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327 Boil-over problem

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Old 01-17-2018, 06:08 PM   #1
Surf454
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Default 327 Boil-over problem

Hi, gang, and thanks in advance for any help!

Have a well-worn '64 that was 'gifted' with a '62 327 engine by prior owner. I understand that may have no bearing on my issue, but just wanted to be complete in my posting.

A mechanic decided to replace my radiator cap with 'original' (Delco with a red snap lock) during a tune-up.

Thereafter, the car would spray coolant out of the overflow tube like a fire hose AFTER turning the engine off. The mechanic suggested we put an external fan on the radiator which we did. No change.

So much coolant was expelled, that it almost drained the radiator completely. The engine also ran at 220 degrees. I had already put two thermostats in the car, hoping that might be the problem.

A savvy NAPA guy suggested I go with a 10-lb. radiator cap instead of the 'original' one suggested.

Fortunately, the engine temp dropped and now hangs at 190, unless at a series of stop lights, then it goes up to 200.

Hoping I'd solved the problem, I turn off the car yesterday after a 10-minute jaunt, and the overflow hose dumps 3 litres of coolant.

Might I have a clogged radiator, or is it something I'm overlooking?

THANKS for any advice!
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Old 01-17-2018, 06:14 PM   #2
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I would find a new mechanic that would trouble shoot a problem instead of throw parts at it. if that was the original rad cap he replaced I hope you got it back.

first I would do some simple things. first run the car until the t-stat opens up without the rad cap on to make sure there is no air trapped in the system. after that let it cool down and check the level. fill if needed. next check the timing and the vacuum advance is working. check your fan clutch if you have one. also go over all the hoses and make sure they are all good
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Old 01-17-2018, 06:19 PM   #3
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Observe the "full cold fill" level on the over tank.
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Old 01-17-2018, 06:24 PM   #4
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I would find a new mechanic that would trouble shoot a problem instead of throw parts at it. if that was the original rad cap he replaced I hope you got it back.

first I would do some simple things. first run the car until the t-stat opens up without the rad cap on to make sure there is no air trapped in the system. after that let it cool down and check the level. fill if needed. next check the timing and the vacuum advance is working. check your fan clutch if you have one. also go over all the hoses and make sure they are all good
Unfortunately the 'mechanic' disposed of my original radiator cap. About how much time should elapse to open the thermostat (or is that just until it hits 190?) The mechanic did set the timing with thetune-up and the car seems to idle high. I'll follow your other instructions, thank you!
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Old 01-17-2018, 06:28 PM   #5
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Unfortunately the 'mechanic' disposed of my original radiator cap. About how much time should elapse to open the thermostat (or is that just until it hits 190?) The mechanic did set the timing with thetune-up and the car seems to idle high. I'll follow your other instructions, thank you!
I would hit the mechanic up for about 200 dollars for lost parts. I would not trust the gauge too much. get your self a IR gun to check your self.
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Old 01-17-2018, 07:33 PM   #6
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I would run a 16 pound cap that I tested on a pressure tester before installing. That, and make sure the overflow tank is at its proper level and not over-filled, as previously stated. It is normal for heat soak to raise engine and coolant temps after shut-down. You need a cap that can handle the extra pressure. No downside to running a decent 16psi cap.
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Old 01-17-2018, 07:40 PM   #7
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With the engine cold make sure the overflow tank is half full. Go get yourself a good quality 15lb radiator cap and try it again, your temps cooled because the 10lb cap is holding more pressure so the correct 15lb pressure cap should keep the coolant in the system.
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Old 01-17-2018, 08:51 PM   #8
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Unfortunately the 'mechanic' disposed of my original radiator cap. About how much time should elapse to open the thermostat (or is that just until it hits 190?) The mechanic did set the timing with thetune-up and the car seems to idle high. I'll follow your other instructions, thank you!
I've measured right at 5 minutes from a cold start.
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Old 01-17-2018, 08:58 PM   #9
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wait.
before the mechanic tuned and
changed the cap it was fine?

