Overheating SB C2 w/AC when not moving

[Elliott P.]

Elliott Pflughaupt (64440)
Frequent UserJoe Lucia (12484)
Beyond Control Poster

Elliott------

A higher flow waterpump will not necessarily improve cooling. In fact. in most cases it will be a detriment. That's because the real key to cooling is the amount of heat transfer that the radiator can accomplish. A higher flow waterpump may result in the coolant moving too fast through the radiator and, thus, insufficient residence time in the radiator.

I don't like the stamped steel impellers, either. However, virtually all modern cars use this type of impeller in the waterpump. GM began using this type of impeller in original and SERVICE small block waterpumps dating back to the mid to late 70's.

Richard Mozzetta (13499)
Super Moderator

Elliot,

I feel Joe has described it well.

Maybe what you're experiencing should be reviewed in a new topic, particularly with details of year, engine, hp and carburetor/distributor details. We could help you try to solve your issue.

It's possible that a ignition timing anomaly is going on and if ported vacuum, your heat buildup at idle/traffic could be corrected with a conversion to full-time manifold vacuum and a replacement VAC unit. There have been many discussions here revolving around Duke Williams' methods to do this conversion, all with excellent results to correct problems just like yours. When you raise your idle, a ported VAC will then become operational, adding timing which cools the engine.

I did this conversion on a 67 L71 (427/435) about 10 years ago resulting in a amazing difference. Since then many others.

Rich

Elliott Pflughaupt (64440)
Frequent UserRichard Mozzetta (13499)
Super Moderator

[Richard M.]

Re: Overheating SB C2 w/AC when not moving

Elliot,

I'd verify the vacuum source with a vacuum gauge at idle and note idle RPM.

I'd also check timing at idle to verify your VAC is operational. I don't know the 236 spec offhand. If you have a Mity-Vac you could use that to check that it holds vacuum. It's possibly defective.

Pull the hose off the VAC and plug it and verify static timining to spec.(look it up in the AMA Spec Data) available at gmheritage.com site.

Another thought. You Fan Clutch may be a suspect and needs to be verified too.

Rich

[Duke W.]

Re: Overheating SB C2 w/AC when not moving

Define overheating! The normal operating temperature range for a C2 is 180 to 230, and with a 15 psi pressure cap a 50/50 blend of ethylene glycol and water has a boiling point fo 265F.

Give us some temperature gage readings and the corresponding operating conditions and ambient temperature.

Hot running at idle can be caused by a dead fan clutch and/or VAC or a radiator clogged with deposits that reduces heat transfer.

Hot running at steady speeds up to freeway speeds is most likely a radiator issue as above.

Ethanol laced gasoline does not burn hotter than straight gasoline. Peak combustion temperature and EGT are primarily a function of spark advance. If optimized, peak combustion temperature is about 4500F and EGT is low. Reducing spark advance below optimum for a given operating condition reduces peak combustion temperature, which reduces engine out NOx and EGT increases, which keeps the catalyst hot to maximize both oxidation of HC and CO and reduction of NOx. So the spark advance map is a big issue in emission control.

On vintage non-exhaust emission controlled engines we are free to optimize the spark advance map (most OE maps are very conservative) and the only limiting factor is detonation.

Duke

[Mark E.]

Re: Overheating SB C2 w/AC when not moving

Top things I'd check with these symptoms:
- Ignition timing
- Seals between radiator and core support, and between hood and core support
- Radiator. It's amazing how much better a new core or complete radiator cools.

[Elliott P.]

Re: Overheating SB C2 w/AC when not moving

Thanks Rich, Duke and Mark for your consideration.

Rich, car not running right now due to me playing with some tidy-work on engine. I will try and get every thing back together in a day or so. Will do vac gauge at carb at idle. Will check vac adv function. Will verify static timing. However, all this was checked before with tune-up and carb overhaul while having problem. The fan-clutch and thermostat were also replaced with brand new parts.

BTW, is there a good shade-tree test for proper fan-clutch operation to avoid just replacing them?

DukeMark, as I said previously, the tune had been checked earlier, including timing. But, worth checking again. I will check out the seals you mention, but this car was judged a Top Flight Chapter car in Northern California Chapter, and I doubt they would have missed that. The car was fully restored about 12 years ago with minimal milage on the car since then. I do not know what was done to/about the radiator at that time; however, it seems to perform well in other driving conditions. Is there a good shade-tree test for checking radiator condition, short of just replacing it?

