How do you know if your water pump is working (not leaking) up to it's potential? I have replaced and checked t'stat's for the last time. They are working. New rad. cap. I have ran water through the whole system, it's flowing through the whole system best I can tell. Ran water in and out of every orifice I could. My fan clutch seems fine. I believe my timing is fine. I'm not running lean. My carb is to big (750) according to some. I'm down to either the water pump, the carb, or a vacuum leak/air lock issue. I have checked the heater, and it will burn you out. What's my next step?

 

Vacuum leak. How much vacuum are you pulling anyway?

But check your radiator. How old is it? What's it's condition.

 

Pulling about 15 at idle on vac......I did notice it slipping down slowly to 10, but I was thinking it was just the gauge and my connections. I can unhook, rehook and it's right back at 15.....Holy crap, that may be it.

Radiator doesn't look real old. I would guess may 10 yrs. by looks. It was rodded out 3 or 4 yrs. ago per previous owner.

The water pump looks older than dirt. It's all rusted and look like crap.

 

I thought it was a simple question........

 

i guess you would have to measure the flow..... mostly we replace these because they leak, not because the flow goes down.....i guess you could disconnect a hose like the heater hose and stick it in a bucket and see what kind of flow you get but you would have to some how replenish what is being pumped out....i guess you could take the thermostat out and stick a garden hose in the radiator and then measure the flow .....or just buy a new one.....i would think that you have crude in the block that is blocking the flow, you have checked the thermostat to make sure nothing is stopping the flow through it?

 

You said the previous owner rodded out the radiator.

Just my opinion, Maybe others differ. I don't think radiators should be re-rodded. I think they should be replaced.

Anyhow this message is directed to rerodding. I dont really mean to suggest that replacing your radiator will solve your problem. But replacing the radiator is something to keep in mind.

 

Replace the radiator. Rodding it will never get all the sediment out of it. A while back I had a vehicle that was running hot going down the road. I ran a water hose through everything and there was plenty of flow and water moving through the system as well. I checked everything else like the thermostat, fan, and waterpump. So I decided to get the radiator replaced. I went ahead and took one of the tanks off and then ran a hose through it again and plugged the outlet so I could see how the water was flowing through the rows. The entire center area was clogged but the end rows would flow enough water that when the end tank was on, you would think it was fine. Anyway, after replacing the radiator, I never had any hot issues again.

 

Start the car up with the rad cap off. Once the car is up to temp you can see the water churning. Good Luck

 

How wide is a t'stat suppose to open? I dropped mine in boiling water to check, and it only opened about 1/2 and inch, maybe.

 

it should open fully....how much more could it have opened? i would think 1/2-3/4 is the range.....try running the car with no thermostat and see what happens....perhaps the increased flow will move things around

 

You can do that with a lot of motors, but not sbc's - you'll starve the upper portions of the heads for coolant coverage, especially with a possibly lower flow worn pump. The restriction of the thermostat flanges (yes, when open) acts like a "stop log" to back up the flow and level enough to properly cover the key parts of the water passages in the heads.

You know, to be honest, I've only done it once with a stock sbc setup. I wonder how true this effect still is with aftermarket heads and intake and especially aftermarket water pumps. I don't want to risk warping an aluminum head though to find out.

 

Did you ever get a chance to check the lower hose?

 

HMmmmmmmmmmm................

 

Thanks for the responses! Dirt, I checked the lower hose and I can feel the stiff springs in it. Put a 160 T'stat in today for a few test drives, and also bought some stuff to help flush the radiator. We will see...

 

Vacuum leaks are sneaky little temperature gremlins.

The only time I've ever had a cooling issue with my 383 was when the electric fan relay quit working. Even then sitting there idling in 80 degree weather,with no fan, the temp would only climb to 220.

Until one day while tuning the idle circuit, I hooked up a vacuum guage. Once I had it dialed in, I removed the guage but apparently forgot to hookup the vacuum line I had removed from the carb port.

The temps soared to 250 within minutes. Thankfully I was just sitting in the driveway and I shut it down. When I remembered the vacuum line and reconnected it, I restarted the motor, let it idle for about 10 minutes and the temps came back down to normal. All that cause by an 1/8" hole letting air in where is shouldn't.

I'm convinced that's why my L48 ran hotter cruising on the highway.

 

You don't mention here if your car is over heating. Is it? How hot is it getting? If it is overheating is this at idle, on the hyway? When you flushed the car running water through it did you take the 2 plugs out on the bottom of the engine to let the water out? Sometimes you need to run a wire like a piece of cloths hanger through the hole once you take the plugs out because the holes have gunk in them. I usually keep a garden hose running in the radiator while doing this. Your car requires a 195 stat and really no other for emission purposes. It shouldn't over heat with it. If you are not getting enough flow the propellar in the water pump could be rotted out or shot. I have heard of this happening on cars that didn't have good antifreeze in them. Other then that your radiator might just be your problem. You mention that the former owner rodded out this radiator. What do you mean by rodded. I have been in the automotive parts business now 27 years and never heard the term. Do you mean the radiator was recored or sent out to be cleaned? Does this problem you are having happen in the cold weather as well? Is this a new problem or has it been like this when you purchased the car? Fan clutch although it seems to be good could still be your problem. Is it the original? It could be on its last leg. Replacement Chevy water pumps for this car are still relatively cheap for a new or rebuilt. If you change the pump make sure the parts house doesn't give you a reverse flow pump. They look the same. I think the reverse flow pumps started to be used on small block Chevys in 89'-90'. To look at them you really can't tell the difference and you wouldn't want one of those on your car unless it called for it.

 

Temps are running about 225 at idle in garage. Temp will increase to 230 235 range when running down highway. The reason I know I am getting flow to the block is I still had the t'stat housing off when testing. Water flowed out of the opening where the t'stat goes. Both fans working. It could have been an air lock. I'm going to be carefull when filling to try and not get to much air in the loop.