Hot PCM even after new impeller, thermostat, and cooant!

[wingo812]

Help, Please!!

I have a 2004 24V with 6.0L PCM. Engine running hot (bought boat a year ago used) and wanted to change coolant and and thermostat just cuz anyway. New impeller, new thermostat and new coolant in and boat went smoothly right up to 250 degrees again. After shutting down and consulting here on tigeowners forums, I decided to back flush the raw water system in case there were impediments to water flow. After the flush, the engine will start, but won't stay running. I made sure there is fuel. I suppose it's possible that the fuel pump and or fuel relay failed coincidentally with the flush, but really??!!

Any help would be appreciated. Thanks

[Z1Fan]

Are you sure of the temp ? Are you using just the gauge or a temp gun or the such ??

[boatwakes]

HOW DID YOU BACKFLUSH IT?!!!!!!! Details, exactly how you did it. Theres a modification to the cooling system listed on here by Dom W. Forte to eliminate this common problem with high temps on those LS based 6.0L engines.

[gwhite94]

As Boatwakes said how did you flush the raw water system, I would suggest that you check the oil for water, pull the spark plugs to make sure no water got into the cylinders.

[wingo812]

For the back flush, I pulled the intake hose off the raw water housing, inserted a hose. There was a significant build up of pressure and then a big release out the pick up area grate and I jumped out of the boat and observed a free flow of water. After crawling underneath, there was some **** still in there that I was able to pull out. I then removed the other hose and did the same thing alternating release points so to speak...I removed the drain from heat exchanger and observed free flow of water and did the same thing with other drain hoses. In my mind, there now was an unobstructed raw system.

To add to the confusion, I just brought the boat home and it started and purred like a kitten but once again, I observed the temp gauge pegging full hot. So, Z1, I'm just using the gauge and haven't "gunned it".

One thing I did do was research the fuel system a bit and thought maybe I'd get a fuel pressure tester. Before going to that trouble, I ensured that the low pressure pump wires were in tact as I thought there may have been potential for me knocking them a bit from removing belt/impeller. After checking wires and unplugging and replugging in the connector was when I tried to start the motor and as reported ran just fine with the exception of the temp gauge.

I guess the next step will be to "gun" the temp as Z1 suggests...any other suggestions???

[wingo812]

If the gauge isn't faulty and the "gun" proves the same, the only thing left will be the circulation pump. How does one determine if the circ pump is bad? It certainly isn't seized up...

[Ewok]

Depending on where the boat was used, could he just have such a build up of crud in the raw water system that he isn't getting the proper flow of water through the heat exchanger causing the over temp? In the closed system, where is the heat exchanger in relation to the exhaust cooling water, if the boat is routed to use raw water to cool the exhaust manifolds and the muffler than could those parts be rusted out so bad that they need to be replaced to increase the flow of water through the heat exchanger? what about some sort of contamination in the closed cooling side, could there be some sort of obstruction to the flow through the system or the heat exchanger? What about a bad thermostat out of the box? or a thermostat that is not reading or opening up to control the flow due to some corrosion or obstruction near the thermostat? I'm not a mechanic, just trying to think of possible obstructions with the little I do know about these cooling systems.

[Z1Fan]

My next guess would be the thermostat, is it a newer fail safe type? For the lack of a better suggestion , pull out the thermostat and put in a boiling pot of water and see if it opens...if it does, you might need to have that engine and cooling system checked for some type of build up or coating on the inside passages, but a temp gun can definately help you find the so called hot spot, i wonder if one of the cylinder passages are plugged.....

[wingo812]

Does anyone happen to know where the temp that is displayed on the gauge is read? I see there is a temperature sensor "switch" on the circ pump housing and there is a coolant temperature sensor. As an experiment, I removed the coolant temp sensor wire and started motor. I got the warning beep which I haven't gotten before. Shut down engine hooked back up and restarted. Temp gauge still pegged full hot, but no warning beep and engine continued to run fine...

[Stingreye]

When I lost my serpentine belt on that motor, the alarm went off when it heated up. Is the alarm not going off even thought it's above 230?

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[Z1Fan]

If I am correct , there are two sensors one for the gauge and one for the ECM, ECM up top near the thermostat housing , gauge down on the block, left side under cylinder head

[wingo812]

No, the alarm isn't going off...