280 running hot but cools down at idle

[C10]

Check it out, feel like this is simple but driving me bonkers!
Stock 280 runs up to 240ish midrange and will not cool back down below 210 unless i stop. I changed the obvious being the water pump and checked the pick up tube. Thought my problem was solved running wot at 140 but after a few hours running hot again.
I have rechecked housing gaskets,water pump,pick up tube and it seems good. 5 psi is all i see. Pretty sure i saw 10 psi the few times it ran 140. Sorry to bore you,but chime in please on any ideas. Thanks

[C10]

Sportmaster case btw

[90 5.0]

Check the rubber gasket where the water tube goes into the water pump housing. Had one do exact same thing, gasket wasn't sealing on the watertube was blowing water out at rpm

[C10]

That was my first look thinking the plastic tube that joins the cooper tube and housing slipped off but its siliconed on qhich i have never had to do.. What rubber gasket are you referring too? The one that slides down the driveshaftand rest on top of water pump? Thanks for your reponse man

[90 5.0]

That was my first look thinking the plastic tube that joins the cooper tube and housing slipped off but its siliconed on qhich i have never had to do.. What rubber gasket are you referring too? The one that slides down the driveshaftand rest on top of water pump? Thanks for your reponse man

The plastic tube is only a guide tube to help line up the water tube and the housing during installation. You don't even really need it, below that tube should be a rubber gasket that goes into the base of the water pump housing before the plastic tube goes on, this is what actually seals around the water tube, if that is not there that is 100% your problem. At idle enough flow goes up the tube to stay cool when rpm goes up it blows out around the water tube instead of forcing all the water up it.

An easy way to tell is to put a hose on the LU and see if tons of water is blowing out through the exhaust and barely any coming out the dumps.

[C10]

Ill drop it again, yes ive notice water spitting out my exhaust aanzd have to crack the throttle on a hose to make it piss, but never spent much time on a water hose to know whats not normal. If i can figure out where this rubber gasket dissappeared to i bet itll solve my problem! Thanks for your time bro, big help!

[tomoad]

Check the rubber gasket where the water tube goes into the water pump housing. Had one do exact same thing, gasket wasn't sealing on the watertube was blowing water out at rpm

Yes check rubber gasket where water tube is at base of pump. Mine didn't exactly as you described. I somehow got the gasket folded in half blocking the flow.

[C10]

Well i never noticed that rubber gasket for the pickup tube inside the housing but it is there and seems fine. Same results becoming frustrating or maybe im just stupid! Idk

[C10]

Okie doke, thanks for the ideas and will find someone local hopefully trust worthy to figure it out.

[Bruce2]

I would check the poppit valve to see if it's stuck open, if it has one.

[C10]

I would check the poppit valve to see if it's stuck open, if it has one.

I checked it already it does not