I have fitted a CSR model 905 electric water pump to my 351 clevo, in order to line the two out put legs of the pump up with the left and right block entry holes, I had to blank off the third hole just below the thermostat, which appears to be a recirculation bypass for when the thermo is closed. I now have a massive overheat problem in the right hand side(cylinders 1 to 4) I had a heater out-take hooked directly into the pump and returning to its normal spot just by the thermostat, I thought that this was stealing the pressure for the right side, and blocked its flow, to no avail. I have a thermo with 3 off 5mm drilled holes to aid flow when closed. After about 5 mins at 2000 rpm, the temp will be up to half, the twin 12" thermo fans are running flat out, but the temp will slowly rise if the car remains stationaru,right up to red. Running out on the highway, at 100 kph, the temp stays at halfway, but if I stop to check under the bonnet, the right bank headers are glowing dull red. The pump fows at 30 gph which I thought would be ample pressure to force flow thru the block. Has anyone else fitted one of these pumps successfully? And can anyone tell me where I can find a head water flow diagram for the clevo, so I can understand more about what may be happenning? Yesterday I removed the rh head to check the gasket was corect, which it was. Today I will try removing the thermo, but dont see that being a solution as the lh side appears to be fine. Any help appreciated, thanks.

okay, after todays work on the prob, I'm coming to the conclusion that what I assumed was just a pressure bypass, and blocked off, might actuually be the return flow for the rh head. I must be getting some flow in there, cos I took it for a two hour run today and the temp stayed at half, but maybe its a reduced return flow, anyone got any ideas?

 

 

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Yes that hole is indeed a coolant bypass. So while the thermostat is closed it blocks the orifice(the brass plate below the thermostat) hole and the coolant circulates around the engine through the water pump. By blocking that off you gave it nowhere to go which would certainly cause hot spots. Make sure you use a thermostat with the large orifice block off pin(like a Tridon high flow type). If you don't this can cause cooling problems all on it's own because the coolant will bypass and result in coolant circulating only in the pump and not through the radiator.

Pete.

thanks pete, that was my original guess, and the reason I put the holes in the thermostat to try and encoure flow even when the thermo was closed. I took the pump off again today, to make sure that I had the most unobstructed flow on both sides that was possible, I have just finished enlarging the backing plate holes,right out to the o-ring limits, and intended to replace the ordinary thermostat with a hi flow one tomorrow. I also checked the pump flow on the bench, its aroud 120+ litres per minute, no worries on low flow there. I wondered if I should tap a hose into the top hole that I covered and take it down to the inlet side of the pump. Might try that if the hi flow thermo doesn't do anything. Any thoughts on that?

Yes it is essential for proper cooling that the bypass works. Making sure the orifice pin on the thermostat fills the hole properly is also very important. It will ensure no hot spots occur because the coolant will actually flow out to the radiator too fast....it must have a chance to transfer heat into the coolant.
Ive seen more than a few clevelands get hot because they just used any old thermostat. One or two were blamed on a .060" overbore before they fitted the right thermostat.

Pete.