My guess would be the gutted thermostat. Water may be sailing through the system
too fast to absorb the heat properly. When it sits it soaks up the heat and acts
up. Learned this from an old mechanic who was a bit crazy but he was a great
mechanic.
Bruce Lowry
KGROWLER@aol.com wrote:
> My '79 1500 Midget has had problems lately with sudden overheating and
> burping coolant into the overflow tank.
>
> Background - About 98000 miles on the car. Radiator was recored 2 years ago.
> Water pump and fan clutch replaced last year. Running with a gutted
> thermostat in place. It runs on the hot side in hot weather and I have at
> times had to use the heater system for auxilary cooling when driving at
> Interstate speeds. It runs hotter at higher running speeds, will usually drop
> back down at lower speeds.
>
> The problem - I have had 3 sudden overheating situations in the last two
> months. The first time it happened was on the way home from Twist's after the
> car was shut off for a few minutes at a gas stop. We had gone about 150 miles
> with no problem, then after the brief shutdown to gas up, it immediately
> climbed into the red as I reentered the Interstate. The other odd
> circumstance was that the heater fan was on when the temp started to climb,
> but the air from the heater outlet was blowing cool air, not the very hot
> air I would expect from an overheating engine. I pulled off as soon as I
> could. The only sign of heating was a small amount of oil bubbling under one
> side of the valve cover and there was about 1 pint of antifreeze blown into
> the overflow tank. After about 45 minutes, the temp gauge was down
> considerably and we wnt the rest of the way home on surface streets with no
> problem. The second time it happened I had not stopped or shut down the car,
> it just started climbing while we were about 30 miles into a 40 mile trip on
> a 50 degree evening. Since then I have refilled the system with the front
> raised thinking it was an airlock but still had it happen again last weekend.
> I was heading for RoadAmerica when it did it for the 3rd time. It was only
> 50 degrees out, the car was running fine when I stopped to reclip a couple
> Tenax fasteners on the top. I shut down the car for 30 seconds to jump out
> and fasten the top. When I restarted and took off again, the temp gauge
> immediately climbed to the red. Letting it sit for 1/2 hour got the temp down
> to 1/3 of the way up the scale and I turned around and drove back home with
> no further problems.
>
> Any ideas? The cool air from the heater outlet when it happens throws me. I
> am about to pull the engine for a 100K rebuild but the spare engine is still
> not ready. I'd like to drive the car to the NAMGBR AGM in St.Paul in two
> weeks but not if I don't figure out what is going on here.
>
> Kim Tonry
> Downers Grove, Illinois, USA
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