Overheating 454
 

I have 9 hours on a rebuilt 454. I have NEW exhaust manifolds, Risors, and mufflers. Impeller is new as well as changing to the one piece housing.

Idle is fine and runs strong (normal operating temp.) Increased speed and long trips tend to send temp. rising. When temp. reaches close to 200 degees I can slow down and speed up again and temp. will fall. Seems as though it is a flow problem. Any suggestions as to what is next for me?

Additional info.
Bravo one outdrive
160 degree TStat. NEW.

there are alot of things it could be but take the themo out and install a 140* if you need one and the impellar could be going bad even being new .I would take out the thermo first ! do you have a cross over or pump ??

I've found that an newly rebuilt engine will run cooler after is is broken-in (>25hours)

Pump I beleive. What do you know about the check balls in the thermostat housing?

Did you ever figure it out?

I have the same problem with a 502 mag efi.

New impellars but haven't tried the 140* stat yet....

I had the same problem.

It was 2 things. The minor one was that the hose that runs from the outdrive to the raw water pump had collapsed internally. So when there was suction, the hose would just close off. When I took it off and held it up you could see blisters, but not big bumps. I cut it it to little pieces and you could see that the blisters would be almost the size of the hose.

The second cause and a MUCH greater part of the problem was that the tube that runs though the bell housing to the drive was collapsed at the very end. The end inside the boat. I took the housing off. The one that has the two 7/16 bolts to hold it on. The hose is made out of hard plastic. The very end was crushed like some one hammered on it. I took a dremel with a 90* angle on it and bored the end of the hose back to an unrestricted size.

Gene Bopp

nor should you try it the 454/502 mag efi use a 160 degree stat and normally run 160-180 and usually pretty steady/solid if not you have another problem, maybe a bad stat, blockage etc. The 140 degree stats are for carb engines not efi's,, if you put in a 140 the pudr will run it in rich start up mode until it warms up which of course it never will.

Thanks for the heads up on the 140 stat.
Do they make water pressure gauges that can be inserted inline and check the water pressure after the pump so I can rule them out. My one engine runs rock solid 175 dg. The other runs does the same until I push it over 3500 rpms then it climbs to around 200dg. When I slow down the temp drops.

Is there a way to do a pump check by unhooking the hose from the engine then start the engine and check how much water comes out in a minute?

TIA