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Jim Grant Tech Tips Jim Grant Tech Tips
A collection of helpful articles based on reader submissions
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Below is a collection of Jim Grant's Tech Tips sorted by Vehicle Make. These Tech Tips were answers to questions submitted to Jim by users over the course of many years.
If you have any questions, please feel free to email us.



Lincoln - Mercury
  Jim Grant's Tech Tips

'91 VW Jetta, Cold Runner

Q: Recently 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!

A: I would 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.

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