Have I finally found out why my '69 MGB seems to run hot? Since early spring,
I have had a number of problems with the cooling system, which has severly
effecting the reliability (what you say? I expected reliability?) Although I
have had no overheating problems for the last six years, this year it overheats
at the slightest provocation, particularly heavy traffic on a hot summer day.
I have driven it so as to avoid boiling over - carry extra coolant, avoid
traffic, stop if it gets to hot. But I'm tired of watching the gauge! The
problems and repairs were as follows:
1) Early in the year, I did a lot of gauge watching, so I replaced and
calibrated the thermo sending unit. Using a digital thermometer, I calibrated
the dash gauge. Mine has no temperature values, just C, N and H. When the
gauge is exactly pointing down (middle of the N), the temperature of the
coolant entering the radiator is 180 F. About two-thirds of the way across the
dial is 200 F. If it reaches the white bar of the H, it is above boiling or
greater than 212. When I'm moving on the road, mine runs at about 200 F. If I
get stuck in traffic, it heads for the hot zone and I shut it off and wait.
Now I know how the gauge works and that the car really does run hot.
2) OK, this is the easy one. Change the thermostat, drive without one, drive
with the summer model (160 F). I've tried them all - still runs too hot.
3) While exiting an expressway (to avoid a traffic jam) the radiator developed
an incredible leak - the engine lost coolant, boiled over and generally
overheated. I had the radiator repaired, put in a new water pump, hoses, etc.
At this point, the cooling system holds coolant for the first time in years!
And, according to my calibrated gauge it still runs hot!
4) I run a compression check every fall and last year it was fine. Last night
I checked it out and it looks like trouble: 180, 105, 160, 165. Adding oil to
the bad cylinder gave no change in the values.
Will one low cylinder cause it to run hot? Whats the net wisdom concerning the
best approach to fixing this? Am I crazy to keep driving it? Should I replace
all the valves in the head? or is it just a blown head gasket?
Avoiding Traffic
Bruce Hamper
bchamp@ccmail.monsanto.com
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