if it always ran too hot and overflowed,
i would put a 160 thermostat in it.
personally i think by time the 190 opens there is too much hot areas impeeding proper flow.
bet the car still runs 190 with a 160 thermo.
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Old 01-17-2018, 10:45 PM   #10
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Quote:
Originally Posted by Surf454 View Post
Unfortunately the 'mechanic' disposed of my original radiator cap. About how much time should elapse to open the thermostat (or is that just until it hits 190?) The mechanic did set the timing with thetune-up and the car seems to idle high. I'll follow your other instructions, thank you!
The next thing you need to read is below - it's the "bible" for understanding and diagnosing your Corvette cooling system; most "mechanics" don't have a clue.
Attached Images
File Type: pdf CoolingRestorer2013.pdf (627.5 KB, 86 views)
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Old 01-19-2018, 02:25 PM   #11
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With the engine cold make sure the overflow tank is half full. Go get yourself a good quality 15lb radiator cap and try it again, your temps cooled because the 10lb cap is holding more pressure so the correct 15lb pressure cap should keep the coolant in the system.
Closest cap size they had was 16lb. I tried a new one per your advice. wish it would have fixed the issue. Finally took it to hot rod shop, they say it's radiator crap build-up and suggested I have radiator rotted out. Thanks for your help!
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Old 01-19-2018, 02:28 PM   #12
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wait.
before the mechanic tuned and
changed the cap it was fine?

if it always ran too hot and overflowed,
i would put a 160 thermostat in it.
personally i think by time the 190 opens there is too much hot areas impeeding proper flow.
bet the car still runs 190 with a 160 thermo.
Hot rod shop said a lower thermostat might not fix the core problem. They think there's build-up in the radiator, so I guess I'm headed there next to have it rotted out. Appreciate your suggestion!
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Old 01-19-2018, 02:29 PM   #13
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Closest cap size they had was 16lb. I tried a new one per your advice. wish it would have fixed the issue. Finally took it to hot rod shop, they say it's radiator crap build-up and suggested I have radiator rotted out. Thanks for your help!


Don't you mean "rodded out?" I mean, if it's rotted out, it's of no use to anyone.

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Old 01-19-2018, 02:32 PM   #14
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I would run a 16 pound cap that I tested on a pressure tester before installing. That, and make sure the overflow tank is at its proper level and not over-filled, as previously stated. It is normal for heat soak to raise engine and coolant temps after shut-down. You need a cap that can handle the extra pressure. No downside to running a decent 16psi cap.
I tried a new 16lb cap per your advice. I hoped it would have fixed the issue. Finally took it to hot rod shop, they say it's radiator crap build-up and suggested I have radiator rotted out. Thanks for your help again GTOguy, I'm always happy to try the cheap way first!
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Old 01-19-2018, 02:33 PM   #15
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Don't you mean "rodded out?" I mean, if it's rotted out, it's of no use to anyone.

https://youtu.be/DoqIs49GMKQ
Thanks for setting me straight, can you tell I'm a noob?!
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Old 01-19-2018, 02:36 PM   #16
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I would find a new mechanic that would trouble shoot a problem instead of throw parts at it. if that was the original rad cap he replaced I hope you got it back.

first I would do some simple things. first run the car until the t-stat opens up without the rad cap on to make sure there is no air trapped in the system. after that let it cool down and check the level. fill if needed. next check the timing and the vacuum advance is working. check your fan clutch if you have one. also go over all the hoses and make sure they are all good
Did your t-stat open with cap off trick, had shop check timing and vacuum advance. They will replace hoses when they put in rodded out radiator. Thanks Nowhere man!
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Old 01-19-2018, 02:40 PM   #17
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Quote:
Originally Posted by Surf454 View Post

So much coolant was expelled, that it almost drained the radiator completely. The engine also ran at 220 degrees. I had already put two thermostats in the car, hoping that might be the problem.

A savvy NAPA guy suggested I go with a 10-lb. radiator cap instead of the 'original' one suggested.

Fortunately, the engine temp dropped and now hangs at 190, unless at a series of stop lights, then it goes up to 200.

Hoping I'd solved the problem, I turn off the car yesterday after a 10-minute jaunt, and the overflow hose dumps 3 litres of coolant.

