Volvo Penta MD 7A high oil pressure?

waterrat2 · #1 10-07-2009

I'm still new to diesel motors. In May 2006, I bought a 1965 sailboat with a 1984 (or so) Volvo Penta MD 7A in it. I used the boat all that summer with the only motor problems having to do with the starter (the former owner paid to have it re-build), the ignition switch (I installed a new one) and air in the fuel line (a longer story).

Since I needed to work on other projects on my "new" forty-year-old boat, the motor wasn't started for about 31 months. During that time I did fill it with antifreeze. I also drained and cleaned the fuel tank and pulled it to repair a few small leaks in it. This spring I re-launched, replaced the return fuel line from motor to tank (because it looked real old), cleaned the fuel strainer on the fuel pump, changed the fuel filter and learned how to bleed the fuel line. The motor started without trouble. After warming it up I changed the motor oil and filter.

This summer I've used the motor mostly (short 10 to 20 minutes at a time) to get out of and back in the mooring box, with two longer motor trips; one of them about two hours. It starts and runs fine, but I have noticed that the oil pressure gauge reads higher than what the manual says it should. After starting it quickly goes around 44 to 50 psi at idle and goes over 60 psi at a fast idle (about half throttle, out of gear). Under load it doesn't get much higher but that's near the top of the meter's range anyway. (Three years ago, I didn't know what it was supposed to read and didn't pay much attention, since it didn't read low and the alarm didn't sound.) I don't know how to verify if the meter is accurate but did check the voltage on both sides of the sender and it seems to be fairly constant 12.5 V (approximately) on one side with the other side changing voltage at higher rpm. This seems to me to say that the meter reading is not being affected by higher alternator output at higher rpm.

So my question is, how high is too high and when should I be concerned enough to spend money on getting the meter reading verified, or is there some reasonable way I can do it myself.

timebandit · #2 10-07-2009

I might change the oil filter.

If that didn't solve the problem I would remove the oil sender and install a mechanical gauge at that point and see if I still had high oil pressure. That would check the gauge and sending unit.

harbin2 · #3 10-09-2009

Waterrat
I also have an md7a (in my 81 Islander 30). I thought you already changed the filter but, if not, I agree with time bandit on both of his suggestions.
I have had lots of air in fuel line problems. It turned out being the inlet to the fuel pump was missing a "crush" washer on the banjo fitting. It was sucking air. Sounds like you solved your problems but in case it ever crops up again, try tightening that fitting or any fitting between there and the tank.
Mine is also a long story.
I have no pressure gauge on mine - just an alarm - I hope it works.
harbin2

waterrat2 · #4 10-10-2009

Thank you for the replies. I did change the filter when I changed the oil, but that thought reminds me that the filter the dealer sold me is smaller than the old one. She assured me that it was the new approved part number listed by Volvo, but I think I'm going to check with another dealer on Monday. If it is wrong and too restrictive, it would be a plausible cause. It's time to buy a new one anyway.

I bought that last filter (along with a fuel filter) when I got to Berlin in September 2006, but didn't install it then, because I had intended to do it out of the water after warming it up while flushing the cooling system. That never worked out because I couldn't get it started, the last of the "air in the fuel line" incidents. I just emptied the cooling water and filed it with anti-freeze and put off changing the oil, not knowing it would be for two and a half years.

I've read the suggestion about a mechanical gauge on other threads. Just where do you get one of those and are they "one size fits all"? I've tried to search this site for one but haven't had any luck.

By the way, my air-in-the-fuel-line problem does seem to be solved. It had only been a problem when the motor wasn't used for a week or so. During all that time out of the water, someone suggested that I always close the diesel-cutoff valve after shutting down the motor. My tank is in the keel and he thought there might be enough suction from gravity trying to pull the fuel back in the tank to pull some air in somewhere. The owners' manual (which I had downloaded from the Volvo site by that time) said to do that anyway, so now I make a point of it. I also cut off about an inch of the fuel line where it was clamped to the tank because it was a little rough.

Omatako · #5 10-15-2009

Please please please let me have a problem of too high oil pressure - mine hovers just above the red on idle and not much higher at running speed. The buzzer never goes off but my eyes always wander to the guage when I'm motoring.

Your sender unit may be a lower resistance than is required (faulty). Most automotive parts suppliers will sell an affordable guage and pipe setup that will screw directly in where the sender unit comes out. I would do this if I were you. With an appropriate tee you can have both.