Shmitee

38' Fountain with twin stock HP500's. At cruising speed it seems 3500 to 3800 rpms everthing seems ok, but anything higher and it sets off the alarm and temp climbs over 260 degrees. Water temp stays at about 160 degrees. I replaced the thermostats and impellers. Water flow looks good.

Thanks!

blue thunder

I've been battling high oil temps as well. Lost number 3 main bearing in sb engine several weeks ago when oil broke down. I hit about 280F then. Normally I back off when they get to 260F, but the romping got the best of me and I am paying dearly for it.

I would,

make sure you are running sythetic oil

check for a lean condition at full throttle

Make sure you have the proper bypass valve in the filter pad.

Buy a larger oil cooler and/or make sure the one you have is plumbed properly and clear.

Don't let temps get over 260F

BT

formulaF302

I've got an identical situation on my port engine. I installed oil temp sending units on the remote filter adaptor and temp gauges today....but the weather went to crap before I could take them out and run them. If my bypass valve is the problem....what is the correct valve to use? The port engine does seem to be getting the oil dirtier faster than the starboard. I already cleaned the pieces of previous impeller debris out of the cooler lines, etc...but am running the stock cooling hoses with all their numerous connections etc from the adaptor on the block. My oil pressure drops to 20 lbs at idle on that engine after flogging on at 4800 rpm for awhile although the engine water temp only climbs up to 160....after idling for 5 minutes the oil pressure goes up to 40 lbs again......suggestions please....the other engine is rigged identical and seems to do just fine....

blue thunder

Formula, if you have an original mercuiser engine you most likely have the right psi oil pressure differential (bypass) valve. I changed mine out with a new one to make sure, and no change in oil temp. I believe my primary problem is one from the factory. That is, the lub system plumbing sucks. I even replaced the cooler just to see if that made a difference. None. For now I am going to keep close tabs on the oil temp gages making sure they don't reach 260F. Combine that with synthetic oil and I think I will avoid taking out more bearings. Over the winter I am planning to re-plumb both engines and get this thing right once and for all. I want 200-210 cruising. 220 after a hard romp. If I can get that, I will be very happy. Let us know what you are getting for oil temps when you find out.

BT

formulaF302

I got it out for a ride between rainstorms today and was happy with the results.....running a steady 4800 rpm gave me oil temps of 232 degrees on each engine with mobil 1 syntec blend. The sending units are in the remote oil filter unit. At cruise I was around 204 on the port and 210 on the starboard although the water temp on the port was 160 and only 150 on the starboard...cant figure that one out. When I unplane my oil pressure drops to just below 20 lbs on the port engine at 600 rpm until the oil temp gets down to 174 degrees...then the pressure climbs to 40 lbs. I'm not using any oil between changes.....so I'm guessing the bearing clearances on the port engine are just a litttle bit looser then the starboard. Is that lower pressure at idle when warm gonna make a problem later or can I live with it the way it is?????

blue thunder

Now you went and made me jeleous Formula. Those are perfect oil temps in my book. I don't think you have anything to worry about oil pressure wise. 10psi per 1000rpm will suffice.

BT

GregP

Must be a Formula thing. On my F-402 the port motor always has 10* more oil temp and 10* less water temp than the stbd. Actually, I think it's just the accuracy limit of the gauges/senders isn't any better than +/- 5-10*

-Greg