2001 OX66 overheating only at speed

[Glenn B.]

Chasing this for a bit now....
New impeller, new thermostats, new poppet valve (grommet, gasket, spring and mushroom head).
Idles great, pee's great.
Run up the rpm's and temp climbs and alarm sounds.
Is it possible that the new poppet spring could actually be too stiff thereby not allowing it to open properly??
Anybody ever experience this?

[21XDC]

Makes me question the temp sensors.... I had to replace mine. They were sounding off at cooler temps than normal.

Did you replace the whole water pump with a wear plate etc or just the impeller?

[Glenn B.]

Thanks for the reply 21XDC.
Mechanic did just the impeller but all else was inspected and looked good.
I'm certainly no expert, but the temp sensor seems to be operating properly. Alarm sounds when temp gets high and sends engine into safe mode. Alarm goes away once engine cools.
I neglected to mention in my original post that, before the overheat alarm sounds after running at higher rpm's, the water pressure plummets.
Obviously something is preventing sufficient water flow at higher rpm's.
What else could be affecting that flow at higher rpm's aside from the poppet valve?
I'm going to bring it back to my mechanic, but I'm just trying to educate myself more along the way.

[CJ1]

Screen not positioned properly on lower unit causing cavitation at higher speeds. More common on HPDI lowers but something to check. Cj

[Triton Dawg]

I have had this same exact problem with mine. I will be watching your thread intently. Please keep us updated on the progress and solution.

[Skeeter Jeff]

For what its worth, my 97 175hp had a overheat alarm at high RPM only. Had great water pressure and the temp. gauge never read hot - even at high RPM's. I replaced the water pump, tstas, popit valve, temp sensors. Finally my mechanic convinced me to take of the heads and the passages were full of scale and crud, all from fresh water... this solved my problem... never expected the passages to be blocked like they were...

[cwilt]

Screen not positioned properly on lower unit causing cavitation at higher speeds. More common on HPDI lowers but something to check. Cj

This^^^

Or the pump/oring was installed wrong. Even the best mechanics are human.