Engine Overheating at Idle

[Bob B.]

[Rich G.]

Re: Engine Overheating at Idle

I just went thru this with my 66 327/350. Everything made a little difference but the final thing was to get the correct vacuum can and a working fan clutch. I already got a DeWitts rad a few years ago. You must have a vac can that will pull full advance at whatever your idle vacuum is. In my case, vacuum was 15 inches and I needed a B26 can.

Also, get an IR thermometer to verify your gauge is correct. Be sure your new fan clutch is really working properly. My symptoms were exactly like yours. Now it idles around 200 max on a hot day and cools to 170-180 when driving. This is on my gauge which I think is at least ten degrees high based upon the IR thermometer. Also, your timing overall is important, but I'll let somebody with more experience than me comment.

Rich

[Duke W.]

Re: Engine Overheating at Idle

With a 15 psi cap and a 50/50 glycol/water mix the boilover temperature is 265F. So why are you throwing money at a non-problem?

I take it this LT-1 is installed in a C1???

Higher idle coolant temperatures are typical of ported vacuum advance. So what does it have? Ported or full time?

Also, does it have a proper spec VAC for the LT-1 cam?

Duke

[Patrick H.]

Re: Engine Overheating at Idle

Have you verified that your radiator cap is working? I've seen repro ones that do not, yet $5 ones from the auto store work fine.

And, as Duke says, if it hasn't boiled over then you have yet to have a problem.

Patrick

[Timothy B.]

Re: Engine Overheating at Idle

Bob,

Radiator cap holding pressure is very important so be sure it's in good working condition.
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Make sure the radiator is filled with fluid and only a small air space if no expansion tank. On C2's the expansion tank can be at the same height or lower than the radiator top so filling the expansion tank 1/2 full can actually leave air inside the top of the radiator that will not be pushed out thus reducing cooling capacity. I suspect that is the reason the 66-67 radiators/core support are leaned in more lowering the top of the radiator so be sure there is enough fluid in the system.

At 210* I am not sure there is a problem, what's the highest the temperature goes on a hot day at idle, are the pullies the correct diameter. Water wetter and different water pump IMO are not the solution.

Is the vacuum advance connected to a ported or full manifold source. Is the radiater sealed around the sides so the fan pulls air through the radiator.

[Stuart F.]

Re: Engine Overheating at Idle

I almost lost an engine due to a Mr. Gasket thermostat recently. It was new and I was caught in a line of traffic checking in at a car show. The engine heated up some as expected, but cooled down during the show. On the way home, however, it ran fine until I jumped on it for a stretch and it went to immediate super heat, pucking out all the coolant. The thermostat had stuck closed. The only thing that saved it was that the engine was an L-76 with by-pass which worked as designed until I wound it up and it overwhelmed the system. All the coolant pushed past the radiator cap relief and out the overflow, and spewed past the cap top seal/neck on the expansion tank. Apparently, the thermostat opened full then, when it closed, it stuck (welded) it self in the closed position. I tested it after in a pan of water on the stove and never would open.

It's another case of Chinese junk. I replaced it with a Robertshaw style unit from a major vendor and it is now working fine.

Just to be safe, I'd scrap that Mr. Gasket unit if I were you and get a good one. Of course you don't know where any other ones are made now a days either. India, perhaps?

Stu Fox

[Terry M.]

Re: Engine Overheating at Idle

FWIW The last thermostat I bought for the Gen II LT1 from the Chevrolet parts counter in the AC Delco box was made in India.

[Bob B.]

[Wayne W.]

Re: Engine Overheating at Idle

I am supprised someone hasnt mentioned the obvious. It dont have enough air flow at idle.

[Timothy B.]

Re: Engine Overheating at Idle

Bob,

You want the vacuum control to be pulled to the limit approx 2" vacuum less than the engine makes at idle speed. Sounds like the source at the carburetor base is full manifold vacuum, double check with vacuum gauge.

How is the engine timed? I was going to suggest radiator cap not holding pressure but you say it's been checked. At 220* the fluid is not going to boil if the cap is tested and holding 15lb. 220-230* will not damage the engine..

Could it be that the car is not boiling over and just pushing excess fuild out because the radiator is overfilled and it's seeking it's own level. Every time you refill the radiator and the fluid expands it pops the cap to push excess out and this does not mean it's boiling over.

[Bob B.]

[Duke W.]

Re: Engine Overheating at Idle

There's no such thing as a "16#" VAC. VACs are rated at start and max. advance at inches Hg vacuum.

What is the ID number stamped on the VAC mounting bracket? Have you tested the VAC for proper function?

The LT-1 cam should pull about 12" at 900. Your data doesn't jibe.
If your temp gage is reading 210 or a little over and you say your pressure cap is holding 15 psi, then boilover is not possible, At what temp gage reading does it actually start to boilover?

Either your temp gage is reading low or the pressure cap is not holding spec pressure. Boilover with a 50/50 mix of water/glycol is 265F. What coolant mix are you running? How do you know the cap is "fine". Have you tested it with a pressure cap tester?

What is your current fan setup? Give at much detail as you can - like whether it's the original '60 OE setup (describe) or something else.

Don't assume that your VAC supply port on the carb is full manifold vacuum. Test it to be sure.

You need to provide test results, not just answers such as "fine". How do we know what you did to make that determination and whether or not that determination is correct?

Duke

[Joe L.]

Re: Engine Overheating at Idle

Bob------


The most common cause of this problem is a failed or inefficient fan clutch. What sort of fan clutch are you using?

Second, it can be caused by ineffective sealing of the fan shroud. Original C1 shrouds do not seal very well, so you may need to add sealing so that all airflow created by the fan is directed into the radiator and not bypassing it.

[Timothy B.]

Re: Engine Overheating at Idle

Bob,

I assume the statement spark advance is 14* means the inital timing is set at 14*. If the vacuum advance is connected to full manifold vacuum you should see approx. 29* total IDLE timing with your timing light as this is 14 inital plus 15+- vacuum advance.

Vacuum advance is in addition to inital and centrifugal advance, at WOT the vacuum advance will retard and the engine will see only the sum of inital and centrifugal advance which should be approx 34-38*.

At cruise speeds when the vacuum is high the fuel mixture is much leaner and the engine needs this additional vacuum advance to light the mixture sooner because lean mixtures take longer to burn. Many times the timing under these conditions is 45-50*, (initial plus centrifugal plus vacuum advance).

You can't just advance the inital timing to 29* and leave it as this will affect total WOT advance. You can advance the timing to 29* as a test to see if that cools the idle temperature, I bet it will..but be sure to set it back and fix the vacuum advance to work properly.

PS.. Dead spots on lawn make the wife mad, if you want pasta for dinner better be careful here

[Scott O.]

Re: Engine Overheating at Idle

FWIW I bought a couple of Robert Shaw USA T-Stats on Amazon for about $10 each. I didn't want to chance an import
Scott