knock sensors, head gaskets, overheating. The best overheating mystery of all time!!

[TAC]

Ok guys this is gonna be a long one but there is a lot to explain. So here's the deal. I have two 2009 gtx 155 NA machines both with around 1500 hrs. Yes thats right 1,500 hard lived hours. Both at the same time started having overheating issues after WOT getting P1116 engine temp codes. I assumed it was head gaskets so I changed the head gasket in both with OEM gaskets and new stretch bolts. Both had no change. I decided to focus all my effort on one machine to find the problem being that both had the exact same symptoms. I installed a colder thermostat thinking it was getting stuck. No change. I replaced all the hoses from ride plate and the hoses to the oil cooler, flushed both ride plate and oil cooler and replaced the coolant cap. No change. I pressure tested the cooling system at 15PSI and no leaks detected. I have replaced the temp sensor on the block twice, and exhaust twice, no change. Convinced it was the head gasket and wanted to get the machine going for 4th of July I just so happened to have a brand new SBT block built and sitting in my garage so I installed that. After breaking it in for about 5 hours I began opening it up a little more aaaaannnnd it overheated. So theeeeeeen I started thinking the knock sensor was bad causing combustion temp to rise causing the over heat so I grabbed a used knock sensor I had sitting around and replaced it no change......THIS is where it gets weird.....ready........I tested the resistance through the knock sensor it was around 4.85M perfect, then checked the wires to the computer.....alllll good. To test the Computer I unplugged the knock sensor and revved the machine past 5k in comform to the shop manual and there was no check engine light....hmm that's odd the knock sensor is UNPLUGGED and the computer doesn't know it. Swapped with a working computer i had sitting around, tested again...no check engine light. So I happen to have an extra A side wiring harness sitting around with low hours so I replaced the harness and revved the engine past 5k and bingo check engine light P0326 knock sensor out of range. Awesome......so I figured it was safe to assume that the computer was not reading the knock sensor but with the new harness now it was, so I hooked up the new sensor and harness took it for a drive and FUUUUUCK. OVERHEAT. So now I went back to the other ski the one I only replaced the head gasket on. I revved it up past 5k with the knock sensor unplugged and just like the first ski there was no check engine light. I swapped the A side wiring harness with the extra I had and now get a P0326 if I rev past 5k with the sensor unplugged........so I'm thinking. Could the sensor not working have caused the head gaskets to fail from overheating? Is this weird thing with the wiring harnesses related to my overheat problem. How the **** did the computer on both machines not realize the knock sensor wasn't plugged in on the original harnesses.......any ideas what is causing this overheat?? By the way coolant is not boiling or leaking from the system on the overheats and idling for 15-30 seconds brings the temp down. It also doesn't overheat at WOT, it is when you come off WOT or if you stay around 5k and are cruising.

TL : DR
Two skis both 2009 155 na. Both overheat. Replaced head gaskets, sensors, hoses etc no fix. Even replaced one whole block. Still overheat. Found that both machines had bad wiring harnesses to the knock sensor but never threw a code. What can I do, replace head gasket again? Did the bad harness to knock sensor kill my engine.

 

[ski-d00]

Do you mean p-0116? This is faulty temp sensor, not really overheat. Have you changed the temp sensor itself? It doesn't sound like it is really overheating. It just thinks it is. Do you have any leaks? What you describe does not sound like a head gasket problem. You flushed the ride plate but does it have good flow through it?

 

[TAC]

ski-d00, I replaced the engine temp sensors 2 times, I also pressure tested the cooling system at 15 PSI for 3 hours no leaks. Ride plate has great flow and there is no sign of any type of corrosion. Also I recreated the condition multiple times on both skis, for sure P1116 engine overheat.....

 

[ski-d00]

Is it really overheating? The temp sender won't trigger overheat until boiling point so typically overheat is pretty obvious with bubbling and overflow from the coolant tank. You can plug in a spare temp sender and not install it so the temp never reaches boiling point to test, just let it lay on engine so it only gets warm but be careful since it can overheat and not sense it.

Pressure testing the system is not really an issue, flow testing the system is. A partial blockage somewhere will do exactly as you describe. Water pump impeller needs to be working properly as well for good flow.

 

[TAC]

I installed clear hoses briefly monitor flow and make sure the thermostat was opening. Flow looked good. Water pump fins were good. I'm going to try dumping some CLR in the ride plate to clean any deposits. The lake water is usual around 60 degrees F. I checked the manual and it says the overheat alarm will activate at 212F, I figured with the system under 13 PSI pressure the boiling point of the coolant would be around 250F so the engine could still overheat without boiling.

 

[Coastiejoe]

Seadoo updated the temp sensors as they fail all the time. Replace them to eliminate them from being the issue.


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[TAC]

I have replaced both temp sensors on block and exhaust 2 times already

 

[ski-d00]

With 60 deg lake water, you will have plenty of cooling through the ride plate as long as the flow is good and the t-stat should cycle frequently. Actually, the boiling point will be over 270 due to the 50/50 coolant mix but this higher temp will build higher pressure which then gets the system over the 15psi which you end up with a boiling over tank bottle.

Sounds like you need to know the temp if it is actually overheating or not. Newer models give this info right on the dash as a display option.

You are running 50/50 mix, correct? Some people seem to think more antifreeze is better and they couldn't be more wrong. Most racers use nearly straight water because it removes more heat.