure but maybe the 67 L36 VAC configuration might be connected to ported vacuum,
not manifold vacuum, so no real difference (at idle) when you reconnect it. No vacuum leaks you're aware of when this overheating happened?
Mike T - Prescott AZ
If I recall correctly, when you inherited your Dad's 67 L36 Roadster, you found some things that prevented you from 'just firing it up'.
So, it's not like items such as the clutch fan had a good bill of health before you tore into an engine rebuild, so it might or might not be the problem.
I think you used the folks down in the Phoenix area to rebuild your original water pump, yes? ChevyCool, I think is the name? If so, they seem to have a good reputation.
Maybe you could enlighten us a bit on some of the details such as was this the initial startup, meaning you were breaking in the engine and it was 'in' the garage, not being driven with airflow through the radiator?
How about your initial timing setting and is the vacuum advance disconnected when it's being checked? Not sure but maybe the 67 L36 VAC configuration might be connected to ported vacuum,
not manifold vacuum, so no real difference (at idle) when you reconnect it. No vacuum leaks you're aware of when this overheating happened?
Mike T - Prescott AZ
Last edited by Vet65te; Nov 1, 2023 at 10:17 AM.
Drifting
Joined: Dec 2014
Posts: 1,756
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From: Chantilly Virginia
My "don't try this at home" test for fan clutches to wait till is should be fully engaged then stick a bundle of rolled up newspaper into it. If you get confetti, it's good. If it stops rotating it's bad. YMMV
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Melting Slicks
Joined: Jul 2004
Posts: 2,452
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From: Scottsdale AZ
When you pressure test. Does it hold?
Also you can run the engine with the pressure gauge on it. And see if it holds steady or climbs and climbs.
Also you can run the engine with the pressure gauge on it. And see if it holds steady or climbs and climbs.
Last edited by John S 1961; Nov 1, 2023 at 12:50 PM.
Safety Car
Joined: Nov 2001
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From: northern CA
It sounds like your problem could be the radiator. A freshly rebuilt over bored engine will run hotter during the break in period. You mentioned the radiator was redone with a new core which would suggest it is a copper/brass unit. Compared to an aluminum radiator, a copper/brass radiator loses 20-25% of cooling capacity in comparison. It would seem the radiator in your '67 doesn't have enough cooling margin to reject the extra heat the engine is producing.
John
John
Drifting
Joined: Jul 2007
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From: homosassa florida
A rebuilt engine will run HOT but at some point it will run cooler-timing would be a start you could put a high speed blower in front of the car before removing the fan and see it it helps. Also drill a small hole in the t-stat to allow no air build up.
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Instructor
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Gentlemen thank you for all your helpful replies. The timing is set to 6 degrees advanced and the spec is 6-8. We did check the pressure of the radiator cap and it was good. After reading everyone’s post, I suspect it to be a combination of a new motor being bored 70 over and break in, compounded by my radiator. I think I’ll buy an off the shelf radiator and see if it runs cooler. If that fixes the problem, I will break the car in with it and then swap them out afterwards. Hopefully that fixes the problem.
Sorry I can’t reply to individual messages, busy with Halloween for the kids and going to the World Series tonight. Go Rangers!
Cheers,
Rex
Sorry I can’t reply to individual messages, busy with Halloween for the kids and going to the World Series tonight. Go Rangers!
Cheers,
Rex
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If you're buying any radiator make sure it's a Dewitt's aluminum one. They are not cheap. But either is your car
Le Mans Master
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From: Temple Terrace Florida
Have you driven the car on the highway yet? If it's within normal limits on the highway, that would point to a fan clutch problem. A picture of your cooling system would be of help to determine if the seals and shroud are installed properly. Jerry
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Melting Slicks
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From: Scottsdale AZ
Help please with an overheating issue. Here are the details.
I just had my 67 mechanically restored. I purchased a date correct 427/390 block bored .70 over that was sonic tested. The engine was rebuilt to spec using all date correct OE parts.
The radiator is original, but I had a new core put in it and flow tested. All new hoses too. Also, the water pump is original and I had it rebuilt too. New thermostat as well, using a 180.
So, the car starts on the first try and does not leak at all. After 20 minutes the temp slowly starts to climb from 210-220-230 then into the yellow which is when I shut it down. The radiator then boils over and escapes through the overflow hose. I replaced the thermostat and repeated the same process and got the same result.
The radiator fluid is a 50/50 mix and the fan shroud doesn't have any gaps on the sides. My restorer and I can’t figure out what next to try. We are thinking buy a new off the shelf water pump and see if that works, then a new radiator. Problem is I have an original radiator and spent $750 to have a new core put in.
Any ideas on what could be causing this would be very appreciated.
Thank you,
Rex
I just had my 67 mechanically restored. I purchased a date correct 427/390 block bored .70 over that was sonic tested. The engine was rebuilt to spec using all date correct OE parts.
The radiator is original, but I had a new core put in it and flow tested. All new hoses too. Also, the water pump is original and I had it rebuilt too. New thermostat as well, using a 180.
So, the car starts on the first try and does not leak at all. After 20 minutes the temp slowly starts to climb from 210-220-230 then into the yellow which is when I shut it down. The radiator then boils over and escapes through the overflow hose. I replaced the thermostat and repeated the same process and got the same result.
The radiator fluid is a 50/50 mix and the fan shroud doesn't have any gaps on the sides. My restorer and I can’t figure out what next to try. We are thinking buy a new off the shelf water pump and see if that works, then a new radiator. Problem is I have an original radiator and spent $750 to have a new core put in.
Any ideas on what could be causing this would be very appreciated.
Thank you,
Rex
Le Mans Master
Joined: Jan 2007
Posts: 6,003
Likes: 1,509
From: Prescott Arizona
Rex - Since you already had your radiator recored, it might be okay. Before you just replace it out of hand, when it's running, check with an IR gun at both hose bibs and see what the difference is.
It might not be the problem so why possibly spend another grand if you don't have to.
Mike T - Prescott AZ
It might not be the problem so why possibly spend another grand if you don't have to.
Mike T - Prescott AZ
Thread Starter
Instructor
Joined: Feb 2023
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Rex - Since you already had your radiator recored, it might be okay. Before you just replace it out of hand, when it's running, check with an IR gun at both hose bibs and see what the difference is.
It might not be the problem so why possibly spend another grand if you don't have to.
Mike T - Prescott AZ
It might not be the problem so why possibly spend another grand if you don't have to.
Mike T - Prescott AZ
I agree and will use an IR Gun to check the temps of the hoses. I called the radiator shop that rebuilt it and he is honest and reputable. He told me before I buy another one to bring it back to him for a flow check. I am going to try a high dollar coolant that claims to lower the avg temps 10-25 degrees. Cheaper and easy test.
If I did buy a new radiator, it would be a DeWitts and the one that is built to look like an OE. It’s $1,299 so not cheap.
Thanks to the community for all the great inputs.
Cheers,
Rex
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Check if it holds pressure. For 1/2 hour. That will tell you if the block/water jackets/head gaskets are holding. I have had a bad head gasket display the exact symptom. Does it build pressure really quickly? Feel the upper hose. Run while the pressure guage is on the engine.
Thank you.
Team Owner
Joined: Feb 2003
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From: Sitting in his Nowhere land Hanover Pa
2024 C2 of the Year Finalist - Unmodified
2015 C2 of Year Finalist
Don't waist your money on a gimmick product. As JohnZ said cooling fixes come in boxes not jugs.
