My mr2 keeps blowing rear main seals what causes this?

Asked by Feb 19, 2018 at 06:30 PM about the 1985 Toyota MR2

Question type: Maintenance & Repair

5 Answers


If not driven much its probably drying out,or there's a burr on the crank shaft.


Excessive crankcase pressure, which might be caused by a plugged PCV system. A proper rear main seal *should* be able to handle pressure, whether from oil pressure buildup or crankcase gases - it comes down to was it the right part and was it installed correctly, how many miles on the motor, wear on the crank, etc. Try thoroughly checking the PCV (positive crankcase ventilation) system.

No one can find a POV valve on this motor!


It depends on the motor you have - it will either have a PCV valve or just a vent hose, from valve cover back to intake, if it's fouled or plugged, pressure will build up in the crankcase. With engine running, slowly remove oil filler cap, does it feel like there was pressure escaping? (don't worry if engine stalls, a loose oil cap lets unmetered air into these engines and can stall them, just put cap back on and it will run normally again.) The whole point of all this is to determine if there is pressure building up in crankcase as a possible cause for seal leaking. It might just be a case of a bad replacement seal, especially if it was "cheated" in. (meaning the engine was left in place instead of being pulled and crank dropped).


It threads into the valve cover.

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