Overheat alarm ?hen cruising

[bassfish 24-7]

0D212844. S#
1993 mariner 200hp 2.5 EFI with 8inch manual jack plate.
On 1993 champion 190

My overheat alarm goes off while cruising 30 or 40MPH. Replaced water pump and dropped motor down over an inch. Since lowering motor I’m getting 12 to 14 PSI water pressure a WOT (no alarm).
When cruising or fast idling the overheat alarm will sound.

A solid beep. I shut down motor and fish for an hour. Then fire up and idle in. No alarm when I just idle - low RPM.

Any tips?
Is it possible to put lower unit on and not line up the tubes right? I wouldn’t think I could get good WP at WOT if that was the case.

[leonreno]

Could be popper valve is not opening fully or could be a gasket in water pump that is damaged. There is a gasket under the water pump base, the base is the plastic part the water pump sits on, this gasket has to be replaced regularly and it doesn’t always get done. Bad gaskets cause aeration in the water which does not cool as well.

[lpugh]

How much presure at idle?
Temp gauge readings? Temp sensor could be out of range, verifie temps with Temp gun very near both stats for the highest reading you can find, will be a little lower than actual temps, not much though
Check thermostats for proper operation, Inspect plugs and piston tops for signs of water, compression test as well

[SilverFox579]

Don always says when dealing with water pressure concerns to start at the pump and, to me, 12 - 14psi @ WOT sounds low with a new water pump. Genuine Mercury parts or aftermarket?

I agree with leonreno, if you didn't replace the pump base gasket that would be the first thing I'd do.

[bassfish 24-7]

I used SEI Marine product kit #46-96148A
i did replace the seal. I’m not mechanically that great so I guess I just need to schedule a time to take it in. I just hate to take it to the local shop because they let it sit in the boat yard for weeks until they get around to it. That’s time I could be fishing.

WP doesn’t read at just idle but if I bump the throttle a little it will read 2 or 4PSI.

i could order and try replacing water pump again. See if that works before taking it in. That’s probably my first option.

Forgot to mention that that I replaced poppet value and tested thermostats. They are working. I don’t have the other fancy tools to test temp nor do I have a temp gauge on boat.

Thanks for everyone’s input.
Very appreciated

[leonreno]

I would try a Genuine Mercury kit, may make enough difference to stop the alarm. You should have a reading at idle. What is your idle rpms?

[SilverFox579]

I would try a Genuine Mercury kit, may make enough difference to stop the alarm. You should have a reading at idle. What is your idle rpms?

+1!

[EuropeanAM]

+100... install an OEM Mercury kit (96148A8) and make sure that you replace all THREE gaskets with the correct gaskets for your engine model. Commonly see these types of symptoms with a torn gasket under the impeller plate (or below the pump base).

[bassfish 24-7]

Replaced pump and seals with mercury kit. Tested on idle only lake this AM. Had 4PSI when idle at 5mph. (More than it used to be). Tach is not reading correctly- that’s another issue that needs to be addressed. Sometimes I can knock on it and it jump down 4rpm to 2rpm.

hopefully I will get to the lake to open it up and see if PSI is better!

[leonreno]

There is a switch on the back of the tach that selects the right poles, look at yours, note what it’s on and use a screwdriver and spin it back and forth through the selections and then leave it on the previous selection. This will help remove built up corrosion on the contacts inside that can cause erratic readings.

[JOE54]

+1 always start at source w/p