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Merc 7.4L Oil Pressure

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seidh

New member
I have an issue with my oil pressure since I changed oil and filter a few weeks ago. I have 1994 29' Fountain sportfish cruiser with a single Merc 7.4L MPI (Engine year 2000) with Bravo 3.
The pressure has always been within 35-45 psi range (idle - plane speed). After the oil change after a couple hours using the boat I noticed the pressure dropped to 20 psi. I tested the gauge - good. I bought and installed new sending unit and the pressure came back to 35 when I started it, but dropped again to 20 after 1/2 hour running, and then even lower - to 15 psi at idle, coming back to 20-ish at higher RPM (2000).
Oil level is right on the money, no leaks, nice healthy yellow color. The engine runs fine, at normal running temp(160 - sea water cooled). I used same oil type, Castrol straight weight 30.
Oil filter I used is Mercruiser filter bought at the dealer (correct part#), and I noticed it gets really hot (you can't almost touch it) when the engine is wormed up.
My next step would be to change oil and filter again (or just the filter?) and see what happens.
I have an oil temperature gauge on my dashboard, I can see it is hooked up, but it doesn't work, does anybody know if there is a sending unit somewhere on the engine and how it works?
Thanks,
Seid
 
You are in San Diego where the temp is always warm. Using 30 wt. oil is not the best for 7.4L. You should use at minimum Merc. 25W40 or a synthetic like Mobil 1 15W50. I used both in a 4.3L and the oil was never hot even after a 5 mile hard run at near WOT. Make sure the oil cooler is getting sufficient waterflow. When was the last time you rebuilt the seawater pump? Verify it is working properly. Change the filter and use a heavier oil even if it is only a straight 40 wt.
 
So, I changed oil and filter again on Friday, used Mobil 1 15w-50 full synthetic and new bosch oil filter. The pressure came back up into the 45-50 psi range. Went fishing on Saturday, everything looked good. I'm pretty sure it was a bad oil filter that was causing that pressure drop.
Thank you guys.
 
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