Engine Overheating at Idle

[William C.]

Re: Engine Overheating at Idle

Vacuum advance has several nice properties, not the least of which is matching the advance to the engine load. An engine idiling under no load will be much happier (run cooler and be more steady) with an advance that is well above what the engine would tolerate under load at the same rpm. Likewise under light loads at speed, the engine is more efficient with vacuum advance in use because of the lean mixtures under cruising speed light load conditions. Start by getting a vacuum advance can that matches the SHP engine specs from GM, The best is part number 1116236 as used on all the 365-375 hp corvette smallblocks and other application with low idle vacuum. You should make sure the vacuum advance is getting full time vacuum from your carb, not ported vacuum which is essentially inop at idle. Once that is under control you should be in good shape. The GM part number above can be converted by your parts supplier to the equivalent unit at your local parts store.

[Stuart F.]

Re: Engine Overheating at Idle

Regardless of what is stamped on the VAC, check and verify it's performance to spec with a MityVac. Take it to the store with you, if need be. I have seen so many VAC's of late mis-stamped or plain failing to meet specs. Many of our aftermarket vendors buy their parts from the same few sources, as do the major retail/wholesale auto parts stores. It took me a long while and many sad experiences to finally find a good one - believe it was from GM Partsdirect, and I think we cleaned them out some time ago.

Stu Fox

[Michael F.]

Re: Engine Overheating at Idle

First I would make sure I have the right clutch for my stock fan. Good chance you don't. I would also use an electronic thermometer to get an accurate reading.

I recommend behind radiator, under stock shroud. The SPAL fan from DeWItts is best as a pull not a push fan.

BTW 210 degrees (if it holds steady) is not unusual in summer heat and will not hurt your motor. Going over 220-240 is a problem.

[James S.]

Re: Engine Overheating at Idle

A big THANK YOU to the contributors of this thread and others on "engine overheating at idle".

After replacing the radiator (which had sprung a leak) and the water pump, I bought a NAPA, B22 VAC ('67 300 HP) only to find out that someone along the way had stuffed the VAC hose with a tip off a glue tube - the engine had never had any vacuum advance. Needless to say the new VAC was not needed.

What a difference in the temperature and the performance boost is significant. The temperature has not risen higher than 180 degrees where as before the temperature was getting up to 220-230 degrees at idle.

Much Appreciation to those that share their expertise on the TDB - It's great to be able to drive without keeping an eye on the temperature gage.