Got to the lake with my project and one MTR overheats until I Rev it then it pumps enough water to turn off the alarm and cool it down(same thing in the driveway). I had everything apart and checked the impellers,,,,so,did I burn up the impellers in the driveway with the muffs,,,, or is it possible to get flow with the inlet/outlet reversed and still pump some??? Air pockets from a fresh/dry mtr??I'm lost,again.

Might have old impeller parts stuck in the cooler. Remove the outlet line from the pump and remove the incoming line from the stat housing. Backflush with full garden hose pressure and flow. Chunks of rubber coming out says you had an obstructed cooler.

Hey there, I remember you
Cooler being?? oil/power stearing cooler?

Whichever is the 1st one after the seawater pump is what you are looking for. More than likely it will be the oil cooler.

So is it impossible to be pumping any if I reversed the hoses?What is the normal rotation on BBC?RH?

LH rotation is norm? correct????
Took the SW pump off and washed backward like you said Mcollinstn. Didn't see anything big just rust and such. Impeller is all there,seemed to be hooked up right. I don't have a circ pump or thermostat ,just a crossover and added new exhaust etc,could it be air pockets?Seems intermittent.

Sometimes the tips on the impellor can get small pieces nibbled off which can not be noticed unless you pull the impellor out of the housing. This happened to me. The symptoms sound the same as mine. Drove me crazy for a month.

Also make sure that the rubber seal, at the top of the brass tube in the lower unit is good and set properly into the base that it goes into. That one drove me crazy for a while.

well,I found it! Like John B said,but worse. The plastic housing was gaulled badly and the impeller had big groves worn in it. I have an impeller but need the housing. Ebay has one for 68 with imp,guess I'll buy it,,,Glad I took it apart,would never have believed it.Thanks

I was going to say check for grooves in the housing, they let a lot of water and preasure past. Good job. Use vasaline to install.