1981 Johnson 90 HP overheating, but not all the time

ranger335 · Saturday at 10:23 AM

Ongoing/intermittant problem for over a year. Replaced the impeller (twice), thermostats and flushed out the heads and or block using a water hose hooked directly to the hose fittings on the blocks. That was last year. This year I replaced the inlet screens and re flushed. Thought I had it, but no. Did a vinegar and dawn flush like I saw on YouTube with the lower unit in a barrel. Thought I had it, didn't run hot and I ran it for quite a while at full throttle. Took my farmer buddy fishing and never made it to the river, ran hot on the 1/2 mile run in the creek. This morning I removed both heads and there was very little corrosion or anything that would cause a blockage. I don't understand about the water diverters. Mine appear to be swollen but if they are supposed to divert the water why does swollen matter? I have to order new head gaskets anyway, so I'm going to order new water diverters also. PLEASE HELP, the white perch are biting.

racerone · Saturday at 10:29 AM

removed the covers on the heads?

ranger335 · Saturday at 12:55 PM

racerone said:
removed the covers on the heads?

Yes. Last summer. All seemed to be good. This morning I left them in place. gaskets are cheap though, I can remove them if you think it will provide some insight.

jimmbo · Saturday at 1:26 PM

Have you verified that the Overheat Sensor is functioning properly?

ranger335 · Sunday at 5:39 AM

jimmbo said:
Have you verified that the Overheat Sensor is functioning properly?

No, but that can be my project for later today.

Berdink · Sunday at 6:41 AM

Have you tried pointing one of those cheap heat sensing guns at the cylinders to see how hot it actually is?

Berdink · Sunday at 6:42 AM

I'm guessing it's too hot to touch?

ranger335 · Sunday at 6:50 AM

Berdink said:
Have you tried pointing one of those cheap heat sensing guns at the cylinders to see how hot it actually is?

Yes, 180 something and 165.

ranger335 · Sunday at 6:52 AM

Berdink said:
I'm guessing it's too hot to touch?

I have welder fingers, so I'm not a good judge.

ranger335 · Sunday at 6:59 AM

After I looked at several pictures on here, I think I figured out the water diverters. They make the water go vertical, not horizontal. If so, mine are fine.

racerone · Sunday at 7:02 AM

I suggest you replace the 4 ( 2 per side ) diverters.

ranger335 · Sunday at 7:05 AM

racerone said:
I suggest you replace the 4 ( 2 per side ) diverters.

Can you explain what the diverters do? I don't have a problem with replacing them, I just want to understand.

JustJason · Sunday at 7:57 AM

They serve 2 purposes.

First is they force water around the cylinder walls to allow for even cooling of the cylinder walls (IE 1/2 of the cylinder wall doesn't cool twice as fast as the other 1/2 of the cylinder wall).

They also act as a restrictor to slow down the flow of water through the engine and outside of the cylinder walls so that the water has time to absorb the heat, which it can not do if it's going to fast through the engine.

racerone · Sunday at 8:09 AM

They guide water through the water jackets.----And nothing to do with the speed of the water. ---Make sure to install head gaskets correctly.

ranger335 · Sunday at 2:02 PM

I removed the water covers, no blockages. I tested the heat sensors one grounds at 180 and the other a hair over 200. I can't seem to find a definitive answer to at what temp they should ground.

ranger335 · Sunday at 2:12 PM

I think I've found the intermittent part of my problem. I retested the sensor that sounded at 180 and it went to just over 200. Gunna try again and report back.

Berdink · Sunday at 2:33 PM

Thanks for sticking with it, posting your progress, and saying you'll report back.

ranger335 · Sunday at 2:43 PM

I'm just sitting here sipping a cold one and testing my heat sensor. Got 200 again and then this, twice.

1981 Johnson 90 HP overheating, but not all the time

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