Engine Cooling

[Triple502]

I recently replaced a 1995 Mercruiser 5.7, 260 hp motor with a new long block. Motor seems to be fine except that it is running a little warmer than the specs call for. I replaced the T-stat (165 deg) twice and put on new impeller and pump housing. After all of that I still get the same reading on the gauge, 185-195. The only other thing I can think of is the power steering fluid cooler or the sending unit. I should note that before the old motor locked up, it never went above the 165, so that leads me to believe the intake hose is fine. The manifolds and risers are brand new as is the circulating pump on the motor. I did reuse the intake manifold but had it checked at the local machine shop and it was given a clean bill of health. Anything else? The boat is in the water now and the 5.7s are mated to Bravo II drives. Is 195 too hot? It never goes above that temp and I am operating in brackish water in southern MD. Thanks.

 

[bman440440]

do you have a closed cooling system on it? have you checked for "bravoitis"?

 

[Triple502]

Sorry, should of mentioned it's raw water cooled. As for the "bravoitis", the old motor never ran this hot which leads me to believe this isn't the issue. But for argument sakes, does the boat need to be out of the water to complete that job if I decide to do it? Next time I need to replace a motor, I am paying someone to do it. :facepalm:

 

[alldodge]

Yes boat has to be on the hard to check and or repair for Bravoitis. Yes, 195 is to hot for a boat motor.

Get an IR temp gun and go around the motor noting where the hot spots are. It might be your gauge, sender or may really getting hot. As for the old one never got above 165, it could also be the old motor had a tad bit less compression so therefore less heat was being generated

 

[Triple502]

I went down today with a Fluke temp gun. I took measurements all over the motor and the hottest reading on the port head was 152 degrees. At the thermostat housing it was 142. So I went for a ride and had the misses operate while I took measurements. I took measurements on the new motor (port side) and compared them to the starboard motor, taking measurements in the same places. I was relieved to learn that the measurements were never more than 5 degrees different so I am thinking it's the sending unit or gauge. I will make up some jumper wires and swap gauges to confirm. What do you guys think? The temp gauge was reading 190 while the fluke was at 150. I appreciate any and all feedback.

 

[alldodge]

I don't think you have a heat problem, just a gauge/sender problem. The IR gun works very well, so you don't have an over heat issue. Swapping the gauges will let you know if its the gauge or the sender

 

[Triple502]

Alldodge, I took IR measurements on the heads, thermostat housing, intake manifold, front of the block and risers/manifolds. Is that sufficient or do I need to climb down in the engine room and check the block from underneath? Really don't want to be down there while running if I don't have to. Thanks.

 

[alldodge]

You should be good, what was the thermostat temp compared to the gauge reading?

 

[Triple502]

On the t-stat housing I never got a reading higher than 152 but the gauge said 190-195. I am going to try and get down there in the next couple of days with some jumper wires and swap the gauges to see if it is a sender or gauge. Thanks for the quick reply!