moalaska

So I did some searching and found some answers but still have questions.

My turbo water pump was not turning on. Pulled the top cap off and it looks like it got hot, the plastic holding brush on one side was warped, and I couldn't spin the shaft.

1) will water flow through the water pump and get to the turbo, if shaft is siezed?

2) will water flow to water pump with siezed shaft be sufficient to cool turbo, with proper cool down period?

3) does turbo water pump flow more water than mechanical pump when powered?

Thanks

​

931guru

1) No
2) No
3) The purpose of the turbo pump is to cool the turbo after shutdown, when coking occurs. Not fixing it will cost you a turbo in the short term.

Thom

The main water pump pulls coolant from the coolant tank through the turbo as soon as the small thermostat in the plastic elbow on the water pump opens. What the auxiliary turbo pump does is to turn on either when the engine is shut down or when coolant temp in the turbo reaches the rating of the temp sensor on the coolant pipe out of the turbo housing, whether the engine is running or not.

moalaska

I'll bypass it then for now until I recieve a new one. I only took the car around the block a couple times since installing my rebuilt turbo, I didn't even drive it that hard so hopefully nothing got cooked.

moalaska

What is the direction of coolant flow? Through turbo, through electric pump, then to expansion tank? Or other way around?

PF

The turbo is also oilcooled so it is unlikely that you have damaged anything. The 931 and 930 Only had oilcooled turbos and because of it shorter turbo life that was later adressed on the 951 with the pump.
It should turn on as previuosly stated but many only work after ignition shut down for 30 secs and not (as it should) also when temp rises after shutdown. I have never worked out why that is despite having that issue on several 951:s
I made a fix with a rear wiper switch that grounds the turbo aux pump so I switch that on for awhile after stints on track etc to cool the turbo.
Would however be glad to know if someone knew why they seldom work after shut down and temp rises.

Tom M'Guinn

Just be sure to let the engine cool and idle for a while before shutting down the motor. Turning the heater on for the cool down helps too as it both increases the cooling capacity, and dumps the unheated coolant trapped in the heater core into the system for a little extra jolt of cooling... What you don't want to do is shut the motor off right after boosting heavily, especially with dino oil. If you use synthetic oil, and let the motor idle for 2 or 3 minutes before shut down, you can nurse it along without much risk until you get the new pump.

markl951

The coolant pump runs for 30 seconds regardless of coolant temp on initial shutdown of the engine. The stock coolant pipe switch, when hot connects the wire harness lead to GND. That triggers the electric coolant pump timer relay to run for 30 seconds which typically cools things enough to open the switch. Any heat soak that causes the temperature to rise and the switch to close starts the 30 second timer over again. Rinse, repeat...

When I recently installed my rebuilt turbo, I replaced the coolant pipe temperature switch with what I thought was a lower profile switch. It was a sensor and not a switch so on engine shutdown the pump just ran forever. I was forced to disconnect the wire harness lead. The pump still runs for 30 seconds on shutdown but only once.

I didn't want to remove the intake manifold to deal with it just yet so for now I've modified the 555 timer circuit inside the coolant pump timer relay so it runs for about 90 seconds instead of 30. It still only runs once but for 3 times as long.

moalaska

Ok so does the coolant flow to or from the reservoir?

931guru

With a slight modification to the electrical connection, VW/Audi makes a superior and cheaper turbo coolant pump, part number 078965561

You can use one of these pigtails to make the mod:

moalaska

I I already picked one up from O'Reilly's, it takes a fuel injector connector which I got.

Thom

If the thermostat in the plastic elbow on the WP is closed, coolant will be pulled by the (running) electric pump from the reservoir and flow back into it since the closed thermostat prevents it from being pulled by the WP to the engine. Again, when the small thermostat is open it's the WP which is the main cooling source for the turbo, and it will pull coolant through it from the reservoir whether the electric pump is running or not, the difference being that the flow through the turbo will be higher when the electric pump is running together with the engine.