Timing belt/water pump replacement

[Rick Rae]

Originally Posted by Bill in Houston

Yeah, it would use electricity from the alternator, but it would pump the right amount of water, instead of 6 times what you really need, so it would save that way. It's the same idea as the electric cooling fans, really. It would run at "low" speed most of the time, and kick up to "high" if it needed to.

I agree, it should help. On the other hand:

1) A mechanical pump is a direct mechanical-to-mechanical drive. With an electric pump, you're converting from mechanical to electrical (via the alternator/battery) and then from electrical back to mechanical (via the electric water pump). The losses in both conversions will limit the possible gain.

2) I imagine most hypermilers run lower revs in general, so the gains from "as needed' pumping may be less for us than for the typical lead-foot.

Plus I read someone's test where they completely removed the drive belt(s) -- taking out the alternator, A/C compressor, etc. (not sure if the water pump was on that list) -- and only reclaimed about 3HP.

I have no doubt that an electric water pump would help. How much it would help is an interesting question, though.

On the third hand you're talking exactly the same parameters for electric fans versus mechanical drive, and haven't we determined that offers a usable improvement? I would think a water pump conversion would be similar.

Unrelated to FE but still an issue: If the water pump is driven by the timing belt, then if one switched to an electric pump, wouldn't they need either an idler to take the place of the mechanical pump, or a different (shorter) timing belt (if such a beast even exists)?

I'm not trying to be argumentative here -- just tossing in some reasons why the switch to an electric water pump may not offer the level of benefit we might like.

Now, someone show me I'm wrong and we're actually talking about a 10%-15% gain potential here so I can get one ordered.

Rick

[Bill in Houston]

Originally Posted by Rick Rae

Unrelated to FE but still an issue: If the water pump is driven by the timing belt, then if one switched to an electric pump, wouldn't they need either an idler to take the place of the mechanical pump, or a different (shorter) timing belt (if such a beast even exists)?

I'm not trying to be argumentative here -- just tossing in some reasons why the switch to an electric water pump may not offer the level of benefit we might like.

Now, someone show me I'm wrong and we're actually talking about a 10%-15% gain potential here so I can get one ordered.

Yeah, no, you're not being argumentative. I'm not sure how much hp a car's water pump draws. One hp? A 1-hp pump will move a ton of water. But, then again, if you can reduce your power demand by 1 hp, you would bump your mileage at least 5%.

With it being under the timing belt, I think it goes beyond the level of complexity that I would want to attempt.

If you did go to electric, you could do other cool stuff like reverse the flow so that "cool" water goes to the head first. Oooo, and have a Prius thermos thingy...

Really, I was just thinking out loud and hoping to give you something to go on so that YOU could generate the actual good ideas. :-)

[Rick Rae]

Originally Posted by Bill in Houston

Really, I was just thinking out loud and hoping to give you something to go on so that YOU could generate the actual good ideas. :-)

Hahaha... way bad move... trust me on this one...

I'm not sure how much hp a car's water pump draws...

Well, even the small incremental stuff adds up. I just made my DRLs switchable even though that's at best a tenth of a horsepower. I posted the question because you never know when someone's going to say something like, "Yeah, have them put on a DRZ52A pump from a Mk2 Jetta instead of the Mk3 Golf version, it's the same mount and will cool things okay but it's 20% smaller and puts less load on the engine..."

With it being under the timing belt, I think it goes beyond the level of complexity that I would want to attempt.

And me as well, I'm not worth much under the hood. I've swapped batteries, replaced broken heater hoses, exchanged starter solenoids, stuff like that. Anything of significance I leave to people who know what they're doing. In fact I'm letting the dealer do this one (even though that will mean big bucks ).

I do want to dive in and start tinkering once the VW is no longer my daily driver or vital to my making a living. I love this little car and it'd be fun to see just how much FE I can wring out of it. But for now I'm limiting it to air dams (coming next), fender skirts (I hope), switchable DRLs, hunting for the control lines so I can turn the cruise control into a throttle lock... things that can't get me into too much trouble.

Oooo, and have a Prius thermos thingy...

Actually, with as much stop-and-go as I do during a business day, that might pay off in the Winter. Hmm...

Rick