Overheating 70 350hp

[Mark P.]

Okay, here we go....driving yesterday in 90 degree weather on the freeway and the temp creeps up to over 210 before pulling over. No loss of coolant. Infared scope confirms that gauge is accurate. After cool down, removed fail-safe thermostat that had stuck open...probably due to running at 210+. Replaced thermostat with 180 non-fail safe and replaced coolant, burped it and it idled at 180 degrees.

As soon as I hit the freeway, it immediately went to 210 and stayed there...this car never stays at 210, by the way. No leaks, no overflow after 20 miles on stop and go in the heat. FYI, fan clutch spins freely like it is not doing it's job, but that shouldn't make a difference at freeway speeds, right?

Car has had the radiator totally re-cored, but I don't know about the interior of the engine. It could be all gummed up in there. Doubt it though. Could it be a water pump impeller issue?

Thanks for the advice,
Mark

[Dennis D.]

Re: Overheating 70 350hp

Sounds like WP. Pull the belts give the fan a wiggle.

[John Walker]

Re: Overheating 70 350hp

Also, check and make sure the lower radiator hose cannot collapse. At freeway speeds there is a lot of "draw" on the intake side and if the hose can flatten out it would restrict the flow. John

[Doug Flaten]

Re: Overheating 70 350hp

In my opinion, 210 degrees is not overheating. You probably have 40 deg temp cushion before you truly overheat and exceed the boiling point of the coolant mixture. If you are not having any boil-over or loss of coolant, 210 is nothing to worry about in 90 deg weather.

[Pat M.]

Re: Overheating 70 350hp

I agree with Doug. In my opinion 210 degrees is not overheating. My 70 300hp frequently reads at or slightly above 210 degrees when idling for a while and/or in hot temperatures.

The PV manual seems to confirm this on page 38, where it states:

"During normal operation the [temp] gauge will read around 190 to 210 degrees F. Hard driving, heavy traffic with stop and go, or prolonged idling in hot weather will produce a gauge reading around 230-degrees F. If the gauge reaches 250-degrees F stop the engine and determine the cause of overheating ... ."

Patrick Moresi #45581

[Jim T.]

Re: Overheating 70 350hp

Patrick if your 70 is configured just like it came from the factory your vacuum advance does not get any engine vacuum when you are in heavy traffic with stop and go or prolonged idling in hot weather. My original owner 1970 350/300 had an early modification by me in 1970. One hot day in September I was out of my car and experiencing a rare moment of prolonged idling in hot weather. Had not had my new 1970 even two months yet. All of a sudden the engine idle really changed, rpm's increased. What happened was what the system was designed to do, at a specified temp the engine would deliver full time vacuum to the vacuum advance to help cool the engine. That discovery of how my new 70 operated made me change/modify the way it came from the factory. With a longer length of vacuum hose I connected one end to the vacuum advance and the other to the carbs vacuum port. No longer used the vacuum solenoid, just capped the vacuum connections. My engine ran cooler. Another benefit was increase of gas mileage in the lower two gears. My 70 is equipped with the tubo 400 automatic and full time vacuum advance normally was only when it shifted to 3rd. I was impressed with the ability of my 70 driving in downtown Dallas,TX traffic with the air conditioner on in July, and not having any heating issues with it. About 200-210 would be the most I would see in stop and go traffic and back down from that when away from stop and go traffic. With your 96 LT-4, if driving with the top down down the road and you encounter stop and go traffic and notice the temp go up, turn on the air conditioning. This will activate the coolant fans before the temp reaches the higher temp when they will come on anyway.

[Daniel S.]

Re: Overheating 70 350hp

I agree with others that 210 degrees is nothing to worry about on a 90 degree day.

[Pat M.]

Re: Overheating 70 350hp

Hi Jim. You're correct: In preparation for PV I have the TCS system on my 70 4-speed hooked up correctly, and thus at normal warm temperatures I get no vacuum advance at warm idle, and so the temp may climb near 230 with prolonged idling (it's HOT in Louisiana this time of year), as per the PV manual. And yes, before it reaches the boil-over temp of @ 250, the TCS engages, increasing idle and thus cooling.

Like you suggested, I normally by-pass the TCS and go with full vacuum advance all the time, which doesn't allow it to get that hot, but I'm now letting the engine function as designed in preparation for PV.

And you're also right that I usually keep my AC on in my '96 LT-4 regardless of the temp because it activates the cooling fans much sooner.

Regards, Patrick Moresi #45581

[Mark P.]

Re: Overheating 70 350hp

If it never ran this hot before, what would be the cause for the change, or should I just not worry about it? I should still replace the fan clutch, I imagine. I assume that only helps on city traffic at slower speeds, but that it should be operational.

Mark

[Stephen B.]

Re: Overheating 70 350hp

Last weekend, my 70 350/350 w/ 3.55 gears ran 230 degrees at 3,500 to 4,000 RPM's and did not lose any coolant in 95 to 100 degree weather. At idle, it only runs 140 degrees.