600SCI Overheating Help

[JD D05]

Ok so here is what is going on. Motor ran flawless all last year, first trip this year on the dock to launch it has a bad impeller housing had a spare and drop it in. Didn't notice in major issues with the old impeller. Out on the lake that same engine is over heating at idle but makes more psi than the other engine. Get back home and flush the system thinking maybe we missed something etc. Run it on the hose and it does not get warm. This last weekend it is still overheating on the lake...

If I bump the RPM's up to about 1400 it holds and sometimes goes back down. Once I get on plane it instantly drops down to normal operating temp. Water pressure varies but under power it seems to be making a little more pressure than the other engine and it has always run about 8 degrees hotter also.

This is one of those issues that you just start guessing which is really annoying...Any ideas? Thermostat maybe?

 

[McKay]

Jared, doubt it’s a thermostat as that system is closed. Would think there is a blockage on the raw water side somewhere since you are seeing more pressure than your other engine. Just a guess. Did you chase around all the raw water side of things and look for something stuck in one of the heat exchangers?

 

[Riverfamlee]

I think those still have the heat exchanger? Did you check those gaskets to make sure they are still intact? Had a similar issue with the 496ho and the gaskets feel apart and clogged the heat exchanger.

Just a thought. Not an engine dude by any means

 

[JD D05]

Jared, doubt it’s a thermostat as that system is closed. Would think there is a blockage on the raw water side somewhere since you are seeing more pressure than your other engine. Just a guess. Did you chase around all the raw water side of things and look for something stuck in one of the heat exchangers?

Yes the entire system was flushed. At idle the motor overheating is at about 2.5 PSI.

 

[McKay]

So if memory serves it has 4 heat exchangers, fuel, oil, power steering then the main exchanger up front. Hits the 3 smaller ones first if I remember right.

Two I think are down low below the headers than one up high on the rear. Sometimes the rubber gaskets on the front snd rear where out and suck in and can block water. I think we changed those on the main heat exchanger on the front? Don’t recall if we did the back.

 

[McKay]

Yes the entire system was flushed. At idle the motor overheating is at about 2.5 PSI.

I would question how they flushed it? Read my above post about the rubber end cap gaskets.

 

[JD D05]

So if memory serves it has 4 heat exchangers, fuel, oil, power steering then the main exchanger up front. Hits the 3 smaller ones first if I remember right.

Two I think are down low below the headers than one up high on the rear. Sometimes the rubber gaskets on the front snd rear where out and suck in and can block water. I think we changed those on the main heat exchanger on the front? Don’t recall if we did the back.

We did do the front but don't think we did the rear. I also checked the gaskets on the main exchanger and they were fine.

 

[Shlbyntro]

The front main is the only honeycomb cooler, all the others are straight flow through and should not create any kind of blockage.

I'd double check all the clearing work in the cooling system. Older bravo transom assemblies, if thats what you have, are known for building up a restriction where the water intake hose goes through the transom plate. That would be my next place to go once cooling system is verified ok from after the flush and impeller/housing are verified ok. You could also have an airleak on the suction side which would include everything up to and including the water pump housing and impeller

 

[JD D05]

The front main is the only honeycomb cooler, all the others are straight flow through and should not create any kind of blockage.

I'd double check all the clearing work in the cooling system. Older bravo transom assemblies, if thats what you have, are known for building up a restriction where the water intake hose goes through the transom plate. That would be my next place to go once cooling system is verified ok from after the flush and impeller/housing are verified ok. You could also have an airleak on the suction side which would include everything up to and including the water pump housing and impeller

Thank you

 

[Teague_JR]

The front main is the only honeycomb cooler, all the others are straight flow through and should not create any kind of blockage.

I'd double check all the clearing work in the cooling system. Older bravo transom assemblies, if thats what you have, are known for building up a restriction where the water intake hose goes through the transom plate. That would be my next place to go once cooling system is verified ok from after the flush and impeller/housing are verified ok. You could also have an airleak on the suction side which would include everything up to and including the water pump housing and impeller

The oil cooler on the rear of the engine as well as the power steering cooler on the port side of engine are also "honeycomb"

The water pressure sensor is at the water inlet of the engine oil cooler on the rear starboard side. You might have impeller blades wedged in there so good they arent dislodging with a back flush. Pull that end cap..

ALSO It could be a bad thermostat. FYI They have a diverter plate on the bottom that is necessary or coolant will not circulate into the heat exchanger properly.

ALSO I would never change a sea pump housing without putting in a new impeller. not sure if I read that right

 

[Shlbyntro]

The oil cooler on the rear of the engine as well as the power steering cooler on the port side of engine are also "honeycomb"

The water pressure sensor is at the water inlet of the engine oil cooler on the rear starboard side. You might have impeller blades wedged in there so good they arent dislodging with a back flush. Pull that end cap..

ALSO It could be a bad thermostat. FYI They have a diverter plate on the bottom that is necessary or coolant will not circulate into the heat exchanger properly.

ALSO I would never change a sea pump housing without putting in a new impeller. not sure if I read that right

Good note. Been a while since I had a 600. Very rarely do I find any honeycomb coolers aside from the mains on mercruisers. Im willing to bet you see those a bit more regularly than I do tho. Id defer to you're knowledge off hand on this one without scouring the parts diagrams

 

[JD D05]

The oil cooler on the rear of the engine as well as the power steering cooler on the port side of engine are also "honeycomb"

The water pressure sensor is at the water inlet of the engine oil cooler on the rear starboard side. You might have impeller blades wedged in there so good they arent dislodging with a back flush. Pull that end cap..

ALSO It could be a bad thermostat. FYI They have a diverter plate on the bottom that is necessary or coolant will not circulate into the heat exchanger properly.

ALSO I would never change a sea pump housing without putting in a new impeller. not sure if I read that right

Thanks !!! It did get a new impeller.

 

[FROGMAN524]

When you say overheating what temps are you getting? My motors run 135-145 no matter what. Idle or WOT. Pressures are different between the two by up to 5PSI as well.


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[JD D05]

When you say overheating what temps are you getting? My motors run 135-145 no matter what. Idle or WOT. Pressures are different between the two by up to 5PSI as well.


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180

 

[FROGMAN524]

180

So my port motor did that last fall, actually last damn dam run, it got to 175-180.

As it turned out my oil cooler was clogged up with debris from a failed rubber gasket. Now it’s same as starboard motor.


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