has anyone ever had this happen?
a water pump seemingly unable to move ANY water?
L-98 new pump.

Sometimes I can start up, look in the rad filler hole and the water is not moving any..nada, nothing. Zero motion of any kind. Rev the engine..nothing. as if the pump were not turning. Not sucking down, nothing.

After a few minutes it will suddenly start flowing water thru the core as it should. lots of water.

This is NOT a thermostat issue. I have observed this with and without a stat installed.

Its like the impeller is not turning but the pulley IS.

Can the impeller spin on the shaft?

I do not know how they are attached, so I am not sure. This is strange...it did this again yesterday. Temps shot up to 240 in minutes. Hardly any pressure in the system and took cap off to see the water sitting still. Placed cap on and attempted to drive home. After a few minutes the temp started to fall rapidly to normal...190ish where the 180 stat would keep it normally.
I've never seen a pump start/stop before...is this even possible?
Regardless, I think I';m replacing this pump. Its lifetime warranty.
I just want to be sure there is nothing else going on.

 

Sounds like you have an air pocket. It's really difficult to get all the air out sometimes because the radiator is so low.

 

Try belching it good first but yes impellers can break loose pretty rare though.

 

I think the impeller is pressed on. I don't think they are pinned.
Sounds like you need to remove/exam/repair/replace the thing.

 

I've seen water pump impellers that literally rusted into nothing.

 

Yeah, but they probably don't unrust and start pushing coolant.

 

In my fairly long life I have seen 2 cars with waterpump problems where the impeller would spin on the shaft.. So yes it does happen, but not to often..Sounds like it's slipping on the shaft when cold, after it warms up it expands, then grabs hold enough to push water....WW

 

Thats kinda what I was thinking. Its less than 1 yr old...been fine until recently when it suddenly overheated for no good reason. During my investigation I discovered the lack of water action with the cap off...

1st thought was stuck stat, so it was removed and same thing happened. temps shot up,. boiling in the block, then it would suddenly start moving water and everything would quickly return to normal. Yesterday it did this, and lost 1/2 gal of water out the expansion vent, not alot but it did boil off. But, once it moved water again the temps went down to normal. Its on plain water until I figure this out...

Air pocket is HIGHLY unlikely because this engine has a vent/flush valve installed in the heater line that runs directly to the intake manifold right next to the stat housing.. I have a water hose adaptor on that valve so I can connect my hose, power flush the system AND fill to 100% since I am adding behind the stat and filling the rad thru the lower (suction) hose. This also serves as a vent to bleed off pressure before opening the cap.

Today...no problem. I ran 1/2 tank of gas thru the thing and nothing. 80* ambient, ran a/c trying to make it overheat and it would not budge past 200 even sitting at extended idle with a/c on.

I have to admit that I do not know or remember how impellers are secured to the shaft. This is the HD version with a "performance" impeller, which means its t he stamped POS with a band around the whole thing to catch more water to fling it a bit more efficiently. Not as good as a cast unit, but better than a plain stamped impeller.

The only other time that I have witnessed a running engine that did not move ANY water....was when I ran this engine without the belt to test for combustion leaks into the cooling system. Now as it did then, a running engine had zero effect on the water. Pulley spinning, rev to 3000....the water does not move any at all..no sucking down...like the engine was off. Its weird.

It does move water very well when it moves...This afternoon I had the passenger side up on the floor jack spraying off the underside so we can do some work tomorrow, and took the cap off while it was in the air. It looked low in the filler so I added water to see how much was missing. About 1 cup...maybe. And that was only because it was tilted so the filler was the high point in the system. No loss of coolant today...but there was no extreme temp either.

Guess I'll get a new pump and plan on pulling the old new one out real soon. Its gonna get dissected so I can be comfortable that the problem has been solved. I don;t sleep well until I KNOW its fixed!

Thanks for the input,. I've never seen an impeller spin on the shaft but I figure its possible. if you guys HAVE seen such a strange thing...then I'm good with that diagnosis !

 

you're not going to see movement in the radiator until the thermostat opens. You've got air problems.
Don't believe it's the pump

 

Check your bottom radiator hose has the spring inside, it prevents the hose collapsing and blocking flow. So check your bottom radiator hose is not collapsing causing the blockage, when it heats up the pressure will prevent this. That seems to be what you are describing.

 

had an issue similar to what you posted with teh spring.
What fixed it was the right radiator cap.
Car (a body) called for a vented cap, had a non vented so would be fine until you hit cruise speeds and held it then it would collapse and heat up. Bring back down to idle, woosh, flow.
With the proper cap you dont need a spring but wont hurt.

Almost NO hoses these days come with them.

