Oil changes on an old car

I have a 1988 Mazda that leaks oil a bit. It goes through 3 or 4 quarts every 5,000 miles(the changing interval they suggested for synthetic oil).
The junk in it should be caught in the filter and a lot of the oil is being changed out during those 5,000 miles. My question is would this let me change my oil less frequently without any harm?

I’d switch to regular oil unless sythetic’s required, and keep changing it every 5k. Old engines have lots of blow by to contaminate the oil.

I don’t know if the Mazda cars had the same engines as the trucks. Open the hood and look for the sticker that tells you what weight oil is recommended. If it says 30wt and not 5W30wt or 10W30wt, you want thicker oil. Straight 30wt is much thicker than multiweight oil.

You will still save oil by using the straight 30. After all, it’s an 88 car so you can experiment. Of course, if you live where the temperature stays in the low 20s F, the engine may not start with the thicker oil.

Synthetic oil is a waste of money on this car. You are not changing out oil just because you add a lot. I don’t think there has been a car sold here since the Korean war that called for straight 30 weight with the possible exception of air cooled ones.

@oldtimer I agree that synthetic oil is a waste oif money in this case. I would buy a regular mineral oil in the weight recommended (likey 5W30) and just keep topping up and change at 5000 or the interval recommended.

OP still has to change the filter, and a longer interval is not recommended, since, as you say, blowby will dirty the oil.

With motor oil going for $4/qt, I’d start looking at fixing the leaks…Gently tighten the oil-pan and valve cover bolts and see if that helps…