Thanks, and best regards to you all, Elliott

[Richard M.]

Re: Overheating SB C2 w/AC when not moving

Elliot,

As mentioned, when you take temperature measurements, also use a IR Gun at the black hose connection at the thermostat housing. This will confirm actual readings. Ideally they'll be close.

Since you said you get coolant spillage out the overflow, it certainly appears temp is very high.

Fan Clutch:
Please precisely define "New". Brand and Specs. Remember that the temp spec is "air" temp, not coolant temp.

I will tell you this. I had one unusual experience with a new reproduction I was never able to figure out. I had a '66 350hp L79 a few years ago. I did a body off to replace its badly rusted frame.

I discovered the original fan clutch was missing its thermal flat spring and valve plug. The car never overheated previously. I decided to replace it as it was of unknown condition.

I installed a new repro. It was the K&B unit, a proven functional unit that is a great product with nearly identical configuration, just missing date code placement as original(on the hub perimeter).

The engine temperature would rise at highway speed with this unit We swapped back to original. No rise. Back to new....rise again.

I tested the new unit and it passed. I forget the details but I worked with the manufacturer and saw the air specs were not exact to original. I couldn't get it in my head that this difference caused the problem. The manufacturer thought the radiator was at fault.

I never could get a handle why the new unit caused this problem. I put the original back on. Been fine ever since, even with its missing spring and valve plug. A mystery.

Rich

[Duke W.]

Re: Overheating SB C2 w/AC when not moving

"BTW, is there a good shade-tree test for proper fan-clutch operation to avoid just replacing them?"

...a couple of ways. First, rotate the fan with the engine cold. Then do it again after shutdown when the temp is at least halfway between the mid point and the top of the scale. It should be a lot stiffer.

With the engine not fully warmed open the hood and rev the engine to about 3000 and note the sound and feel of the air flow. Do it again as above when very hot. The noise and airflow should be noticeably greater.

Most replacement fan clutches are "tuned" to a 195F thermostat, so they won't tighten until the temp is well over 180. That's one good reason to have an OE clutch rebuilt.

Duke

[Gary B.]

[Mark E.]

Re: Overheating SB C2 w/AC when not moving

Is there a good shade-tree test for checking radiator condition, short of just replacing it?

On some radiators (I don't know about the design of yours) you can glimpse the end of some tubes by peering into the radiator cap opening with a good light. Do you see scale, muck, rust or build up? Or is it nice and clean?

Visually look at the outside of the core and look for repairs. Has a tube been pinched or soldered shut? Dirt or debris in the fins? Damaged or bent fins? Scan the core with a laser temperature gun to look for hot or cold spots that may indicate a blockage or repair.

My experience is after 40k - 60k miles, even a well maintained radiator (most aren't) will cool the engine noticeably better after the core is boiled out or replaced. Degraded radiator performance first shows up when they are stressed- idling or low speeds in hot weather; continuous high speed operation; towing; going up a long grade.

[Elliott P.]

Re: Overheating SB C2 w/AC when not moving

Thank you all for all the input. I have done some homework on previous input, and I must now confess that this old engineer may well have been overthinking the problem. As stated, I believed the engine tune had all been sorted out by previous work and multiple exams. However, as suggested by Rich, I did check the Vac-Adv with my handy Mity-Vac and it is as dead as a doornail. (Yeh, Mity-Vac checks good.) That is my first order of business, replacing Vac-Adv (I didn’t even need to get engine details back together to get it running). The Vac-Adv is a ‘236’ (with 16 degree advance indicated in stamping) which I believe is correct unit. Ordering part tomorrow. This certainly feels like a eureka moment. I will be following up on all the other inputs while waiting for part.

BTW, the old fan-clutch that was replaced with a new one (no change in problem), they both are coded ‘CK’ which is supposed to be for a Big Block, with a 0.3” shorter shaft. I was told that they had replaced the fan-clutch with one for a BB, and did not think anything about it (assuming it might afford better cooling?). Now I see that the pully alignment might be off by 0.3”, which I must assume should be fixed. Hey, what else do I have to do in my life?

BTW2, I am a retired 80 year old (former engineer) who self-identifies as a “crap-mudgeon”. Yeh, I don’t like putting up with crap. But, that’s life, and the alternative is worse.

Thanks again for all your inputs, and I still have some work to do here.

