Questions and Answers
Mazda Rear Main Seal
Q. Hi Vince, Is there any way to definitively tell if the rear main seal is leaking on this car? It is an 1989 Mazda 929, SOHC 18 valve with an automatic transmission. The car has about 110,000 miles on it. I bought it at 60,000 and the engine was dry and clean. I very stupidly put in synthetic oil in the hopes of keeping everything working deep into 200,000 miles.
The car immediately began leaking oil and I when next changed (3,000 later), I put regular oil back in hoping it'd stop leaking. Didn't work, still leaks. The dealer said rear main seal but I see oil at the top of the bell housing which makes me think it might just need all the upper end gaskets changed. BUT, if it is the rear main I want it fixed and it's a very expensive job.
Even though I'm pretty good with car repairs I'm pretty sure pulling the transmission in the driveway is more than I can handle. I want to somehow verify the dealer's diagnosis of rear main leak since they also said they would have to do the valve cover gaskets etc so even if it was dry afterwards I'd never really know how much of the $1,500.00 they're quoting me was really needed.
Thanks Much,
RichardA. The best way to tell is to pull the transmission and flywheel out and look at the seal. But we really don't want to do that at this point.
I would clean the top of the bell housing and the valve cover area with carburetor of brake cleaner. Then spray it down with Gunk engine cleaner following the directions on the can. Let it soak for a while and wash it all off and let it dry. Start the engine and take it for a ride around the block. Take a look at the suspect area and see if there is any fresh oil coming out.
If not, take it for another ride around the block and look again. Do this until you are convinced that it is indeed where the oil is coming from or not. If there is no oil coming from there, look at the bottom of the transmission where it mates to the block. There is a small notch there. If you see oil dripping out of that notch, then it's a damn good bet the rear main seal is leaking.
As for the cost, the seal is about $17.00 and about 4.5 hours labor. In my shop it would run from $300.00 to $350.00 to replace the rear main seal. Valve cover gaskets are about $14.00 each and the labor is about 2.5 hours. Again, in my shop it would run about $150.00 to $175.00.
Additional Information provided courtesy of ALLDATA