My daughters '98 Subaru overheats in below freezing weather if you drive it above 50 mph. If you drive for an hour at lower speed and gradually speed up it seems ok, but if you just let it warm up to normal temp at idle and get right on the highway it overheats. In above freezing weather it runs great, temp is very stable, never loses any coolant. One dealer and one independant mechanic couldn’t find anything wrong and insisted it couldn’t be the thermostat (which I asked them to change). She finally got it to a dealer in the overheated state and they say it has a cracked block. She said “How sure are you?” and they said “Very sure”. It’s not worth an engine rebuild so, taking Tom and Ray’s usual advice, I went to the parts store and looked for products with the word “miracle” on the label and bought some block sealer. But here are my questions. How can a cracked block make the car overheat without losing coolant? (it doesn’t, unless it gets really hot and I don’t see water in the oil) For block sealer to work, won’t the block have to be leaking at the time? Thanks, and sorry this is so long!
This really doesn’t sound like a cracked engine block to me. I think it would overheat in any weather if this were the case.
However, if it truly is a cracked block, I had very good luck with K & W seal. This was a very long time ago–back in the winter of 1961-62. I had a cracked block on my 1947 Pontiac. The block had cracked around a couple of the valves (this was a flathead engine and the valves were in the block). I put the cylnder head back on and filled the radiator with water and K & W seal. I ran the engine as directed, drained the radiator and block, put in fresh coolant and oil and was back in business. I sold the car 6 momths later and two years after that it was still being driven.
To answer your question, I guess you can use this K & W treatment anytime. However, I think that either a block leaks or it doesn’t. In my case, I was definitely getting coolant in the oil. If you aren’t getting the coolant in the oil and there isn’t an external coolant leak in the block, I would look somewhere else for the overheating problem.