Mercruiser 5.0 Running Hot at Idle Even After Many Component Change PLEASE HELP!!!!

[gonzalez3346]

Hello Everyone,

I have a 23 Sea Ray Sundancer I/O Mercruiser 1994 5.0 V8 Serial Number 0F132208. Last season my temperature gauge started to raise at idle and as soon as I open the throttle the temperature will go down to normal operation (160-170 degrees). I then used an IR temperature gun to see if I had a problem with my raiser and or manifold. (Everything checked okay). I decided to replace my raw water impeller at the out drive unit thinking that that was the problem. Well the impeller was okay and the problem persisted. I ran the entire last season with the problem since my engine was operating at the normal temperature based on the IR gun. Of Course I did not let the temperature raise over 175 by either opening the throttle or just turn the boat off (Remember the problem is only at idle).

This season I decided to tackle the problem and started by replacing the raiser and manifold just as a prevented maintenance. They both were in good condition but swap them anyway.
I also replace the Thermostat with a 140 degree as suggested by the manufacturer.
I also replace the temperature sender electrical component.
I also back flushed to see if the Power Steering cooler was clogged (was okay and not clogged)
I also check all my hoses looking for and obstruction (no obstruction found)

After all this component change and triple checks I found no problem but the temperature continues to rise over 180 going into 210.
Again I used the IR gun and the riser, manifold, temperature sender, thermostat and all hoses read at normal temperature or between 140-150 degrees.

I did notice that the circulating water pump was reading in the IR gun at about 170 to 180 degrees I do not know if that is a normal temperature for the water pump. (The boat was running for about 10-15 minutes connected to a water hose)

What else can be causing the temperature to rise? Can it be the circulating water pump or even the temperature gauge? How to check those are okay? I already spend over 1k trying to pin point the problem with no luck...

Please help! Any recommendation?

Thank you all...

 

[Bondo]

Ayuh,.... Welcome Aboard,..... Does yer t-stat housin' have the check-balls in the ports goin' to the exhaust,..??

 

[DaboatnutinWA]

Had a similar issue with my 4.3L but temp at idle was good. Would get hot up on step. I removed the thermostat housing and found one of the check balls was corroded shut and wouldn't move. I soaked the housing in Evapo-rust, put in a new thermostat and everything seems fine.

 

[gonzalez3346]

No, the thermostat housing does NOT have the balls. Believe me that was my hope.

 

[thumpar]

Did you actually remove the power steering cooler hoses to check or just backflush? I have heard where an old impeller will break apart and pieces get lodged in there and backflushing will not get them out. It needs to be dug out.

 

[gonzalez3346]

I did removed it and also back flushed. Not to mention that my old impeller was in good condition when swapped.

 

[duped]

Outdrive's water hose kinked? Usually that's an issue that turns up after a bellows job if the hose isn't cut to the correct length, but I have also seen it happen when the hose gets old and loses flexibility, or slips off a bit and thus becomes "longer".

 

[NHGuy]

Yes,check the hose that goes from the back of the bellhousing to the transom plate. It has to be a very precise length and not twisted. Also check inside the upper drive where the impeller housing output tube fits into the water pocket cover. If it's been run hot those pieces can be heat warped and not have good seals. The leaking water wouldn't cool the engine enough at low speeds and could do a bit better as the rpms come up.

 

[alldodge]

Hello Everyone,

I have a 23 Sea Ray Sundancer I/O Mercruiser 1994 5.0 V8 Serial Number 0F132208. Last season my temperature gauge started to raise at idle and as soon as I open the throttle the temperature will go down to normal operation (160-170 degrees). I then used an IR temperature gun to see if I had a problem with my raiser and or manifold. (Everything checked okay). I decided to replace my raw water impeller at the out drive unit thinking that that was the problem. Well the impeller was okay and the problem persisted. I ran the entire last season with the problem since my engine was operating at the normal temperature based on the IR gun. Of Course I did not let the temperature raise over 175 by either opening the throttle or just turn the boat off (Remember the problem is only at idle).

This season I decided to tackle the problem and started by replacing the raiser and manifold just as a prevented maintenance. They both were in good condition but swap them anyway.
I also replace the Thermostat with a 140 degree as suggested by the manufacturer.
I also replace the temperature sender electrical component.
I also back flushed to see if the Power Steering cooler was clogged (was okay and not clogged)
I also check all my hoses looking for and obstruction (no obstruction found)

After all this component change and triple checks I found no problem but the temperature continues to rise over 180 going into 210.
Again I used the IR gun and the riser, manifold, temperature sender, thermostat and all hoses read at normal temperature or between 140-150 degrees.

I did notice that the circulating water pump was reading in the IR gun at about 170 to 180 degrees I do not know if that is a normal temperature for the water pump. (The boat was running for about 10-15 minutes connected to a water hose)

What else can be causing the temperature to rise? Can it be the circulating water pump or even the temperature gauge? How to check those are okay? I already spend over 1k trying to pin point the problem with no luck...

Please help! Any recommendation?

Thank you all...

I think you need to look at your circulating pump. Wouldn't be the first time the impeller is loose and starting to spin freely on the shaft

 

[gonzalez3346]

Do you guys think is the temperature gauge?
At what temperature should the water pump should be running if I measure it with the IR gun?

 

[alldodge]

The engine pump tries to move water into the block, if the thermostat is closed, most water moves to the exhaust. When thermostat opens more fresh water moves into engine. My guess is the circulating water pump should never reach 170, maybe 140 - 150

 

[gonzalez3346]

I guess the most concrete advise here is to replace my water pump. Is there a way to check if it's working properly? Based on all my test that seems to be the area that shows higher temperature range based on the IR gun.

 

[gonzalez3346]

I am thinking if the sending unit is reading the correct temperature with the IR gun why would the gauge will show a different temperature? The gauge should show what the sending unit is reading correct?

 

[alldodge]

I guess the most concrete advise here is to replace my water pump. Is there a way to check if it's working properly? Based on all my test that seems to be the area that shows higher temperature range based on the IR gun.

Maybe, I would pull the pump and remove the rear cover to see if the impeller is the issue. If it is, get another pump, if not need to look further. Gaskets are cheap, but it does take some work.

I am thinking if the sending unit is reading the correct temperature with the IR gun why would the gauge will show a different temperature? The gauge should show what the sending unit is reading correct?

It should show the same but auto/marine gauges are not that accurate most of the time. It is all give or take 10 percent. There are better gauges but they cost more. What your seeing is an issue, not so much with a gauge reading, its more an over temp issue

 

[NHGuy]

You can verify the gauge accuracy by taking temps of the sender. It's in the thermostat housing.