We've been caught in an early suzero blast here in Iowa and I have Rotella 15w40 in the crankcase of my 1990 NA 740 wagon 250,000 miles. Any real harm to be done until I can change oil on a warmer day? The oil light doesn't seem to stay on any longer than usual (1 or 2 seconds) and in this kind of cold I let this elderly car warm up 3 or 4 minutes after a dead cold start.

Hey Claude,


As was mentioned earlier, I don't think its going to cause harm, but I think it would be much easier on the starter and battery if you used a 5W-30 grade oil. The yellow bottle Pennzoil or the other major brands would do just fine.


Seasons greetings, Jon 'Uncle Olaf'

No harm, but watch out on warm up: be gentle. You should not be running 15-40 in that car: poorer startup lubrication, lousy fuel economy. Far better is a 5W-30 synthetic or even just any 5W-30 regular dino oil.
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See the 700/900 FAQ at the select shortcut button on the top right of the screen.

Mobile One full synthethic is not more expensive, especially considering you can go longer between changes. I've found the synthetic to be much easier to start in our cold climate than the dino.

--George Butler

Let it warm up some. That oil is to heavy for the cold. It will start blowing seals.