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Jim Grant's Tech Tips
'98 Chevy S-10, Overheating Transmission
Q:
I have
a '98 Chevy S-10 pickup and the engine light comes on when the transmission
heats up. I have replaced the transmission fluid, filter, gaskets twice
and it lasts only about a day before the light comes on again. The truck
only has 47k miles on it and runs perfectly otherwise. It also won't shift
into overdrive when it heats up, stays in 3rd gear. Any suggestions?"
A:
The
first and most important question that has to be answered, is the transmission
really overheating? If so, what is causing the overheat problem? Heat
is the biggest enemy to an automatic transmission. The overheated transmission
oil transforms from a lubricant and fiction modifier to an acid with built
in sand paper. Burnt transmission oil just tears the inside of a transmission
apart. Because your transmission is computerized there is a possibility
that it is not overheating. It could be the Transmission Fluid Temperature
(TFT) sensor or wiring for TFT sensor that has a problem. The computer
for the transmission has what you could call a fail-safe strategy to minimize
damage to the transmission in the event the transmission is overheating.
The strategy is what you're experiencing when each shift becomes more
pronounced and the transmission is prevented, by the computer, from using
all the gears. This strategy is in an effort by the computer to minimize
shifting to reduce transmission temperature. You must have this problem
diagnosed and determine as mentioned before if it is a faulty sensor and/or
wiring or if the transmission is, in fact, overheating. If the transmission
is overheating then the transmission cooler should be inspected. Check
lines from the transmission to the cooler, be sure they are not bent/kinked
which would restrict fluid flow to the cooler. The cooler should be checked
for blockage and for flow rate. In any event do not delay, overheating
your transmission is going to put your check book in the red.
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