HELP! Engine overheating....

[JimG]

In my old Trojan flybridge! Right after I bragged about how reliable it was!

I'm totally stumped... here's the deal.

It's a 1979 Chrysler 318 225hp, 1200 hours. Raw water cooled, 140 degree t-stat. Has ALWAYS run 130-140 degrees. Went out last Saturday, no sweat. On the way home, at 2800 rpm, see temp rising. Goes all the way to 180, then spikes to 200 when I idle it down. Slowly comes back down at idle.

Here's what I've done so far: changed raw water impeller, cleaned oil cooler tubes, boiled out risers/elbows, replaced t-stat, replace sending unit. Took her out yesterday. Plenty of water out the exhaust. Cool at idle. Shot temps:
Manifolds: 100
Risers:95
Intake:130
Block: 112

Ran up to 3000 rpm, within a mile I was at 180. Shot temps:
Manifolds:120
Risers: 110
Intake: 166
Block:146

TONS of water flow out of the exhaust. Pulled hoses on the engine: lots of water flow out of the block. Hooked up a garden hose to the top of the circ pump, lots of water passing through the block.

It's definitely in the block circuit, and not in the exhaust manifold circuit. Something is impeding flow in the block. Could my circ pump be dead? I'm hearing no racket from it, nor seeing leaks. Can the shaft break or the impeller come off? I've been told that the circ pumps on these rarely fail, but I'm running out of ideas.

Thanks!!

JimG

[MOP]

Jim I can explain the spike, when you throttle back to idle after a run the hot water rises in the block due to the slow circulation and the gauge goes up after a few minutes it goes back to normal. But from your gun readings the sender or guage is Whacked. It would overheat very quickly with a bad circ pump, yours is fine.

[JimG]

Thanks M.O.P! I ran it today w/o the t-stat. Same thing, just took longer! Saw 180 on the guage, gun read 181 on the rear of the intake manifold. Exhausts cool, plenty of water. Engine's running great, BTW!

Could there be a blockage in the intake manifold water passages? The front of the manifold reads 140, the rear reads 181.

Still stumped!

JimG

[Ralph Savarese]

Sounds like a circulation pump problem the raw water pump will be enough to cool the front half .I would check circulation impeller. I have seen where people use automotive pumps and the impeller rots off!
Ralph

[MOP]

Chrysler circ pumps do spin the impeller on the shaft. Good call Ralph!

[JimG]

You guys were dead on!

The shaft was sheared off at the impeller. The impeller was just laying in the housing. Put a new pump on, and VOILA! It's fixed!

Thanks for the input!

JimG