Overheating Strategies (General)

[Christopher R.]

Last Saturday, I was stuck in a 4 mile backup to cross the Sagamore Bridge to Cape Cod. About 80F; stop and go; mostly stop. Classic overheat scenario. Temperature gauge starts to creep past the 180 where it happily sits most times, and there's still about 20 minutes of traffic to go until it clears. The temperature gauge is accurate - checked with an IR gauge.

What to do? Turned the heater on full. That helped some. But the needle is still creeping to the right.

In situations like this, is it better to let the engine idle around 750 rpms? Or, use the throttle to put the engine at a fast idle, say 1500 rpms? I know it's not helpful to continually shut off and restart the engine.

Not so much looking for why the car overheats, but what strategy to employ when stuck in traffic.

[Robert C.]

Re: Overheating Strategies (General)

Put the car in Neutral, rev up to 1500 RPM. If the temp doesn't go above 210 d.s you should be OK.

[Robert C.]

Re: Overheating Strategies (General)

Put the car in Neutral, rev up to 1500 RPM. If the temp doesn't go above 210 d.s you should be OK.

[Dale C.]

Re: Overheating Strategies (General)

What I do with my big block is to bring the rpm's up to 2000 to 2200 range and keep it there. Turning on the heater on highest temp and fan speed will always help also (it adds another small radiator to get rid of the heat). For me popping the hood doesn't seem to help. Good luck. Dale

[Dale C.]

Re: Overheating Strategies (General)

What I do with my big block is to bring the rpm's up to 2000 to 2200 range and keep it there. Turning on the heater on highest temp and fan speed will always help also (it adds another small radiator to get rid of the heat). For me popping the hood doesn't seem to help. Good luck. Dale

[Duke W.]

Re: Overheating Strategies (General)

If you were in a brand new Corvette the temperature will reach about 227F before the fans engage at high speed to bring it down to about 210. Then the cycle repeats.

Both a C2 (with a 15 psi cap) and a C5 will boil over at about 265F with a 50/50 water/glycol mix of coolant. Increasing temperature in low speed traffic is normal, and I wouldn't be overly concerned until it gets close to 230.

In the meantime, running the engine at 1500-2000 will increase fan speed without increasing the load that much, so the engine should cool down.

Also make sure the critical cooling system components - radiator, fan, and distributor vacuum advance are of proper specification and functioning properly.

Duke

[Duke W.]

Re: Overheating Strategies (General)

If you were in a brand new Corvette the temperature will reach about 227F before the fans engage at high speed to bring it down to about 210. Then the cycle repeats.

Both a C2 (with a 15 psi cap) and a C5 will boil over at about 265F with a 50/50 water/glycol mix of coolant. Increasing temperature in low speed traffic is normal, and I wouldn't be overly concerned until it gets close to 230.

In the meantime, running the engine at 1500-2000 will increase fan speed without increasing the load that much, so the engine should cool down.

Also make sure the critical cooling system components - radiator, fan, and distributor vacuum advance are of proper specification and functioning properly.

Duke

[Jack H.]

Agree with Duke!

Seeing 210-220F on the gauge isn't the end of the world. As Duke points out later cars with lower compression engines tended to 'naturally' have higher steady state temp profiles which is why we see temp gauges extend the upper end of the 'dial' as time progressed.

Yes, reving the engine and increasing air flow through the radiator + speeding coolant circulation through the block IS the right way to handle stop/go traffic stress on a hot summer day! Case in point: when emissions friendly designs began (early 70's), a thermal switch was added to the RH cylinder head. This switch had three positions: (1) engine below normal (switch closed), (2) engine in normal temp range (switch open), and (3) engine above normal (switch closed).

When engine temp was EITHER below or above normal operating range, the temp switch closed and acted to speed engine idle RPM. On some Corvettes, the increase in idle RPM was achieved by simply porting vac to the distributor. In other cases it was a combination of both vac to advance the distributor as well as a physical solenoid on the carb to 'bump' normal curb idle. The second case is how the system worked in '71 (vac advance + solenoid controlled idle RPM).

This is an abnormal operating condition that we don't 'test' during Performance Verification. But, I had the 'opportunity' to check it out in my '71 a few years ago. Note, the net increase in engine idle RPM for a typical '71 with the CEC system engaged is only 75-100 RPM higher than normal curb idle--not as much as you'd guess the car would need/want.

Well, our NCRS chapter attended a local town's 4th of July parade. Directly ahead of us was a local Corvette show 'n shine group with their vintage Corvettes. I overheard them talking before the parade started. The advice was to watch your temp gauge because it a hot day and we'd be a couple of hours in stop 'n go traffic. They told their club 'newbies' to turn the engine OFF then back ON should the temp gauge begin to creep toward overheat!!!!

I interjected that shutting the engine down was a bass-ack-wards 'fix' that would probably compound the problem and they should consider reving the engine. I was viewed as one of those smart-@%% NCRS dudes....