Best regards, Elliott

OOOPPS! Overthinking again. Shorter shaft on fan clutch will not affect pully alignment. What is effect of fan being 0.3" further away from radiator and further out of fan shroud? This old engineer would not think much of an effect, but would appreciate more expert opinion.

[Richard M.]

Re: Overheating SB C2 w/AC when not moving

Elliot, Great work, you did it. At idle you were simply running only at static timing, probably around 8 or 10 degrees Adv. Add that 16 or so and your engine will be cooler.

I'd also summize that your idle speed was lower than normal and had to be raised when the VAC went south.

Word of caution though. You said you ordered a new 236. Word on the street is all repro "numbered" VACs are all the identical operational spec, only stamped differently. iirc Duke has the scoop on that somewhere. I seem to recall they're a B1 "Boat Anchor"(or Mooring may be more appropriate...lol), renumbered to satisfy judging only. What a hoot.

Whatever the vac Start-At and All-In spec is for the 236 should be noted, and you may want to get a off the shelf properly spec'd VAC instead. I.E. maybe a B26 or B20.

I'm on a dUmbphone in my camper and my specs are on my laptop which only runs wifi(none here) and the Velcro encased carry case would certainly wake up the wife and doggie so can't get in there right now.

And your Fan Clutch..... Yes, the BB unit you have there will work, but as noted it's spaced in the shroud incorrectly. Hub to pulley is identical. I'd fix that VAC before anything and get after the Fan Clutch later. Best to do one change at a time.

The effect of a .3" delta will be a bit less cooling but I'd think hardly noticeable.

Rich

[Duke W.]

Re: Overheating SB C2 w/AC when not moving

Unless I missed something all you said was SB with AC. What's the year and engine configuration?

Duke

[Duke W.]

Re: Overheating SB C2 w/AC when not moving

On some radiators (I don't know about the design of yours) you can glimpse the end of some tubes by peering into the radiator cap opening with a good light. Do you see scale, muck, rust or build up? Or is it nice and clean?

Visually look at the outside of the core and look for repairs. Has a tube been pinched or soldered shut? Dirt or debris in the fins? Damaged or bent fins? Scan the core with a laser temperature gun to look for hot or cold spots that may indicate a blockage or repair.

My experience is after 40k - 60k miles, even a well maintained radiator (most aren't) will cool the engine noticeably better after the core is boiled out or replaced. Degraded radiator performance first shows up when they are stressed- idling or low speeds in hot weather; continuous high speed operation; towing; going up a long grade.

All the above is good for conventional copper/brass radiators with integral tanks and fill cap, but C2 small blocks have a furnace brazed aluminum radiator with no side tanks or cap. These systems have a remote expansion tank with the fill cap. The are not repairable by conventional radiator shops.

The Dewitts exact reproduction is an excellent replacement. Copper replacements can cause hot running because for the size of the core they do not transfer heat as efficiently.

Use of a modern HOAT antifreeze like Zerex G-05 and changing it every five years (including pulling the block drains to drain it all) should give decades of service life.

It's also VERY IMPORTANT to verify that the mounting grommets (two bottom one top) are in good shape and the radiator is electrically isolated from the chassis. If not you've got an iron-aluminum galvanic cell and aluminum is the sacrificial material.

Duke

[Richard M.]

Re: Overheating SB C2 w/AC when not moving

Unless I missed something all you said was SB with AC. What's the year and engine configuration?

Duke

Post #1 bottom..... 1965 L79 non TI stock config.

[Mark E.]

Re: Overheating SB C2 w/AC when not moving

All the above is good for conventional copper/brass radiators with integral tanks and fill cap, but C2 small blocks have a furnace brazed aluminum radiator with no side tanks or cap. These systems have a remote expansion tank with the fill cap. The are not repairable by conventional radiator shops.

The Dewitts exact reproduction is an excellent replacement. Copper replacements can cause hot running because for the size of the core they do not transfer heat as efficiently.

Use of a modern HOAT antifreeze like Zerex G-05 and changing it every five years (including pulling the block drains to drain it all) should give decades of service life.

It's also VERY IMPORTANT to verify that the mounting grommets (two bottom one top) are in good shape and the radiator is electrically isolated from the chassis. If not you've got an iron-aluminum galvanic cell and aluminum is the sacrificial material.

Duke

Good point. My 1970 doesn't have a radiator cap opening either, so a visual inspection of the tubes isn't possible. But whether it involves replacing a core or replacing the entire radiator, the difference in cooling capacity can be significant.