Might I have a clogged radiator, or is it something I'm overlooking?
Quote:
Originally Posted by Surf454 View Post
Closest cap size they had was 16lb. I tried a new one per your advice.
.....and suggested I have radiator rotted out. Thanks for your help!
Quote:
Originally Posted by Surf454 View Post

..... I guess I'm headed there next to have it rotted out.
I think you're hiking your leg on the wrong tree.

Any of the radiator caps you've had on the car should have kept it from kicking coolant out the overflow, assuming the system was pressurizing and the temperatures you reported were correct.

You can't rod out (rotted out) an OEM aluminum radiator. You can rod out (rotted out) a copper replacement radiator. Even a copper replacement radiator should have worked in this situation if it was in good condition.

Plain water in the cooling system boils at 212* with no pressure cap at all so you should be able to leave the cap all the way off at the latest temperatures you report and not have a boil over. Have you verified your actual engine temperature with something other than the dash gauge?

You haven't indicated if this problem started before or after your mechanic tinkered with the car.

Without any further "facts", I'd suggest you look at a compression leak into the cooling system.

Lot's of information missing here.

Last edited by MikeM; 01-19-2018 at 02:43 PM.
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Old 01-19-2018, 02:57 PM   #18
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Hot rod shop said a lower thermostat might not fix the core problem. They think there's build-up in the radiator, so I guess I'm headed there next to have it rotted out. Appreciate your suggestion!
no problem. been chasing heat for years.
i found a defective fan clutch was an issue, slipped when hot.
then i chased thermostats.
found that, i guess from new gas blends, that by time the
190 opened, there were hot spots in the block that
wanted to stay hot.
a 160 solved that.

as far as rad rework, here again times have changed and
buying a new rad is more cost effective.
i use to go to rad shops for rodding and soldiering thinking
i was saving money.
guess labor and epa here in ca made buying a new one the better choice.
i like modine, and afr.

needless to say, car finally runs at the temp i want.
goodluck
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Old 01-19-2018, 03:08 PM   #19
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Originally Posted by MikeM View Post
I think you're hiking your leg on the wrong tree.

Any of the radiator caps you've had on the car should have kept it from kicking coolant out the overflow, assuming the system was pressurizing and the temperatures you reported were correct.

You can't rod out (rotted out) an OEM aluminum radiator. You can rod out (rotted out) a copper replacement radiator. Even a copper replacement radiator should have worked in this situation if it was in good condition.

Plain water in the cooling system boils at 212* with no pressure cap at all so you should be able to leave the cap all the way off at the latest temperatures you report and not have a boil over. Have you verified your actual engine temperature with something other than the dash gauge?

You haven't indicated if this problem started before or after your mechanic tinkered with the car.

Without any further "facts", I'd suggest you look at a compression leak into the cooling system.

Lot's of information missing here.
Thanks, Mike!

Honestly, I've never had the car running long enough to know if the problem occurred before the mechanic tinkered with the engine, so I can't be 100% sure.

Hot rod shop stuck what I think was a compression leak tester into the coolant fill tank today with blue liquid in it and said "good news, the color didn't change": I assume that indicates that I don't have a compression leak? Sorry for my lack of technical knowhow/lingo!

The shop gave me a copper radiator from another '64 that looks better than my copper radiator for rodding out.

There is an aftermarket Sunpro temp gauge in the car. Are you saying an IR one for $10-20 is a better actual indicator? If so, I'll get one and see if the problem still occurs when the cap is off and report details.

Appreciate your preventing me from prematurely hiking my leg on the wrong tree!
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Old 01-19-2018, 03:10 PM   #20
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Are you 100% sure that the engine ran uneventfully before the tune up/rad cap replacement, with no boilover on heat soak (shut-down)?

What, exactly was tampered with during the tune up?

Did the mechanic "adjust" the fill level in the surge tank from where it had been before?

If the answer to both of these questions show nothing of interest, then you either have a faulty cap, or you should replace it with a STANT 15# cap. You don't need a "Lev-R-Vent" type cap.

Last edited by 65tripleblack; 01-19-2018 at 03:14 PM.
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