I have that 500 EFI in a 2001 fountain 29, the oil is overheating really quickly, even cruising at 3500 rpm, the gauge will reach 250 so as soon as I go WOT it goes over 260 and the light come on. Now I did cleaned up the oil cooler, nothing changed. I did bypassed the fuel pump cooler so the fresh water goes directly from the fresh water pump to the oil cooler, no change. Now I don't know where to look anymore, oil pressure is good, the motor doesn't overheat at all. What next??? and it seem to get worst as I use the boat trough out the summer.

Have you verified the oil is actually overheating? Are you sure you don't have a gauge problem? With pressures and water temps normal, I'd rule out the gauge first.

Thermostat in oil cooler

backflush oil cooler also

im not expert but...is the merc smartcraft buzzer going off? if not, its likely a bad sending unit or bad guage. if thats the case, your engine oil temp is actually normal but gauge is reading incorrect.

if you have ruled both of those out...agree with vettex, might be thermostat in oil cooler.

The HP500 EFI is not a SmartCraft motor. It has the MEFI3 ECM and the oil temp sender does not feed any logics, only the gauge.

I would recommend confirming the temp and if confirmed high I would check the thermostat.

I didn't know that there was a thermostat for oil!! I just found out the location on the schematic. I will do the gauge check first and if nothing change I will change the thermostat. Pretty sure it's the thermostat, I did touch the cooler when the gauge was showing over heating and you could not leave your hand on that for 1 sec. Thanks for the info guy's!! really appreciated.

You can use an infared hand held and shoot the oil lines and oil filter. You do have an oil thermostat, it is mounted in a housing where the oil filter would be on a stock block Chevy. You can pull the ends off of your oil cooler to see if it is clogged. We run in mud slit bottom river, we need to clean ours on occasion.

The thermostat is in the oil filter housing mounted to the 1-7 bank head. It's not in the adapter on the block pad

This is what I found on the schematic and this is how it is on my engine : number 17.... http://www.boats.net/parts/search/Me...ne)/parts.html

seems to me that it is in the housing where the oil filter would be on a stock block