Mrmerlin

hopefully you didnt get a Chinese WP.
If you follow the above instructions and the car runs to hot after 5 mins of idling ,
then its a pretty sure bet the WP isnt working,
Roger has a great deal on new Lasos

DougM

Pulled the thermostat and it was not in backwards. Also dropped it in boiling water and it expands.
Buttoned it back up and refilled the system. Ran the car for 10 minutes with the cap off and then put it back on and drove around the neighborhood. All seemed to stay well with the gauge at about 1/2 way. Suddenly, as I was turning into my driveway, the car would not hold idle and died. Turned the key off and it began to boil over. Turned the ignition on to get the gauges and now the needle was at the red mark. I let the car cool down for a while and it fired right up so I could get it back into the garage on the lift.
Thinking about it, a similar episode did happen yesterday. Right when it was about to boil over, the car lost power and died and all the idiot lights came on. After cooling down, it fired right up???
I figured that it was coincidence and the battery was dying and because I had turned the car on and off many times checking to make sure everything was good.

ROG100

Just for information the three main US based European parts wholesalers do not sell OEM pumps for the 928. They sell rebuilds or Laso new.
How much where you charged for the WP? If it was $100 to $150 it would more than likely be a rebuild. If you paid circa $300 more than likly a Laso new WP.
If you paid $400 plus you either got ripped or it was a Porsche rebuilt or new WP.

I hope it is not your WP but sounds like it is.

M. Requin

Just guessing here, but it sounds like the impeller, when hot, may be suddenly coming into contact with the crankcase and freezing causing the sudden overheat. Cooling, it clearance returns and coolant flows. That is just a WAG.

DougM

Will take a breather and then dig into it and see how the pump looks.
One thing I noticed is that I am using the existing pressure cap on my expansion tank. Never really thought to replace it. If that is bad, could it cause such high pressure to cause my issues? The fact that it could run without the cap with no problem and then within 5-10 minutes of putting it on the overheating happens? I am not real technical on how the whole cooling system and pressure caps work.

Mrmerlin

Doug you also need to get more info and thats done with an IR gun,
it would be helpful to know what the temps are at the top hose and lower hose ,
also whats the temp of the coolant bottle,

As part of a coolant system refresh, yes you would replace the HCV and short hose as well as the coolant bottle cap and thermostat and seals.
From this info provided i would say you prolly have a bad pump dont let the engine keep running hot you can damage the heads and HGs

DougM

Will try to get an IR gun. Here is what I do know. Can run the car without tank capped and it runs without problems, at least idle in the garage for extended time. Put on the cap and heat and pressure rise. The hotter it gets, the quicker it happens. Fluid in the expansion tank is boiling over at this point and blowing out the overflow. I can hear it boiling and there is a lot of pressure which leads me to believe that the cap is not allowing pressure to release. Lat time it happened, the upper rad hose was hot and the lower hose was not. The radiator itself, was warm, not hot.

khalloudy

My money is on the water pump. The plastic impeller is loose indie the housing and is slipping. Don't ask me how I know... Experience is expensive. Always buy a Porsche original part and sleep well at night and stop chasing gremlins.

Mrmerlin

khalloudy in the case of the water pump the new Laso pumps are the best deal,
they have the updated shaft securing rings that will inhibit the impeller from slipping.
Roger spent a lot of time working with Laso to make this pump work

Bertrand Daoust

Yes, if the upper rad hose is hot and the lower one is cooler than you have a bad pump (or the system is clogged with something).
Let us know what you'll find.
Good luck.

FBIII

Your symptoms sound similar to Rover V8 issues. If it will run w/o the pressure cap you might be leaking combustion gases into the cooling system and the system becomes air bound and overheats. Next time you run it smell the coolant tank and see if it smells of exhaust gas. Also look for small air bubbles collecting in the overflow tank.

Shark Attack

cooling isnt rocket science in this car. The thermostat opens and the pump pumps water through the engine. Something is clogged. Another thing you keep saying is "boil over" why is it boiling over? It would only boil over if it lost pressure. Are you running it what the cap off/ loose where is it boiling over at? it shouldnt boil over unless you take off the cap.

when you fill it how much will it take? when you are filling. do you fill with the car running? can you see coolent flowing through the bottle?

928mac

Hmmm i did not expect this thread to go this far.
you need to take it to a shop and hopefully you do not have a cracked head or something like that.
If it is getting combustion chamber gas in the cooling system, then they can test for it.

danglerb

Lisle 75500 about $32 shipped from various usual sources. (amazon or tooltopia).
Combustion Leak Detector Kit
Combustion Leak Detector Kit

List Price $47.43
Your Price $25.24
Item Number LIS75500
Mfg Lisle
Part No 75500

In stock: Yes
Quickly pinpoints combustion leaks. Checks combustion leaks caused by bad head gaskets, cracked blocks and cracked or warped heads. Indicating fluid changes from blue to yellow when exposed to combustion gases in the radiator. Connect the hose to any vehivle vacuum line. Place tapered end of tool into radiator opening after draining of some coolant. With the engine running, the vehicle's vacuum draws vapors through the indicating fluid for testng
Includes leak detector and testing fluid.

GregBBRD

Did it overheat before it was taken apart?