Water pump impeller blades

[insite]

Extra engine.

[insite]

you know, i'm looking at these pictures now & something concerns me. when i spoke earlier about coolant flow bing from the engine to the radiator over the thermostat, it was a general comment; cars are engineered that way for a reason. FYI, a centrifugal pump like the boxster's water pump is designed to suck from the center and blow to the edge, so we can deduce direction this way.

looking at our photos, two things strike me as very odd:

1. the thermostat opens to the low pressure side of the water pump. this means that the pump IS sucking water from radiators across the thermostat. this is not common, and strikes me as incredibly stupid. the cooler water from the radiators would cause the thermostat to start to close again almost immediately. the temp the thermostat is 'seeing' is the cooler radiator water combined with some engine recirculated water. this would imply our 190deg thermostat is actually running the engine at MUCH higher temperatures.....by design. essentially, the thermostat would try to achieve a 190deg exit temp from the radiators. hmm.....

2. the second thing is that our thermostat looks like it may be two thermostats in one. it looks like the bottom of the thermostat covers 'D' in the photo & like a second spring/actuator rod opens this second 'stopper'. my GUESS is that this is an attempt to heat up the heater core / passenger cabin before any other concern. i want to drop one into a water bath to see if this is the case.....

raby's point w/ the low temp thermostat is that when they measure engine temp at multiple points on test motors, they see some areas that get really hot WAY before the OEM thermostat starts to open. this design could be a reason why.

anyone else have thoughts on this?

[JFP in PA]

[Topless]

insite,
I think we are missing something here. I need to look at a complete cooling system diagram to get clear on this. I can hardly believe Porsche set it up so coolant water flows from rads to t-stat to motor. It makes no sense.

[insite]

JFP - good diagram; pretty much sums it up.

Topless - I poked around my spare motor today; the water pump DEFINITELY pulls water past the thermostat. The TStat is downstream from the radiator. Seems a bit of a mistake to me.

[insite]

Checked a vette lt1 diagram and it's the same; thermostat downstream of radiator. WTF? Makes no sense to me. What am I missing?

[insite]

Btw frodo, this doesnt change the direction you want to flush the motor at the pump

[Frodo]

Originally Posted by insite

Extra engine.

Nice to have a spare, eh?

Originally Posted by insite

Btw frodo, this doesnt change the direction you want to flush the motor at the pump

OK, I was half way through typing that question when I realized you had already anticipated it and responded (with the answer I expected!)

The other question I had was one of PRESSURE. I've been told (thank you, JFP) that too high a pressure, including that produced by a garden hose, could be a problem when flushing, especially with the radiator, heater core and oil cooler. Per suggestions from more than one source, I plan to back flush the engine and the rest of the system separately. With regard to the engine flush, the first two (radiator, heater core) wouldn't be involved I guess (though I'm wondering if I'd need to clamp off the other big hose---the one not shown in my pics, the one NOT going through the t'stat---to be sure that's the case.) That may be all moot, though, since back flushing the engine (ie through D) will still include the oil cooler.

The conclusion would then have to be that, if too high a pressure can be a problem, that would still be true regardless of whether you're doing the engine circuit or the rest of the system (radiators, etc). True?

For those who have done back flushes, have you worried about (or even known about) any potential problems with too much pressure? If so, how have you worked it so as to not exceed a "safe" pressure? If you didn't worry about it, have you had any problems?

I ask, because I had considered (considered!) using this:



It's a plumbing tool, for unplugging stuck drains. The attractive feature is that, when attached to a hose and water turned on, the black rubber part expands, filling whatever hole it's in. It creates a pretty tight seal. Then the water that flows actually pulses somewhat (maybe helping to stir up missing impeller blade pieces!). Without being able to measure the pressure it creates, I'm a little hesitant to use it. OTOH, unless I can incorporate some sort of pressure gauge into the system, I'm not really sure how to monitor the pressure anyway (with or without the plumber's tool).

Thoughts?

[Paul]

Here's some pictures of the original pump in a 2000 2.7 with 40K miles. Looks pretty good, but I'm replacing as many problem parts as possible.

This indicates that the pump is original since the gasket had to be cut:



All blades intact and no slop in the bushing:

[Topless]

Ok I gave this some thought and I think I understand why the motor is on the pressure side of the pump. It creates a higher pressure zone when picking up heat in the water passages which raises the boiling point. A few psi makes a pretty big difference (Boyle's law). Now the T-stat simply acts like an automated valve. When it opens coolant is sent to the radiators and when closed coolant returns to the water pump for recirculation through the motor.

Frodo,
I like the water jet idea a lot. The pulsing action should help to free anything that got lodged internally. As to pressure, you can get a drip system pressure regulator that will bring your hose pressure down to 15-30psi at any garden center or hardware store. Also use a ball valve so you can control the water flow and ramp it up slowly. I might put a catch screen at the other end and take inventory of everything that comes out. You can count the pieces and see if you got everything.

[stateofidleness]

Is the water pump able to be swapped without lowering the engine at all?

Is it a one-man job? I always get pretty paranoid when attempting a job that requires the car to be on jack stands.

[blue2000s]

Originally Posted by stateofidleness

Is the water pump able to be swapped without lowering the engine at all?

I did mine yesterday with the rear wheels on ramps, no engine lowering. But the back of the car does need to be up in the air.

I didn't need to remove the thermostat hose either. The pump can come out through the bulkhead access door. I also didn't replace all my coolant, it was only a couple of years old so I just replaced the 2 gallons that drained from the pump.

