How To Fix a Mazda RX-7
Advice on a 1983 Mazda RX-7 with a Fluctuating Oil Pressure Problem
Dec 4, 2007
This weekly Q&A session answers your questions about cars and trucks. This week explores a 1983 Mazda RX-7 with an oil pressure problem.
Question:
I have a 1983 Mazda RX-7 with 88,000 miles, 12A rotary engine, 5-speed manual transmission and 4-barrel carburetor, all stock. For the past month my oil pressure has been erratic. What I mean by erratic is, at times I won't have oil pressure for about a minute or so after starting. Oil pressure might drop about 15 minutes into driving for a minute or so and some days the oil pressure fluctuates by 30 lbs on an even drive.
There are also times when the oil pressure is fine. I found that if the oil pressure begins to drop to about 30 lbs. I can kick the 4-barrel carburetor in and the oil pressure will come back up. I changed the oil and oil filter and nothing has changed. Please help.
Thank you, Gary
Answer:
It is odd to have a 4-barrel carburetor on what is, essentially, a 2-cylinder engine. That rotary engine, technically called a Wankel Engine, was a very good engine although it is very fussy about normal maintenance.
The fact that the oil pressure comes and goes would tend to indicate the loss is not due to engine wear, but rather a mechanical fault which narrows things down a bit.
The first thing to do is to install a mechanical oil pressure gauge on the engine to determine if it is an oil gauge/sending unit problem or an actual oil pump problem. Chances are pretty good it is a faulty Oil Pressure Sending (OPS) unit. After you install the oil pressure gauge drive the car and if the oil pressure still acts up then you know for sure it is an oil pump problem.
Inside the oil pump is a pressure relief valve. Its purpose is to relieve excessive oil pressure due to a clogged oil filter. Often the internal spring breaks causing intermittent or total oil pressure loss. The pressure relief valve is not replaceable separately. The solution here is to replace complete the oil pump assembly.
Replacing the oil pump on this engine is not an easy job. If you are thinking about doing it yourself you should have a moderate to advanced skill level and allow about nine hours for the job.
That's all for this week. Feel free to browse the archives for past topics and other resources. And, as always, if you are stuck and need an immediate answer you can always call Vince on the phone. And if you are looking for Holiday gifts, read Holiday Gifts For The DIY.
