I am thinking about switching from Havoline synthetic to Mobil-1 oil due to price, but I have a couple of qts left of the Havoline.
Can I combine them when I change my oil, or should I just buy 3 more qts of Havoline for my final Havoline oil change?

I'm not a petroleum engineer, so I can't give you an educated answer on this one, but I personally would not do it. Petroleum based oils are all made from the same stuff, and are required to meet the same specs, so mixing them is safe. Synthetics all have to meet the same lubricating specs, but are made of different ingredients. It would be anybody's guess how these different ingredients might react to each other.

Your engine is worth a lot more than a few quarts of oil, so I'd drain it really well and put your new brand in without mixing brands.

You will be fine.

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70 SS 454 CI Dynoed 684 HP, 702 TQ All Aluminium Fuel Injected Small Block , plus 200 - 500 HP NX nitrous system.

I spoke with the Mobil 1 rep at a GM show for the service guys and he said if your using synthetic and need a quart while on the road and can't find any, you can add regular oil to top up.

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Mark D
1970 Z28
http://members.rogers.com/mlvd/

We've had a few crankcases full of Mobilzoil and Royal Redline that worked just fine.

thats like asking can i fill up my car at another gas station and be ok.......

<font face="Arial,Verdana" size="2">Originally posted by ddeennis:
thats like asking can i fill up my car at another gas station and be ok.......</font>

Just as long as you don't mix octane levels, lol (NOT)