89 J70 Temp Sensor/Limp Mode

[Lord Tywin]

Overheat sensor engaging SLOW during WOT...how to troubleshoot

Finally localized an issue of WOT for 2-5 minutes causing SLOW mode on my 89 J70TLCEM. Disconnected overheat and issue goes away. Almost just bought a new one but wondered if it was actually the issue. I can check the temp of the discharge (no trailer, boat always in water) but wonder what other things I may need to look for or check. Anyone know what the temp should be or any good tips/sites? I havent found much about this particular issue. Thanks!

 

[Lord Tywin]

My 89 J70TLCEM will run all day at cruise but when I run it WOT, it drops into limp mode. Over the winter I had found the thermostat was stuck. I thought that would fix it but it didnt. Weird thing is, when it does this, the water coming out the pisser is cool to the touch. If the sensor detects an overheat condition, why would I be getting cool water? Is the sensor bad or is water possibly not making it to 1 of the 3 cylinders? Impeller? Looking for ideas or a direction to investigate.

 

[racerone]

Well the fact is that the water coming out of the tell tale does NOT go through the engine.-----A much misunderstood concept.----And please do tell , does the hose for the tell tale come off the side of the block or the top ???

 

[Lord Tywin]

Thanks for the info, I did not realize the tell tale was only to alert you that it was somewhat functioning.. I haven't had time to work on the boat as I've been putting my engine back in my SeaDoo but I ordered a new impeller kit (had boat 3 years, never done that) so even if that isnt the problem, it needs to be done. While I have it out of the water I will also check cylinder temps etc and get back with you.

 

[racerone]

You can help yourself by answering questions as in post #2 here !----I can not see , feel or hear your motor.-----Perhaps test run with a borrowed fuel tank and hose.

 

[Lakemichfish]

Are you still having this problem? On my 1990 Johnson 70, I found that the head gasket leaked allowing water to leak from the cylinder water jacket to the exhaust. The cause seems to be the head casting itself. It has a large opening that doesn't seal the gasket between the two passage ways.

 

[Lord Tywin]

OK so I have had some time to finally work on this and the tell tale comes out of the side at the bottom cylinder. I have replaced the pump but the tell tale was very very weak so I pulled the lower unit again. Seems one of the bolt holes is stripped and the big o-ring that goes on the cover doesnt fit well. I ordered a new OEM pump and figured out that a 1/4" longer bolt will hold the pump in place nicely. I was afraid I was going to have to have the hole drilled, tapped and heli-coiled but that doesnt appear to be the case. I should have her back together this weekend.

 

[flyingscott]

I dont believe your motor has a limp home mode. Does pumping the primer ball do anything when that is happening.

 

[racerone]

1989 models were the first year for the S.L.O.W.-----System I believe.----The latest water pump kit has the instructions and pieces for the cooling system modifications.-----Have your dealer look into that kit for you.

 

[flyingscott]

Well there ya go you do have it. I thought it came out in 1990.

 

[Lord Tywin]

It ended up being a poorly made pump kit. The odd shaped O ring was too big and kept it from creating a seal. Ordered a Johnson kit and it worked like a charm. Thanks for the help, and yes I can verify that SLOW was indeed on the 89 models, at least the later ones. Seems in 89 they had early and late year models which is probably where the confusion came in.

 

[Lord Tywin]

After replacing the water pump I still have the issue. I have not pulled the head off to check but I'm getting close to that as the problem persists, although not as bad as it was before the pump install. I will look into that, thanks for the reply!

 

[flyingscott]

Get an infrared temp sensor and see what the temp actually is.