Timing belt/water pump replacement
 

It's time to have the Cabrio's timing belt and water pump replaced. Just thought I'd ask if I'm missing any opportunities for FE improvement here (e.g. a higher-efficiency pump, change to electric, low friction timing belt :D etc.)

Thanks for any insights,
Rick

I think that changing to electric would help FE. And power, really. Spinning that thing 6000 rpms when you wind 'er out has to take quite a bit of power.

Hey, wait a minute. I don't know how many people know this, but restricting the outlet on a centrifugal pump will generally reduce the amount of power it draws (which I know is counterintuitive). So if one could restrict the water pump outlet, one could reduce the amount of drag the pump causes.

But you would want for it to be controllable in case you REALLY DID pull a 5000 pound trailer 100 mph up a hill on a 110 degree day...

Anyway, something for one of the genuises here to figure out - an easy, adjustable way to restrict the outlet of the water pump...

Someone with experience with pumps come to bat for me here too - centrifugal pumps draw less current or use less power when the outlet is restricted, right? I know someone is going to try to smack me around for suggesting such a thing.

I've heard about the electric water pumps, but have shied away from them for now. Too expensive, not enough testing done for the Jeep applications. Also, on the Jeep.....the water pump sits up against #1 cylinder. water pump grenades = holes in cylinder wall. Don't laugh too hard.....I've seen it done.

I think I would put the pump somewhere away from the block for reasons like that. Since it's electric, I could put it wherever I wanted.

but then you have the electricity to run the pump coming from where? the alternater which is driven by the belt...a replacement pump is usually under $50 while im guessing an electric one is more. have any of you spinned the water pump pulley with the belt off? theres very little rersistance... same with the power steering pump

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.

Find a wrecked new BMW 3 series, I'm pretty sure they have atleast the electric water pump part down, maybe the variable nozzle as well.

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. :D

Rick

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. :-)

Yea, advance that cam!

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

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..."

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 :eek:).

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. ;)

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

Rick

Bill your correct a centrifugal pump requires less energy to spin when its dishcharge is restricted, it also produces more pressure when restricted.

Low flow rates require less energy, high flow rates require more energy. If you look at it from the flow rate perspective it makes perfect sense. More flow = more mass moved = more load.

Controlling the flow rate of a belt driven pump would require another valve and thats not going to be easy to rig. Installing a variable speed electric would be the best way to go with a temperature controller running the pump.