Big Block Water Pump

[Al Tyson]

As you know on previous threads I have been having a problem with boilover. I tried a new thermostat for the hell of it tonight and within 5 minutes it was 240 and ready to go over. When it was cool I took the cap off and started it and water trickled out the core. It never had a fast flow. My question is the water in the radiator gets drawn from the bottom hose through the pump. The output of the pump goes into the manifold. The manifold has an outlet for the heater hose(with the heat control valve) and the return outlet with the thermostat in it. Then how does the water flow in block and back out the return to the radiator so it can be cooled. It seems to me that it almost bypasses the block. Thanks for the patience and info. A couple of local "mechanics" say pull the radiator and install a new one. I would like to nail it down before doing that. I was thinking of taking the 90 degree elbow off of the water pump and put in a clear plastic hose to see the flow. Of course, I would do this cold and stop before it got hot. In that way I would be checking the water pump flow. Good idea?

Al

[Joe L.]

Re: Big Block Water Pump

Al------

The cooling system on a big block is of fundamentally sound design and it does work quite well on most of the millions of these engines that have been built since 1965. And, the coolant does not bypass the block; in fact, that's the first thing that gets cooled.

In big block Chevrolets and most small blocks (except 92-96 Gen II LT-1 and LT-4) the coolant is drawn from the radiator through the lower hose and pumped through the block holes which are behind each of the water pump legs. Then, the coolant circulates through the block cooling jacket, up into the cylinder head cooling passages, and, finally, through the intake manifold crossover passage in front of the manifold. From here it goes through the thermostat housing (impeded, as necessary, by the thermostat to regulate engine temperature) and back to the radiator through the upper hose. Actually, it's a bit more complicated than this, but this is a simplified description.

The "90 degree elbow" that you mention is the coolant bypass. The amount of flow through this would not be very indicative of general flow through the engine and, I would say, would not provide you with useful information relative to possible obstructions in the block, cylinder heads, or radiator. It might provide some information relative to the output of the water pump. However, except for bearing and seal failures, water pumps are fairly reliable and bullet proof. If yours isn't leaking or making significant bearing noise, it's most likely just fine. Even if it is doing one or both of these things, it will usually continue pumping until one or the other fails completely.

[grr]

Re: Big Block Water Pump

Al, Joe's correct with the flow and the water pump infomation he provided you. You have a flow or restriction problem. Didn't you say this was a radiator that was just serviced, and that you tried running w/out a thermostat in a tread last week?? Not sure but someone did.

If it's an old radiator(original)you may need to replace since you have such poor flow. A bad water pump either starts squeeling or leaking before going down like Joe said.

I just had my radiator cleaned/pressure tested as it was leaking but I always had a good flow through it. You have to move that "hot" engine water through radiator so it can carry away the heat created by the engine. No flow only means your sorta like heating water on a stove in a pan, no way to cool it unless you shut down so it boils.

You haven't added any radiator stop leak have you in the past? I'd take the advice of the mechanics as they know good flow when they it. Take the car down and show them, maybe they will see another problem.You don't want to hurt your engine.

One other hint, what was the last thing you worked on in reference to the engines coolant flow probrem? That may be it, I always check the last thing I worked on if it worked before I touched whatever.grr#33570

[motorman]

Re: Big Block Water Pump

have you had the rad flow checked? all good rad shops have a flow checker to test to see if the rad is flowing up to its rating. this is where i would start if you have not done this. the second thing i would try is adding the chemical to the water that changes color if you have combustion gases getting into the water. a trick you can try on your own is to remove the top rad hose,and gooseneck. fill with coolant to the top of the manifold outlet, remove the water pump belt and start the engine to see if any bubbles show up at the water outlet in the intake manifold. if they do you have a head gasket leak.

[Iron Duke NCRS #22045]

Radiator flow is the key!

If the radiator is clogged up from all the junk in Prestone the engine will run hot and/or overheat. One way to check flow (on a BB radiator with a cap on the side tank) is to reduce the coolant level to expose about six tubes. Then start the cold engine and wait for the thermostat to open. When it does, coolant should flow freely out of the tubes. Nobody has been real specific about what these radiator shops are doing. Sure, they all leak test the thing, but that doesn't tell you anything about flow. A good shop can do a qualitative flow test, but the best way to check the radiator is to unsolder a tank and visually inspect the tubes, and if they're clogged do a "rod out" or a recore if necessary. Deposits block flow and also increase the radiators thermal resistance. It's a double whammy. My gut level feel is that a lot of the cooling system problems on BBs are due to clogged up brass radiators.

We know the BBs had little design margin to begin with, and it you reduce the radiators heat exchanger efficiency by even 20 percent or so, it's gonna run hot and keep getting worse.

Duke

[motorman]

Re: Radiator flow is the key!

the shop i deal with has a setup with a large flow meter where they flow the rad and they have a chart with all the rad part# vs flow rate and they compare the flow rate. the race car rads they build they flow them when new and keep a record so they can flow check them later if a problem shows up. race car guys always use stop leak.

[Wild Bill]

Re: Radiator flow is the key!

Checking flow the Iron Duke way, will tell you about water pump flow and the top 6 inches of the radiator. If the radiator is clogged, it usually starts at the bottom and fills up. To check for this , feel the radiator from the front after the therm opens with engine running about 2000 rpm. If the bottom is still cool, center warm and top hot, you have your answer .

Good luck, Wild Bill