"Thar She Blows!"--- Again

[Duke W.]

Re: Thanks To All

Hey Clem, it's heatening to know that ace mechanics can screw up, too.

Duke

[Clem Z.]

Re: Thanks To All

duke i even have one better than that. the time i could not get a small 2 stroke powered water pump to start. it had spark,fuel and compression but would not start and i had it half apart before i found a mud wasp had built a nest in the exhaust plugging it close.

[Joe C.]

Suspect Water Pump

Yes, I put the oil in the rad., and the water in the crankcase, as per the instructions that came with the kit (heh, heh!)--I even tried a baking soda and water mix for propulsion, but that didn't work either!!

Seriously, the fan is correctly installed, and the timing is AOK. Here is a lead to what is possibly wrong. When I squeeze the upper rad hose, engine running, cap removed (to prevent pressurization of the system) it feels like a limp d---. It feels like there is no pressure out of the pump. Now, I don't want to go there yet, because this is a newly "reconditioned" original that I purchased at a well known Corvette parts house. It runs quiet, no leaks, with a tight bearing. The only thing I am thinking is that I will remove/disassemble it and probably find a bad impeller.

Before I get there, I have a couple questions:

1. With the reservoir cap removed, should I see a flow into the tank from the rad return hose (small dia hose into tank just below cap)after the therm opens?? I do not.

2. Shop manual calls for 17 qts, and owners manual calls for 19 qts coolant. When I filled the system (block was completely dry), it only took 16 qts total. Is there a special way to fill the system? I just kept adding to the tank as the engine ran, and level dropped. Finally leveled off at half a tank. Before I pull the pump, I would like to know if it might be air bound, and/or cavitating.

Joe

[G B.]

Rebuilt water pumps

I would not use any commercially rebuilt water pump on a Corvette, regardless of its casting number.

I think the clearance between the impeller and the back cover plate makes a big difference in pump efficiency at low rpm. Many rebuilders apparently disagree, because they seem to pretty much throw the pumps together without much concern for tight clearances. They also don't make certain the pulley mounting surface is perpendicular to the shaft axis. Seal, bearing, and impeller quality in a rebuilt pump is probably based on minimizing cost.

If there isn't one already, I would drill a 1/8" diameter hole in the baseplate of the thermostat to make sure air can bleed from the block while you are filling it.

[Joe L.]

Re: Suspect Water Pump

Joe-----

1) The hose "just below the cap" should be the overflow hose; not the "return hose". This hose should go to atmosphere. The hose which connects the radiator to the supply tank is connected to the radiator at the nipple on the top right and connected to the supply tank at the nipple which is welded into the BODY of the tank. There will not necessarily be a regular flow of coolant through this line;

2) I've always noted that a small block Corvette cooling system does not seem to hold the amount of coolant that the specs call for and I've also noted the inconsistency of specs found in various sources. In any event, 16 quarts should be plenty to obviate a cooling volume deficieny being at the root of your problems. You filled your system in the appropriate manner, too;

3) With the pump operating one cannot expect the pump outlet hose to feel "stiff and firm" like what one would expect on the outlet side of other pumps. Remember, the engine water pump does not generate any significantly high pressure;

3) Personally, I don't see how the water pump could be the source of your problem, but, I suppose, it's worth checking, at this point. If it has a stamped steel type impeller, I suppose that it could have been installed backward. Very unlikely, but theoretically possible. If it has a cast iron impeller, it would be difficult, if not impossible, to install it backward. Otherwise, the only way that I could see the impeller being "bad" would be if it was loose on the shaft.

[Clem Z.]

the clearance is

between the impeller teeth and the machined surface of the pump housing and it should be .015 with a cast iron impeller. never dicked with a stamped impeller pump because the are not efficient at high RPM. could you have gotten a reverse rotation pump by mistake or at least a reverse rotation impeller?

[Joe C.]

Re: Suspect Water Pump

Joe:

Yes, of course I meant the return line from the rad--didn't think I had to state the obvious. Thanks for the heads up on the coolant capacity, as I want to make sure I have all the bases covered, so I can now eliminate the "air pocket/cavitation" scenario. I will target the thermostat next, and then the pump. The rad takes a very long time to get hot after the stat opens- it seems inordinate, which points to a flow problem.
I appreciate everyone's feedback, and I will keep you posted.

Joe

[Joe C.]

Thanks Jerry And Clem

I will go after the thermostat tomorrow, and then I'll look into the pump. I am fairly certain it is a flow problem.

Joe