Return From Vettefest - Fingers Crossed

[Stuart F.]

Just returned from our local October Vettefest in Old Town (Florida). The registration line took so long that I saw about 195 degrees on my L-76 63 with all the idling. I have a new 180 thermostat in it and it has been performing fine. On the ride home on SR417 it ran well holding good oil pressure and right at 180 temp. Then my son and I had to manuver some to get to our exit (he has a 96 GS). I passed him and ran up to about 100 mph in order to get past some other cars, so when I made the exit and started to brake and down shift, between gears my son said I was blowing out a lot of blue/black smoke. When I got to the stop light, the temp was pegged at 245 and it was pucking out antifreeze out of the overflow bigtime - so much that my wheels spun trying to start out again. I nursed it home (about 2 miles), and it continued to puck coolant.

Preliminary check of things showed;
- no broken or split hoses,
- nothing out the side of the block,
- oil looks at right level with no sign of coolant
- coolant tank is all pucked out/empty.

Engine started up as if still hot, i.e. had to crank and give it more gas, but it seemed to run ok with normal idle speed and no unusual noises, so I moved it into the garage.

My thoughts/hopes are that perhaps the thermostat stuck open and it just plain overheated, specially under the stress of high rpm's.

Any thoughts?

Stu Fox

[Rich P.]

Re: Return From Vettefest - Fingers Crossed

Stu,

one reason it could have been hard to restart is thet the gass in the bowls boiled off with the heat soak from sitting. I'd also check the overflow cap to see if it holds pressure.

Rich

[Gerard Q.]

Re: Return From Vettefest - Fingers Crossed

First I would check the lower radiator hose (squeeze with your hand). Under high rpm it can collapse because the internal coiled wire is no longer up to the task. If thats ok check that the rad cap can hold 15 psi. I assume the thermostat is ok since you replaced it however new ones can fail. The good ones fail in the open position to prevent overheating.

[Terry M.]

Re: Return From Vettefest - Fingers Crossed

My thoughts/hopes are that perhaps the thermostat stuck open and it just plain overheated, specially under the stress of high rpm's.

Any thoughts?

Stu Fox

I think you meant to say that you hope the new T-stat stuck closed. Sticking open will not, by itself, produce overheating.

[Stuart F.]

Re: Return From Vettefest - Fingers Crossed

All good thoughts fellows. Thanks.

My cap is old but pretty. Believe it is a 13#, not 15#.

My thought on the thermostat sticking open is an old theory that came to mind first; that of how back in the day guys would race without a thermostat and their engines would overheat due to the coolant at high RPM didn't stay in the radiator long enough to get cool. Now that I think about it, this was just a short high speed blast and should not be the case with mine. I have never had a coolant system problem with this car except I lost a radiator in 1975 due to a chemical reaction (change between brands of antifreeze) ate pin holes in it.

As many times as my carb has boiled out fuel or lost it by evaporation you'd think I would know the symptoms, but I guess I was just too shook up and expecting the worst.

Thanks again guys. Really appreciate your help. Believe I will sleep better tonight. I'd really hate to lose a numbers matching engine that way. I got to sit down and do the math to figure what my tach saw on my downshift back to third at about 110 mph (it will wind up there though with the 3.36 and CR).

Stu Fox

[Terry M.]

Re: Return From Vettefest - Fingers Crossed

My thought on the thermostat sticking open is an old theory that came to mind first; that of how back in the day guys would race without a thermostat and their engines would overheat due to the coolant at high RPM didn't stay in the radiator long enough to get cool. Now that I think about it, this was just a short high speed blast and should not be the case with mine. I have never had a coolant system problem with this car except I lost a radiator in 1975 due to a chemical reaction (change between brands of antifreeze) ate pin holes in it.

Old theory all right -- as in old wives tale. This a deep subject best left to the fluid mechanics guys, but my understanding is that it just don't work that way. If it went too fast through the radiator it would also be going too fast through the engine and it wouldn't puke out of the system.

As it cools down check some things -- like the spring in the lower rad hose, the t-stat operation -- you might consider the old pan of boiling water test. Last, but not least flush thoroughly radiator and engine.

[Clem Z.]

Re: Return From Vettefest - Fingers Crossed

Old theory all right -- as in old wives tale. This a deep subject best left to the fluid mechanics guys, but my understanding is that it just don't work that way. If it went too fast through the radiator it would also be going too fast through the engine and it wouldn't puke out of the system.

As it cools down check some things -- like the spring in the lower rad hose, the t-stat operation -- you might consider the old pan of boiling water test. Last, but not least flush thoroughly radiator and engine.

robertshaw thermos fail in the open position.

[Stuart F.]

Re: Return From Vettefest - Fingers Crossed

As it turns out the thermostat is a Robertshaw that I installed this past spring. At that time, I did a thorough engine flush including the block which spit out a lot of crud. My hoses all look quite good, i.e. no collapse in the bottom hose, no splits or signs of leaking, etc. They were not that old, but as my son reminds me, everything deteriorates a lot faster here in Florida - specially rubber products.

