1989 740 blow by

nisan17 · Post by **nisan17** » 03 Apr 2012, 18:59

HI Group,

In the last couple of months I used the OBD to diagnose that my Throttle Position Switch is defective. Since I don't drive said car but a couple times a week for a few miles, I haven't replaced same. Now, the other dilemma that arose very fast is that two weeks ago, I noticed oil coming from the oil filler cap making the valve cover wet and the exhaust manifold smoke. The oil level was good. Now, just today I had to jump the battery to drive it and upon opening the hood there was oil every where, on the fan, belts/pulleys and the block on the side of the filter was all wet. Of course it appears to have come from the cap and it doesn't show on the stick.

I've read somewhere maybe it's a defective cap. I've also read that the PCV system is plugged. My oil was half way through before a change.

Any ideas as what to check and how?

Thanks in advance,

nisan17 · Post by **nisan17** » 05 Apr 2012, 21:08

http://www.ipdusa.com/products/5890/110 ... arator-box

i think i found the problem

Post by **billofdurham** » 06 Apr 2012, 12:23

Kevin,

How long is it since you changed the sealing ring on the oil filler cap? When they get old they do let a lot of oil out onto the top of the engine.

If the flame trap is blocked that makes the problem worse. It is rare for the oil separator box to cause this problem but the flame trap, part #5 on the attached, is a common problem.

740 PCV Diagram.pdf: (478.77 KiB) Downloaded 424 times

Bill.

nisan17 · Post by **nisan17** » 06 Apr 2012, 15:24

Thanks again Bill. Gonna get the gloves on anyway and clean and inspect the system. As well as maybe a new filler cap. The sealing ring, hmm, never knew that! Can I get that part anywhere or should I just get a new cap, they're not that expensive?

Post by **billofdurham** » 10 Apr 2012, 12:07

IPD does an after-market seal for the grand price of $0.33. A cap with seal is $17.13.

I have only replaced a cap once when one of my trainees forgot to put it back on after he topped up the oil.

Replace the seal as the caps don't usually wear out.

Bill.

nisan17 · Post by **nisan17** » 10 Apr 2012, 13:02

Thanks Bill

nisan17 · Post by **nisan17** » 20 Apr 2012, 16:32

Bill, I've replaced my flame arrester(plugged), oil filler cap seal and replaced my throttle switch, along with an oil change. I just drove it a short while and now see that oil is coming from under the timing belt cover. I will pull the belts and all off tomorrow. Could the crankcase pressure have caused a seal or two tio blow? Also, which one is likely to blow?

Thanks much in advance,

Post by **billofdurham** » 21 Apr 2012, 12:20

Pressure in the crankcase can cause oil leaks. On the front end of the engine check the camshaft, intermediate and crankshaft seals.

Bill.