Engine overheated, really frustrated.

[gregski]

You want to measure the resistance (ohms or Ω). The sender has one wire, so you measure between that and a chassis ground point. The basic idea is that it should be high resistance when cold, something in the 1000's of ohms and lower resistance when hot. Normal operating temp might be somewhere around 500Ω.

[gregski]

Just an update, ran a compression today this AM and all cylinders are within 123-132 which makes me feel a lot better! Also plugs looked good.

Fortunately, there are lots of ways for the temp sender/gauge to go haywire, read like its overheating and put you into the limp-home mode which don't actually involve the engine overheating.

[jmb]

I had an impeller hub let go from the rubber and only he brass part was spinning. I cranked the boat over while watching it. You may have to have someone else crank it while you watch. My .02 worth

[Kennyk69]

A good way to understand the severity of a "thermal event" is to check the inside of the 90 degree elbow on either of the manifolds.....if you were not pumping water for an extended period the inside will be burnt/melted. They get brittle after being so hot and will fail - as in pop right out of the manifold flooding the engine top down with water.
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[icemanftr]

Just an update, ran a compression today this AM and all cylinders are within 123-132 which makes me feel a lot better! Also plugs looked good.

Seems pretty low, but consistent. I would maybe check for a leak down test. My compression is a good 180-190.

[crr1876]

Yea I figured out I didn't do my compression test exactly right. I only removed 1 plug at a time instead of all 8 at once and I didn't have the throttle wide open, just up at 90 degrees. I don't necessarily think it's worth testing again since they were all very close to each other and above 100 but others might not agree.

[parrothd]

Not all gauges are the same, they will give different readings. The important thing is that all cylinders are in the same psi range within 10%.

I think your over worrying, take the boat out and see what happens. If you overheated it too lockup, then you've got problems your not going to do more damage by running it..

[crr1876]

Not all gauges are the same, they will give different readings. The important thing is that all cylinders are in the same psi range within 10%.

I think your over worrying, take the boat out and see what happens. If you overheated it too lockup, then you've got problems your not going to do more damage by running it..

I definitely agree with you. I'm swapping in a new thermostat and water pump then I fully intend to go run the boat!

[crr1876]

Just an update, I replaced both water pump and thermostat, got everything back together and ran the boat on the fake a lake. It ran great in the yard heating up to 180 then watched the temp gauge as the thermostat would open boat would cool to about 170 or so. I ran the boat over 30 mins with some good revs in neutral and it never once overheated.

Bad news is after I killed the motor (but had left perko switch on) as I was cleaning up tools etc, about 2 hours later I happened to glance at the temp gauge and it was pegged again over 240!!! I immediately turned the key to accessory position and the gauge went back to far Left instantly. This leads me to believe I actually never had a true overheating problem but actually have some kind of electrical or sensor type problem. This fits hat happened on the lake cus my wife had shut down the motor while I got back in the boat and put my gear away. Unfortunately I'm kind of lost as to what to do next, idk if I should just take it in and let the professionals take over?

[zabooda]

I wouldn't fret none. It appears you have bleed through your temperature gauge from one battery to the other battery (floating ground) that clears itself with the 12 volts applied to gauge. The changes you see is probably from the RTD dropping resistance as the engine cools off and allows the current to increase (talking mA). It leads me to believe the Perko setup needs to examined but check the grounds as they need to be tied together.