If there is any obvious thing I overlooked, it would be the cap. It is a correct 13 lb unit which, as I mentioned before, still looks pretty, but I have no record of when I last replaced it. When the overheat occurred yesterday, coolant was primarily coming out of the expansion tank overflow as well as around the top of the cap seal to the neck. So, I don't know, is this a sign of a failed cap or one that's operating properly??

My attack plan is; 1) to remove the thermostat and test it's operation in a pan of water, and replace it if suspect. 2) replace the cap, 3) charge it with water and run it through a warm up cycle. If it tests out ok, then re-charge it with 50/50 coolant and then, 4) follow Duke's advice to limit my runs (up and down) to 5500 RPM.

Thanks for all the good suggestions and advice. You've all been very helpful. And, yes, I did sleep well last night.

Stu Fox

[Russ S.]

Re: Return From Vettefest - Fingers Crossed

Stu, You can have your cap pressure checked to make sure it is up to specs. A lower than suppose to be pressure will cause the coolant to boil at a lower temp than a higher pressure cap. Russ

[Timothy B.]

Re: Return From Vettefest - Fingers Crossed

Stu,

If this is the 307-13lb. cap it's very possible the rubber seal is not holding pressure. This will lower the boiling point, do you recall if the system went under pressure as can be felt at the top radiator hose...

I would check the radiator cap first, there should not be any leakage between the cap and tank.. you may find the problem there.

[Stuart F.]

Re: Return From Vettefest - Fingers Crossed

Russ & Tim;

The cap is a correct AC 307 13#, but the history of age or source are unknown as yet. I may have bought it along with the dated expansion tank from De Witt's back in the 80's or 90's. My original tank was replaced along with the radiator in 1975. The tank I replaced it with at that time was a 1975 dated one with welded connections, but I went back to one with correct 63 date and rolled connections. My point is that I have been treating that tank with kid gloves to avoid breaking one of the connections loose as they are fragile. As such, I've been leaving the cap well enough alone as long as the system was working well. The thought occurred to me of going to a 15# cap for driving here in Florida, but I did not due to my concern for that tank.

I don't recall making a special effort to check the top hose for pressure before, but it looked normal. I certainly will include that in my routine in the future. Good thought.

I see the prices on the correct replacement caps range from a low of $30. (Zip) up to $46. (Dr. Rebuild). The rest are all at $35. or $39., It's hard to know who is handling the best product. Guess I'll have to test them first to be certain they hold at or near 13#. I don't have the means to do it, but I imagine I can find an Auto Parts store that can.

Thanks guys for your thoughts. As always, this forum is a good one stop research source.

Stu Fox

[Dan H.]

Re: Return From Vettefest - Fingers Crossed

Hey Stu, there's an 307 cap on Ebay, good shot of it, shows the subtle differences from the repros. 'AC' slightly tilted, arrows closer to the center depression etc. If a repro is like that one, it's pretty good!
Dan

[Joel T.]

Re: Return From Vettefest - Fingers Crossed

Stew;

A couple of other thoughts for what they are worth....

Lower radiator hose... can collapse and stop flow.. how old is that spring in there?

Exhaust restriction... less likely given you were doing 100! Aside from heat, the car just won't take the gas....

Heat riser valve free? (that's why I use a spacer!)

Just as a precaution, you might do a compression test and watch the leak down rates, cylinder to cylinder.

How is the car running after you filled the coolant back up.. Any smoke at idle? How are the plugs?

Good luck,

Joel

[Domenic T.]

Re: Return From Vettefest - Fingers Crossed

Stu,
I think the lower hose sucking closed at high RPM is a good posibility, Also try to spin the water pump pulley by hand and see if it spins in the belt. That can happen at high RPM's causing the pump pulley to slip and over heat.

DOM

[Stuart F.]

Re: Return From Vettefest - Fingers Crossed

Dan; Thanks. I'll check it out.

Joel; I have not re-charged the cooling system as yet to test it further, but after it cooled down Saturday, when I started it to move it into the garage, it cranked a while which I guess I should expect. But, once it started, it seemed to run well with no apparent noises or smoke, etc. I didn't leave it run too long, just enough to make those observations.

The lower hose (spring) felt firm from the engine to the radaitor (no apparent weak spots). The hoses were replaced in July 1996 (less than 6k miles ago). Other than calendar age, they look like new. When I flushed the system this past spring, I had the top hose off and it looked very clean inside. The only crud I got was from the block drains, and that I expected from the lower cooling passages in the block. Every engine I've done this way blew out a lot of crud from there.

My heat riser butterfly operates very freely. However, I too am intending to replace it with a spacer soon (I'm waiting for some cooler weather to do my projects). I ground out the spacer round (no valve flats) so I'm looking forward to see how it works.

I agree that I really need to check out the engine closely with a leak down test. It was on my project list anyway. In the back of my mind, I fear a worse case scenario with perhaps ring damage or even a blown head gasket. My son, who was behind me, said he saw a lot of blue/black smoke each time I downshifted, along with the white coolant steam just before I stopped. I tend to goose it for an RPM match before I let out the clutch when I'm in a hurry to whoa, so maybe that's some of what he saw. He's a certified A & P as well as a commercial pilot, but that don't mean he knows cars all that well.

Thanks to you both for your responses. I'm going to have the cap tested this afternoon, and may be able to fill it with water and do some more checks.

Stu Fox