 

Impossible. Please re-read my previous postings..

re:
tested with NO STAT installed. same symptoms.

system is filled under pressure via hose coupling that fills thru the intake, not the radiator. vented out thru the radiator.

 

yep...

dug into that theory too. It does have a spring/coil inside and the guards/shape shields on the outside to fit it across the brace without kinking. Even IF it were a hose collapsing...there would be SOME motion in the radiator. This was perfectly still. Motionless. Like the car was shut off and stone cold. Not even a bubble.

The ONLY other time I have seen that is when I took the belt off and ran it. I have worked with stuck stats...water still sucks down in the radiator because the pump is pulling it. It cannot go anywhere but it tries. There is reaction in the liquid to the motion in the pump housing.
In this case, there is absolutely NO movement of ANY kind. Exactly like it was off...belt off, engine not running. There is a slight vibration in the water from the radiator vibrating with the engine rpm. Ripple effect.
Then after a few minutes and temps hitting 240..the water will start gushing thru the veins and flowing like a river thru the rad core.

Again,. the thermostat is laying in a pan on the stove. The stat is reinstalled. The problem is unrelated to the stat. Happens one day, not the next.

 

https://www.elance.com/samples/autom...arts/39100199/

 

looks pressed at the pulley end and impeller...that makes the spinning impeller theory all that more believable...I think.

 

Below is part of an article about failed water pumps, just to show it can happen..I did a search under this title..."Can a waterpump impeller slip on the shaft?"...There are many articles about this subject.Check it out......WW

It also says the way they install an impeller on a shaft, is to heat the impeller and freeze the shaft before pressing the 2 parts together....

Service warning: The water pump is failing
When the bearing goes bad, the coolant will leak out through the worn out bearing and will drip down the front of the engine. In some cases the impeller will slip on the shaft and the water pump will no longer pump, even though the bearing does not leak. When this happens the engine will overheat. Change the thermostat to rule out a broken thermostat if the engine is overheating, then suspect the water pump. Of course, you must have coolant in the engine, so check the radiator for full when the engine is cold.

Here is another example that it can happen:
Impeller slippage: Another water pump failure, is the impeller slipping on the water pump shaft. Since the impeller and shaft is a press-fit assembly, slippage occurs most frequently on remanufactured water pumps. In other cases where a plastic impeller is used, the plastic material can degrade through sustained heat and age. In any case, slippage can be intermittent in nature and can depend greatly upon the temperature and speed of the engine.

 

Interesting WW7...

In all my yrs I have had many pumps fail, but always seals or bearings. I've had bearings so sloppy that the shaft would flop around 1/4" but did not leak !

Looking back, I cannot recall ever seeing a failed pump that simply did not pump anymore...

It'll be next week or the following weekend but its coming out. I can;t wait to take this thing apart and see WTH...

I have to "prove" any repair or failure so I'm satisfied that its fixed right and no longer a threat...so this will be examined closely. When diagnosing, running eng and NO water movement, I could squeeze the top hose and make water move. I could apply pressure to the vent/flush line and water moved so I am certain there was no air pocket. I even removed the stat and boiled it to make sure it worked right..and ran the car without for a couple days and the same thing did happen again.

theres a first for everything. Wish I'd read about it somewhere though...

 

I hope you figure it out soon, nothing worse then nice weather coming, and your car not working...Im not saying that the impeller slipping is definitely your problem, Im just pointing out that it's a possible cause and has been known to happen before. It looks like you have eliminated most of the normal things that can cause your problem,so maybe it's time to look at the not so normal causes....Good luck ...WW

 

Do you get any heat out of the heater?
Remove one of the heater hoses, start the engine, it should pour out fast, if not the pump impellar isn't working.

 

Thanks,

yessir, I've gone step by step disproving the usual things. Mostly in disbelief at what I was seeing...a new pump that didn';t pump.
Like I said earlier, its been fine for 6-8 months..then suddenly one day recently the temps shot straight up to 240 or even 250 for a few seconds. I opened the hood waiting tos ee something...but the rad was cold, hoses not under pressure...just a hot block.
The only reason I got suspecious of the impeller was because the FSM test for head gaskets is to take the belt off and start up. The water should remain still. IF there is ANY movement, bubbles or ANY action in the water...ita a bad head gasket because the pump is NOT turning. The belt is off..so........
Knowing what that looks like , that was the 1st thing that came to mind when I saw no movement but the pulley was spinning as usual.

Unless there is a rag or something floating around in the cooling system that blocks the suction...it almost HAS to be a defective impeller.

Odd to say the least.
I'll get to the bottom of the mystery.

Post the results so someone else might benefit and move on to the next exciting chapter of
"Corvette ownership on a budget"

Thank you to everyone that offered a theory or possible solution. Even if it had been tried, hearing it again often sparks new thought. In my old head thats always welcome.