Mervruiser 3.7 oil pressure

[nailbender]

Hello.<br />I have a 1986 3.7 4cyl Mercruiser engine in my boat.<br />At a hot idle @800rpm it will have about 5psi oil pressure.<br />It only gets this low after a near full throttle run or pulling a skier around and the engine is good and warmed up.<br />As soon as I bring the rpms up the pressure goes over 20psi and will go up to 40psi at full throttle rpm.<br />I was told by my mercruiser dealer that this engine has large main bearings and doesn't run as much pressure as the other mercruiser engines.<br />Its been this way for 5 years with no problems.<br />I've had a mechanical guage in it to verify the pressure and have tried a different sender so I know the guage is reading accurately.<br />My Clymer manual calls for a minimum of 15psi at 2000rpm so I think I am in spec.<br />I've tried 30w, 20-50w and 20-40w oil and the pressures the same with all of them<br />Is my hot idle oil pressure normal for this motor?<br /><br />Thanks.

 

[waterone1@aol.com]

Re: Mervruiser 3.7 oil pressure

How many hours are on the engine ? I can't say that I have seen one that low.

 

[MrBill]

Re: Mervruiser 3.7 oil pressure

Nailbender:<br />I've had the same issue for several years with my 1988 3.7L. On initial start, when engines cold and oil is thick, the pressure is high. After running hard for a few hours and bringing to idle, pressure is very low...mine goes to 7-8. I starting using an additive 3 years ago to boost viscosity, combined with 20-50W oil and have seen some success (the 7-8 I mentioned, is up from 5-6 like yourself). In my case, I think much of the issue is simply wear, although from the beginning, it never ran 15-18 like you'd expect. My 1988 has never been rebuilt, has about 1400-1500 hours and runs so well I'll just keep pampering it until it shows signs of stress. I think you're seeing the same issues most original 3.7L's experience.

 

[nailbender]

Re: Mervruiser 3.7 oil pressure

Thanks for the help. I'm not sure how many hours are on mine.<br />I haven't had time to get the cover off and look.<br />I just changed oil a few weeks ago and put 30w in it instead of 20-50, but I did add a bottle of STP this time.

 

[moosejaw]

Re: Mervruiser 3.7 oil pressure

My 1986 has 350hrs on it and has been well taken care of and it has similar oil pressure. I thought an oil change (viscosity) was in order but after reading everything here it seems it will make little difference.<br />I have learned one thing...don't ask for opinions about what type of oil to use..it's an endless loop of very confusing info!!!!<br />Can't go wrong with Mercruiser 25w40 as far as I could tell.<br />I am more worried about if and how long this motor will hold up with proper maintenance.