Originally Posted by stateofidleness

Is it a one-man job? I always get pretty paranoid when attempting a job that requires the car to be on jack stands.

There are alot of jobs that require the car to be on jack stands. Limiting yourself to jobs with the wheels on keeps you from doing alot of fairly easy jobs.

[stateofidleness]

I know... working on acquiring a lift, but the shipping/hauling home aspect is quite a hurdle.

I had an "experience" once when lowering my Blazer way back when... car on jack stands, lowering rear axle, and *SNAP* whole thing lowered on me... scary.

I'm also nervous because the jack stand area is like a donut, but the top of the jackstands is a "claw"... (they need some kind of standard here). where do y'all put the floor jack so as not to take up the jack stand spot?

EDIT: I have had the rear on ramps before and have had been able to "one tire at a time" a few jobs (spark plugs, brake rotors/pads), but thinking of tackling the motor mount / water pump combo as preventative maintenance.

[Frodo]

Originally Posted by Topless

Ok I gave this some thought and I think I understand why the motor is on the pressure side of the pump. It creates a higher pressure zone when picking up heat in the water passages which raises the boiling point. A few psi makes a pretty big difference (Boyle's law). Now the T-stat simply acts like an automated valve. When it opens coolant is sent to the radiators and when closed coolant returns to the water pump for recirculation through the motor.

Still seems weird to me. As Insite points out, why would you want a system where, when the water (coolant) circulating around the engine gets hot enough to need the radiator action for removing some heat, you then start pulling relatively cool water from the radiator part of the system across the t'stat, presumably causing it to close back down? Sorta defies logic.

Originally Posted by Topless

Frodo,
I like the water jet idea a lot. The pulsing action should help to free anything that got lodged internally. As to pressure, you can get a drip system pressure regulator that will bring your hose pressure down to 15-30psi at any garden center or hardware store. Also use a ball valve so you can control the water flow and ramp it up slowly. I might put a catch screen at the other end and take inventory of everything that comes out. You can count the pieces and see if you got everything.

Not familiar with your 'drip system pressure regulator' but sounds like it might be worth looking into. As to the valve, you don't think that could be controlled well enough with an assistant slowly opening the spigot the hose is attached to? I'm no engineer---probably already abundantly clear---so I don't really know much about characteristics of the various different kinds of valves.

I had already planned on doing the catch screen thing.


Quote:

Is the water pump able to be swapped without lowering the engine at all?

Originally Posted by stateofidleness.

I agree with blue, it is doable as a job on its own. Since I was doing the motor mounts at the same time, I think I did raise/lower the engine some when trying to get to the bolts holding the water pump in place. Made it a little easier, but I'm pretty sure I could have done it without doing that. I also worked from inside the car through the access panel behind the seats to get the top bolts. How old is your motor mount? As Pedro (and others) have pointed out, these jobs kind of go hand-in-hand. Doing one kinda makes the other easier.



QUOTE:

Is it a one-man job? I always get pretty paranoid when attempting a job that requires the car to be on jack stands.

Originally Posted by stateofidleness.

Geez, I know what you mean. I was helping my kid replace a fuel pump in a 1999 Mercury Marquis (his gf's car---I call it 'the starship'), and we had to remove the fuel tank (since that's where the fuel pump lives). I was nervous as hell gettin' underneath this beast of a car sitting on jack stands. I've got lots of lumber layin' around that I'll stack up under strategic support points in case something gives way. If you're removing a wheel, you can also slide that underneath the car. The trick is to make it safe without getting so much stuff under there that you have limited access to get you under there.

As far as the 'one man job' question: I've done everything (so far) by myself.


QUOTE:

I'm also nervous because the jack stand area is like a donut, but the top of the jackstands is a "claw"... (they need some kind of standard here). where do y'all put the floor jack so as not to take up the jack stand spot?

Originally Posted by stateofidleness

Do a Search on "jack stands"---there's all kinds of recommendations and good advice out there. This is how I do mine...

Jacking the Boxster

...but there's lots of other techniques that can be used. With my system, BTW, note that I don't get under the car with just the jack/4x4 holding it up. One, because there's a small chance the hunk of 4x4 could suddenly crack and, two, I just don't trust a jack that much. I think others would agree with that.

[insite]

topless -

you're definitely correct that the pumps are designed to apply pressure into the engine; this is normal. it's still possible (and usual) to do this, but to put the thermostat on the other side of the engine at the large outlet. this way, pressure is into the engine, but the thermostat is placed in hot flow rather than cool flow. bottom line: the thermostat is usually (i thought ALWAYS) at the coolant EXIT of the engine, not the entrance.

Originally Posted by Topless

Ok I gave this some thought and I think I understand why the motor is on the pressure side of the pump. It creates a higher pressure zone when picking up heat in the water passages which raises the boiling point. A few psi makes a pretty big difference (Boyle's law). Now the T-stat simply acts like an automated valve. When it opens coolant is sent to the radiators and when closed coolant returns to the water pump for recirculation through the motor.

[insite]

frodo -

don't worry about pressure unless you have an actual means of pressurizing your system. the pressure in your engine can't get above the water pressure from your hose, which is not very high.

you asked what COULD happen if the pressure got too high. the answer is that you would pop a freeze plug out of the water jacket. these are pressure relief plugs designed to pop out if the coolant/water freezes & starts to expand.

[jaykay]

What is the nature of the rear motor mounts? Can and damage occur by lowering the engine at the front? How much rotation is allowable so as not to damage the read mounts if any at all. Its hard to see in there without a hoist