When to Use oem pump impeller？

I want to replace the impeller and o-rings/gaskets on my Merc 170 Alpha I. I plan to get the waterpump kit which has impeller, gaskets, o-rings, and housing (top only), etc. The price difference between OEM (about $66 at GLM Marine) and aftermarket (about $20 at eBasic Power) is quite large.

I expect I'd have to replace other parts in the future, so I'd like to know what I should do in general. Does anyone have an opinion about the quality of aftermarket replacement parts. Is it common practice to use aftermarket parts or are they not worth the dollar savings? Thanks. Re: Replacing impeller... OEM or aftermarket?

Many of the parts you get from basic power are GLM parts.Glm,aquapower,sierra are all good parts.As a matter of fact some of the impellers are exactly the same including the markings.When you get into more serious parts like manifolds,then there is a difference.Charlie Re: Replacing impeller... OEM or aftermarket?

I have found that the impellers from Sierra, and other after-market kits are made from a less durable rubber than the Merc kits.

Usually after one season a sierra impeller has taken a bad set. That is it doesn't spring back out to its origional shape when removed from the housing. This "set" decreases the efficiency of the pump, since it is the springing out of the blades that helps pull water in to the pump. Re: Replacing impeller... OEM or aftermarket?

Think of the money you're saving by doing it yourself. If you're going to go through the effort, why not spend the money and get the real parts? Do you really want to do this every year instead of every other year, or worse, do you want to overheat and damage your engine?

By the way, you should replace the water pump base while you're in there. It has two shaft seals in it that wear out. It costs something like 20 bucks, so to do all that work and leave the old one in there is crazy...

Get a friend to help hold the prop and keep it in gear while you put the gear housing back on.

Good luck and have fun with it.

Steve

The old BMW water pumps had orange or black plastic impellers that were prone to breaking. The newer BMW water pumps have a fiber-resin composite impeller that looks like black plastic, but is much less prone to breaking; however, the stigma of the "plastic impeller" has persisted. Many aftermarket water pumps (such as Graf, I think) have metal impellers.

Both will move the water adequately. Both (composite and metal) will last a while, unless abused or dropped during shipping/installation.

Anecdotal evidence suggests that the bearings in the OEM pumps are better than the bearings in the aftermarket pumps, but I don't think there is real research or empirical evidence to support this. Now that the impellers don't break like they used to, the bearings are the new weak point.

I personally went with an OEM pump with composite impeller.

There's also the Stewart high-performance pump, but that's off in a category by itself, and is several times more expensive than the usual OEM or aftermarket pumps.

Theroetically, the metal impeller will wear out the bearing faster just because it's heavier and it will take more power to spin it.
Also a metal impeller is more prone to erosion than composite. Some composite impellers had a composite shaft and this would end up failing where the shaft meets the body of the impeller. Most I've seen lately have a metal shaft eliminating this problem.
In the real world, I don't think it makes that much difference

+1 to nathancarter covering this pretty well

Unless you are going to be racing / tracking the car, there's no need to go for a water pump with a metal impeller. From what I know, the water pump's impeller is very close to the number one cylinder bore. And, IF the bearing begins to get loose, you could be in a whole new mess with metal spinning around there. However, most folks who are the type to install water pumps with metal impellers are the type that will do preventative, as opposed to reactive, maintenance. As such, potential bearing issues may be moot.

My understanding is that the metal impellers can cause impurities in the coolant as the impellers break down over time. That results in an increased chance of electrolysis which is bad for motors, especially ones with aluminum parts like an e46's. Electrolysis is where there is an actual electric current running through your coolant. Apparently it can lead to leaks as the metal parts in the motor break down.

IMO, this really just means that if you go with a metal impeller, then you'd be wise to stick to the recommended change intervals with regard to yer coolant.

When I did mine, I went with the metal impeller b/c I hadn't heard that the plastic ones weren't plastic anymore.

Just pulled out the water pump in my ride today... its metal impeller, 150k miles and the first noise was heard... This water pump/fan clutch however was the WORST repair I have ever had to do on this car... I spent all day and I am still not finished. I'll post pics and information in another thread... It was quite an adventure.

Not quite knowing what I was doing, not wanting to go to OEM and trying to get it at a decent price, I ended up with a fiber impeller. Of interest is that I have this urge to follow a trusted path, if this is at all possible. I first looked for supercharger oil which turns out to be a GM part, as OEM is not/never was available. I have the oil. With 90k on the odometer and one of those noises, taps - whatever - coming from under the hood, i figured that I should find out what's up. I purchase the car with 67k - so I don't know its history. I took it apart and found two noises - the idler pulley and the water pump. I settled on A C D e l c o parts for the water pump, Idler pulley, belt tensioner & belt. I can't have an opinion about the supercharger until I have resembled and run up the engine. MINI Cooper S R53 engine W11 production date 09/ - acquired in July - 67k - at 90k.