During the parade, I saw my temp gauge begin to climb. I did nothing. When it reached about 230F (SCAREY), the CEC 'clicked' in, the distributor got vac advance, the solenoid bumped engine RPM slightly and the temp gauge STOPPED climbing, slowly it began to fall and dropped back to roughly 210F. The CEC 'clicked' again and engine RPM fell to normal. The temp guage began to slowly climb again and I watched the cycle repeat 3-4 times. I made it through the parade A-OK....

The guys in the 'other' club had three of their cars genuinely overheat, pop the rad cap, and deliver geysers of underhood steam. Each had to be hand pushed off the parade route where the owners waited for the engines to cool with serious looks on their faces. One of their cars let go DIRECTLY in front of the parade's reviewing authorities. It was their club's 'kingpin' who'd told the others how to sucessfully cope with stop/go heating stress by shutting the engine off!!!!

[Jack H.]

Agree with Duke!

Seeing 210-220F on the gauge isn't the end of the world. As Duke points out later cars with lower compression engines tended to 'naturally' have higher steady state temp profiles which is why we see temp gauges extend the upper end of the 'dial' as time progressed.

Yes, reving the engine and increasing air flow through the radiator + speeding coolant circulation through the block IS the right way to handle stop/go traffic stress on a hot summer day! Case in point: when emissions friendly designs began (early 70's), a thermal switch was added to the RH cylinder head. This switch had three positions: (1) engine below normal (switch closed), (2) engine in normal temp range (switch open), and (3) engine above normal (switch closed).

When engine temp was EITHER below or above normal operating range, the temp switch closed and acted to speed engine idle RPM. On some Corvettes, the increase in idle RPM was achieved by simply porting vac to the distributor. In other cases it was a combination of both vac to advance the distributor as well as a physical solenoid on the carb to 'bump' normal curb idle. The second case is how the system worked in '71 (vac advance + solenoid controlled idle RPM).

This is an abnormal operating condition that we don't 'test' during Performance Verification. But, I had the 'opportunity' to check it out in my '71 a few years ago. Note, the net increase in engine idle RPM for a typical '71 with the CEC system engaged is only 75-100 RPM higher than normal curb idle--not as much as you'd guess the car would need/want.

Well, our NCRS chapter attended a local town's 4th of July parade. Directly ahead of us was a local Corvette show 'n shine group with their vintage Corvettes. I overheard them talking before the parade started. The advice was to watch your temp gauge because it a hot day and we'd be a couple of hours in stop 'n go traffic. They told their club 'newbies' to turn the engine OFF then back ON should the temp gauge begin to creep toward overheat!!!!

I interjected that shutting the engine down was a bass-ack-wards 'fix' that would probably compound the problem and they should consider reving the engine. I was viewed as one of those smart-@%% NCRS dudes....

During the parade, I saw my temp gauge begin to climb. I did nothing. When it reached about 230F (SCAREY), the CEC 'clicked' in, the distributor got vac advance, the solenoid bumped engine RPM slightly and the temp gauge STOPPED climbing, slowly it began to fall and dropped back to roughly 210F. The CEC 'clicked' again and engine RPM fell to normal. The temp guage began to slowly climb again and I watched the cycle repeat 3-4 times. I made it through the parade A-OK....

The guys in the 'other' club had three of their cars genuinely overheat, pop the rad cap, and deliver geysers of underhood steam. Each had to be hand pushed off the parade route where the owners waited for the engines to cool with serious looks on their faces. One of their cars let go DIRECTLY in front of the parade's reviewing authorities. It was their club's 'kingpin' who'd told the others how to sucessfully cope with stop/go heating stress by shutting the engine off!!!!

[Donald T.]

Re: Agree with Duke!

Did you ask him if he needed a ride?

[Donald T.]

Re: Agree with Duke!

Did you ask him if he needed a ride?

[Warren F.]

Re: Overheating Strategies (General)

Jack:

Great story!

Thanks for the explanation on how the solenoid system works on our '71's. I don't believe I've ever had the chance to hear it work on mine. When temp climbs to 220 or so, if stuck in traffic, I just take the sidewalk route or any other means to get out of Dodge, quick!

[Warren F.]

Re: Overheating Strategies (General)

Jack:

Great story!

Thanks for the explanation on how the solenoid system works on our '71's. I don't believe I've ever had the chance to hear it work on mine. When temp climbs to 220 or so, if stuck in traffic, I just take the sidewalk route or any other means to get out of Dodge, quick!

[Duke W.]

Re: Agree with Duke!

Yes, excellent expanation of the '71 emission control system.

What's noteworthy is that when the temp reaches a certain point, full manifold vacuum is delivered to the vacuum can to increase advanmce, and the reason was to help cool the engine.

For those who still think "vacuum advance isn't important" or "makes no difference", this should be illuminating.

Duke

[Duke W.]

Re: Agree with Duke!

Yes, excellent expanation of the '71 emission control system.

What's noteworthy is that when the temp reaches a certain point, full manifold vacuum is delivered to the vacuum can to increase advanmce, and the reason was to help cool the engine.

For those who still think "vacuum advance isn't important" or "makes no difference", this should be illuminating.

Duke