[beertracker]

The engine is a Pontiac 455. In Jim Hand's book he calls for a .050" gap between the water pump impeller and divider plate. I gapped my water pump impeller with gasket and divider plate to .060" to allow for gasket compression during assembly.

My question is how much do you think the water pump gasket will compress during assembly? Does .010 sound right or should I plan for less?

The stack up is water pump impeller, gasket and divider plate.

[Formulas]

I never measured mine I just used a hammer without a gasket evenly tapped plate down to contact with cast impeller then tapped it back to a no rubbing point and then the gasket provided additional clearance when fully assembled

[78w72]

i dont think gaskets will compress much, getting it around .050-.060 +/- .010 is all thats needed for the improvement over how they are stock or with aftermarket pumps... i do like formulas said & set the clearance without the gasket & then bolt it together & so far all my cars, even high HP, run as cool as can be with worn out stock clutch fans.

[MarkS57]

Having recently completed divider plate clearencing and restricting the bypass hole size to 5/16, my feeling is these are excellent modifications. They certainly help stabilize engine temperatures.

[Formulajones]

I've never done any of it, on any Pontiac engine. Even large CI big HP street driven stuff. Never had a problem with over heating.

[ZeGermanHam]

Originally Posted by Formulas

I never measured mine I just used a hammer without a gasket evenly tapped plate down to contact with cast impeller then tapped it back to a no rubbing point and then the gasket provided additional clearance when fully assembled

This is the mostly approach I took with my car, although I didn't tap it down so far that it rubbed initially. I Just got it tapped down as evenly as closely as possible to not rub when bolted down and called it good. I don't think it needs to be any more complicated than that. The water pump bolts are only tightened to 10ft-lbs if I recall, so the gasket isn't going to compress a ton.

[grandam1979]

Originally Posted by Formulajones

I've never done any of it, on any Pontiac engine. Even large CI big HP street driven stuff. Never had a problem with over heating.

I have never worried about it either I have checked the last few I assembled after all the horror stories but never had a overheating issue. When it gets cold I have blocked half the radiator to get heat in it.

[geeteeohguy]

I don't measure mine, but I set the gap at 1/8". Never had an issue (all 8 bolt early engines). I also have had good results spraying Glyptal insulative coating on the divider plates and on the inside of the timing cover so they won't fall prey to corrosion via electrolysis.

[tooski]

Originally Posted by Formulajones

I've never done any of it, on any Pontiac engine. Even large CI big HP street driven stuff. Never had a problem with over heating.

I've done it on two engines. Different power levels. Didn't make any difference.

[Formulajones]

Originally Posted by geeteeohguy

. I also have had good results spraying Glyptal insulative coating on the divider plates and on the inside of the timing cover so they won't fall prey to corrosion via electrolysis.

That's a good idea

[Jay S]

Imho...Anything less than 1/8” should be fine, trying to narrow it exactly to .050 is a bit of a waste of time. The tighter clearance helps the water pump move coolant at low engine speed (idle). At the very least it can help the heater work better at idle or possibly help the engine run slightly cooler idling at a stop light. That tighter clearance does nothing at cruising rpms. Reman and new water pumps often have the impeller pressed on at the incorrect distance, it can happen across most all engines. Even modern engines. At low speed it becomes inefficient , all the flow is going through the radiator, not enough flow left over to recirculate coolant thru the heater core. If it is really bad it can cause heating issues at idle.

[tom s]

I have NEVER even looked at the clearance!Tom

[Vid]

I payed close attention to Jim Hand’s book with last 400 I built, and weirdly enough when I did a preliminary slap together of the water pump the clearance was sitting pretty at .050. Sometimes you just get lucky


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[Charlie Brengun]

I just replaced the waterpump in my GTO and set the clearance to around. 060
The previous waterpump had a stamped impellar and the clearance between the plate and the pump resembled a canyon.

[Cliff R]

I've never checked clearance on mine but I do pull the factory cast iron impeller off of it and re-use it on the rebuilt pump I get from the parts store. I will NOT use any of these pumps with a stamped steel impeller on them......

[MarkS57]

Originally Posted by Charlie Brengun

I just replaced the waterpump in my GTO and set the clearance to around. 060
The previous waterpump had a stamped impellar and the clearance between the plate and the pump resembled a canyon.

This was my experience with an 8 bolt pump. I'll also say before the mods my 400 didn't overheat but the temp would creep above the 180 t-stat temp in traffic etc. Now, with the canyon rectified, it stays at 180 all the time.

[johnta1]

Cast impeller clearance

I thought this was a sticky at one time?

Anyway, lots of info in the thread linked.

[Formulajones]

Originally Posted by tom s

I have NEVER even looked at the clearance!Tom

Me neither

[lust4speed]

Do you guys apply the same logic to timing, deck height, and a few other engine items?

Ok, just rattling cages, but altering the plate clearance is a worthwhile endeavor.

Granted you can get lucky and have decent clearance, but I've yet to find a setup that didn't need some tweaking. Larger clearance between impeller and plate is simply wasted efficiency and even introduces the possibility of cavitation. Most wouldn't install a fan shroud with excess clearance between radiator and shroud and this is no different.

...I just used a hammer without a gasket evenly tapped plate down to contact with cast impeller then tapped it back to a no rubbing point and then the gasket provided additional clearance when fully assembled...

Pretty much what I do. It also helps to compress the plate the complete width of the impeller blade and not just the inside lip. Jim Hand mentioned he goes for .050" clearance, and that just about happens to be the thickness of the gasket. So altering the plate without the gasket in place gives the proper amount of clearance when the gasket is added.

[Formulajones]

That's an interesting one too. I've never found any difference between cars with regard to fan blade spacing and shrouds either. As much as that's been talked about in magazines for decades (long before the internet) relating to all brands of cars, I would have thought there was something to be had there.

We have about a dozen cars here and they all vary wildly with regard to engine fans and distances between radiators and fan shrouds. Some are all the way in the shroud, some are barely out of the shroud, (one with no shroud) and none of them are all that close to the radiator. Not a single car exhibits the half in/half out scenario that is so often preached about, and they are all factory setups. I don't have a heating problem with any of them. So I gave up on that theory too.