Jim Grant's Tech Tips
'91 VW Jetta, Cold Runner
the head gasket blew in my '91 VW Jetta , and I had to get it replaced.
Ever since then, it seems to run cold, which didn't appear to be a problem
in summer, but now in winter this seems to be amplified. I do a lot of
motorway driving, and after about 30 miles down the motorway, the engine
temperature will just fall away, and all of a sudden it loses power. (I
had the temp sensor checked and replaced, but it still made no difference).
If I drive around town, the temp seems to go up to 3/4 but never misbehaves.
If I stop the car when the problem occurs, and sit revving the engine
to get the heat back up to normal, it's fine again- like it never happened.
The car was serviced just before this happened, and I have changed the
oil, fuel and air filter (K&N air filter now installed) and the HT
leads (spark plug wires) have all done less than 15,000 miles. It's infuriating!
suggest a thermostat and making sure that the coolant is mixed 50% anti-freeze
to 50% water. The thermostat not only controls coolant temperature, it's
job is also to maintain the temperature to prevent fluctuation in the
coolant temperature. The fuel injection in your vehicle monitors coolant
temperature to determine the correct fuel delivery and to manage many
other operating aspects of the engine. If the coolant temperature remains
too low, over time the computer will make adjustments that create a cluster
of driveability problems. Stabilizing the coolant temperature may very
well correct your problem. As for the coolant? The engineers at VW designed
their vehicles to operate with specified anti-freeze to water ratio for
coolant. These folks know their stuff and you do not mess with the recipe.