Water Pump Housing Shims - When are they needed?
 

It's been established S4 water pump housings use shims where the gasket isn't present and S5 housings don't. I've confirmed this in the parts fiches and I also noted that the S4 shims have two different part numbers depending the the VIN. What I don't know is what is different between the S4 and S5 that necessitates this. Is it the front irons or the water pump housings that are different?

I ask because I have a S4 front iron and a S5 water pump assembly and I'm trying to figure out if the shims are needed or not. If someone knows, great! If not, I'll try to take some measurements tonight and report back for future reference.

Water pump.

I measured the thickness of water pump housing to front iron gasket and the shims supplied by Mazdatrix (1757-15-106). Both came out to approximately .020 in. thick so it was looking good for using the shims. However, when I test-fit everything together I was getting a small gap between the water pump housing and the front iron with the shims installed. I was easily able to fit a .005 in. feeler gage in there and a .010 in. gage fit with some effort. For my application my conclusion is the shims should not be used. My hypothesis is that is the difference is in the water pump housing not the front iron, but I'd need to test all the other possible combinations to confirm.

Did you measure with or without the housing gasket?

The gaps were checked with everything installed and torqued "reasonably tight." Without the shims I had complete contact all the way around at the housing-to-iron interface. Without the shims a I did have a small gap at their location (<.005 in.) but I think this would disappear when the housing was properly torqued down.

Mazda does list another P/N for the shim (there's a VIN split for the S4) and perhaps it's a thinner design. I may order those to check in the future since I won't be starting the engine for some time and it's pretty easy to install them.

To elaborate on this I checked for clearance again after I'd torqued down the water pump bolts and the nuts on the three of the five studs that go through the housing gasket. Without any torque on the remaining nuts I couldn't fit a .002 in. feeler gage between the water pump housing and front iron at the other locations. I'm sticking with my conclusion that I don't need the shims in my application.