C3 running warm on highway

[Dale P.]

Here it is the night before we leave to go to BG and our LS5 is acting a little lazy ... here is the scoop ... good clean raditor, good water pump, nice mixture of antifreeze to water (50/50 mixture) all good hoses, good fan clutch, new termostat ( can not remember if it is 160 or 180)... all the seals around the rad are there and in good condition .. BUT here is the surprise .. at highway speeds 60 MPH the temp rises to about 210f (and that is when the temp was around 80F outside) ... if I then take a "back" road and run at 40 MPH the temp drops down to around 180/190 F .. The only thing that I know for sure is that the timing is just a little advanced so to 10/11 degrees Vs the books suggestion of 8 .......I have thought about pulling the thermostat for the trip .. but I really shouldn't have to do that ... A friend of mine (who races) suggested retrading the timing to about 6 degrees ... he also feels that I am pulling additional air into the intake manifold because the gasket under my gas cap is gone (it is a "sealed" cap) .. this too will make it run lean .. thus hotter

what are you thoughts and suggestions ...

[Mike McKown]

Re: C3 running warm on highway

My thought is your friend probably doesn't win many races.

For starters, if the thing doesn't puke antifreeze out when you shut it off after elevated speeds on the highway with say a 12-14 pound pressure cap, I wouldn't worry about it.

I'm sure you will get all kinds of advice on what to do but if you want to make BG at this late date, drive on if the paragraph above applies.

[Patrick H.]

Re: C3 running warm on highway

To follow Mike's line of thought, I swapped a generic but new cap from the auto parts store onto my 72 for the drive to Seven Springs. Cheap insurance.

Patrick

[Wayne P.]

Re: C3 running warm on highway

All good stuff,but if this doesn't do it, your radiator is partially plugged. Hot at low speeds is air flow, hot at high speeds is water flow. This rule of thumb has never failed me.

[Duke W.]

Re: C3 running warm on highway

Retarding the timing will likely make it run hotter. You say you have a "good clean radiator", but what does that mean? When was the last time the tanks were removed for a thorough core inspection and rod out of the tubes? Just testing the radiator for "flow" means nothing.

With a 15 psi cap and a 50/50 glycol/water mix, the boiling point is 265, so at 210 you still have 55 degrees margin. Check to make sure the vacuum advance is correct and functioning along with the TCS if so equipped, and you may want to overhaul the radiator later this year if everything else checks out.

Duke

[Dale P.]

Re: C3 running warm on highway .. All good stuff

Duke,

The rad was completely gone through flow checked and pressure tested this past winter by a local professional rad shop .. The cap is new and also has been pressure tested at 15 PSI .. The cooling system too has been pressure tested and is fine .. I have verified the gage reading against a mechanical thermometer and it reads very close through out the scale .. The reason I am concerned is that I have never seen this car raise its temp before on the road .. so I am thinking there is a problem brewing .. the vac advance works as verified by watching the marks with a timing light ... The TCS system works ( at least you can heard the solenoid energising etc) but I do know that the dist. vac advance is connected directed to the carb and not through the TCS carb solenoid ... It has always been that way and I guess I figured if that works don't mess with it ...

[Duke W.]

Re: C3 running warm on highway .. All good stuff

"The rad was completely gone through flow checked and pressure tested this past winter by a local professional rad shop..."

I not trying to be argumentative or pedantic, but this means nothing. As I said previously, "flow testing" tells you nothing about the radiator's ability to function as a heat exchanger. If "completely gone through" means they removed the side tanks and rodded out the core tubes, then the radiator is probably okay. If the tubes were not inspected and rodded out as necessary, the radiator is suspect. If they just did a pressure check and "flow test" the tubes could be full of deposits that are acting as insulation, which is preventing the radiator from transfering heat from the coolant to the air.

You might want to look at your RO and/or talk to them and find out exactly what they did. A complete overhaul including a rodout would probably be in the range of $100 to $200.

Duke

[Michael W.]

All C3 Corvettes depend on a chin spoiler

under the nose of the car to divert adequate air to the radiator whilst in motion. Even a base engine car will suffer if this piece is missing. Seems to me that some year big blocks had a flexible secondary spoiler extension also.

[Gary S.]

Re: C3 running warm on highway .. All good stuff

As has been stated, flow testing tells you nothing. My 66 ran hot on the highway like your 72. It had the original radiator, etc, etc. The problem is the sediment and the precipitates that come out of solution normally. You probably have a partially plugged radiator and your engine is producing too much heat for your radiator to dissipate. A partially plugged radiator will flow well, will leak check well, will pressure test well but will run hot at highway speeds.

Gary
72 LT1

[Tom R.]

Rule of Thumb: C3 running warm on highway

I'll have to remember that...like a footnote in archives!

"Hot at low speeds is air flow, hot at high speeds is water flow. This rule of thumb has never failed me."

[Michael W.]

This rule of thumb

is true when referring to engine speed, and in most cases also to car velocity, but not on C3s. They depend on airflow at high speed also. See my post below.

[Harmon C.]

Re: All C3 Corvettes depend on a chin spoiler

Mike The extension was used on 73-74-454's with A/C.

[John H.]

Re: C3 running warm on highway .. All good stuff

Cooling basics - if the coolant carries heat to the radiator faster than the radiator can transfer it to the air, you have problems. 99% of highway-speed cooling problems relate either to a radiator that can't cut it any more due to the insulating properties of internal scale and corrosion (especially "original" radiators that "look good"), lack of adequate airflow through the radiator due to obstructions in the airflow path or a missing lower air dam, or a lower radiator hose whose internal spring reinforcement has corroded away, allowing the lower hose to collapse at higher rpm. One of these is likely to be your problem.

[Dave Suesz]

On the other hand, the C1...

cooled very well. When we were living out in the country, we had so little "city" traffic my Dad removed the fan to save on gas, and never had a heating problem. Don't try this today, unless maybe you live in Wyoming or something. In SE PA, the number of traffic lights in our area has more than doubled in the last ten years.

[Dale P.]

Re: Is it possible that ...

Here is a more up to date information and more clarification ...... the rad. now has a brand new core section .. both top and bottom hoses are new, new by pass hose, new heater hoses, new overflow tank cap, new water pump .. new fan clutch, all of the rad pieces, seals, etc are 100% there and intact .. new 160F thermostat .. verfication of correct temp sending unit data ( I even tested it to be sure it reads correctly by using boiling water .. and it read 210F) ... so this leaves only two potential areas ... the new water pump is not an NOS and I beleive it is rated at a higher water volume flow then the stock unit ... the only other thought is the heat being generated by the automatic trans .. that the rad must also disapate .. SO the question is can the transmission be generating that much heat ( for whatever reason) that it will affect the cooling water temp on the engine itself ? OH by the way the car still runs exactly the same .. at 40 MPH temp is fine at 60 MPH .. runs 210-220F .. no matter what the air temp is outside