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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