Engine Overheat Problem

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helomec@gmail.com - 01 Aug 2006 04:29 GMT

Have a 68 Buick with a 430 V-8. The "Hot" light comes on when the car
has been driven and then sits with then engine off for approximately 20
min. If the car is started and the light comes on, I can rev the
engine up a bit and the light will go out. If I drive it below 75mph
the temp light stays out...if I drive it fast...then slow down and
drive 65mph...the light eventually comes on.
The engine was rebuilt about 2 yrs ago, the engine has a new radiator,
water pump, themostat and temp sensor. I took a chance and replaced
the water pump....no such luck. The sensor was checked to make sure it
works...works fine. I am thinking about replacing the radiator and
finding a differant fan. Any thoughts? Please contact me at
helomec@gmail.com.

Thanks!

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Scott Buchanan - 01 Aug 2006 06:34 GMT

Before dumping any more money into it, I would measure the temperature going
into and coming out of the radiator. This will tell you if it is doing its
job or if it might be a sensor problem. Some engines will get hotter when
shut off because of residual heat that is not taken away by circulating
water.

How stock is the engine, fan, and radiator? Is it missing a fan shroud? Are
the pulleys the correct diameter? Could be timing or carburetor adjustment.
The obvious is the thermostat. Has it always done this or is it a new
problem? Was coolant used when parts were new? water only would cause
corrosion.

> Have a 68 Buick with a 430 V-8. The "Hot" light comes on when the car
> has been driven and then sits with then engine off for approximately 20
[quoted text clipped - 10 lines]
>
> Thanks!

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Scott Dorsey - 01 Aug 2006 15:07 GMT

>Have a 68 Buick with a 430 V-8. The "Hot" light comes on when the car
>has been driven and then sits with then engine off for approximately 20
[quoted text clipped - 8 lines]
>finding a differant fan. Any thoughts? Please contact me at
>helomec@gmail.com.

If you measure the surface temperature of the radiator, what do you get?

Is the fan actually turning properly? If high engine RPMs makes the
light go out, it sure seems like you don't have proper airflow.
--scott

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"C'est un Nagra. C'est suisse, et tres, tres precis."

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jim - 01 Aug 2006 15:41 GMT

> Is the fan actually turning properly? If high engine RPMs makes the
> light go out, it sure seems like you don't have proper airflow.

I may be wrong but I think he is saying that high speed driving is what
causes the light to come on. He said "If I drive it below 75 mph the
temp light stays out...". Of course he said other things that seem to
contradict this also so we have to guess what he is really meaning.

But, if high speed is truly the only thing that leads to the light
coming on, I would guess the gauge is accurate (at least relatively
speaking). It clearly is getting hotter when driving 75 mph than it
normally does which it shouldn't. The sending unit might be a little bit
extra sensitive but there isn't anything about high speed driving that
would cause the gauge to behave differently other than temperature.
There are a couple things that immediately come to mind that might
cause this. Lower radiator hose collapsing (partially blocking flow) and
bad distributor advance. If the mechanical or vacuum advance in the
distributor are not working the engine produces a lot of extra heat at
high speeds.

-jim

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