The '71 with the new motor always ran hot. And by hot, I mean 200-210 degrees while driving 80MPH when the temp outside was in the 40's. The last time I drove it during the day, it rose to 220 degrees and it was only 80 degrees outside. Not good.

Pulled the water pump and sure enough, it had a stamped steel impeller. Went to Auto Zone and got one with a cast impeller. Even though the stamped impeller was 4" in diameter versus the cast impeller being only 3", I drove it home tonight with a 55 degree outside temp, and the guage never went over 180, whether on the freeway or the street. http://forums.performanceyears.com/g...on_biggrin.gif

very interesting......
Glad it helped...!

I've got a few words on that subject: I don't have a stamped impeller, but I do know that pump efficiency is directly related to the clearance between the divider plate and the vanes. If your clearance, (regardless of cast or stamped) is more than say, .060", YOU ARE THROWING AWAY COOLING EFFICIENCY. I tweaked mine from about .250" down to about .100" and it made a drastic change in my engine temps with no other changes.

You can spend money on big radiators, electric fans, magic cooling fluid, yadda,yadda, but if you are running a large clearance all the other stuff is a band aid. Do the clearnace thing first, then go from there. Cost is a few bucks for a gasket.

Not only that, hot start problems went away too...a possible side benefit.

George

George,
After reading your post above, it tweaked my interest enought to cause me to go out to the shop and pull the water pump to check this out. Sure nuf, about a quarter of an inch between the pump vane and the rear internal housing that allows water into the pump vane. Looks like you have hit the nail on the head! If it can't pump efficiently, all else is just for fun. I assume you just tweaked it with ball peen hammer to fit closer to the pump vane, right? I'd love to just do that and put it back together, but I'm thinking a new pump and fan clutch wouldn't hurt before I put it back together. Sure hate it when you know you should change something, then don't and it fails two weeks later! I know there is nothing wrong with the pump or fan clutch now, but if I change them I'll wonder which did the trick. Your suggestion sure does make sense AND it can't hurt. I will try it.
Thanks George, I do appreciate it.
Charles

[I tweaked mine from about .250" down to about .100" and it made a drastic change in my engine temps with no other changes.]

I agree that this sounds like a pretty good idea. How did you measure the clearance though?

I took the pump & put it upside down on the bench (obviously you have to take the pump off) put the gasket on it then the divider plate. Measure the clearance between the pump side surface of the plate and the edge of the vanes. This should be made as close as possible. I used a hammer to carefully bend the circumference of the hole of the divider plate towards the vanes.

The suction of the pump is thru the center hole, and the pressure side is around the tips of the vanes. Too much of a gap between the plate and the vanes and the pump tends to draw coolant from the pressure side instead of from the center hole (which is plumbed to the radiator and the hot side of the block).

That's why minimizing this leakage path improves flow thru the engine and thru the radiator (when the thermostat is open).

George

George,

Thanks for the additional info. I just added that to my "To Do" list once everything warms up around here. It would be great if that dropped temps enough that I don't have to spend the $$$ on an aluminum radiator.

Here is a picture I borrowed off ebay. So you are saying to bend the center section towards the impellar so there is about a .100 gap? Is it pretty easy without distorting the whole plate?

Yep, that's exactly it. Tap lightly and evenly at the perimeter of the hole. It doesn't take much. Remember to size it up with a gasket in place to give the proper installed spacing.

Measure it first; if more than .1" (approx), you should adjust it. Mine was about .25". I stopped at about .1" to make sure the vanes wouldn't contact the plate when the gasket was compressed.

George

George,
Have you had any problems with the plate contacting the vanes once it gets hot? Or is the plate strong enough not to flex with the heat?

I don't have any problems with contact. I also doubt if the plate would deflect enuf under normal temps to cause contact. I tried to be reasonable about closing up the clearance to avoid just that scenario.

A mechanical engineer can chime in here... but I'll bet that pump efficiency is VERY sensitive to small changes in gap; max efficiency at very small gaps and efficiency probably decreasing very quickly with small changes, i.e. the pump will probably be useless at a gap greater than .3" or so.

Since the vane tips have higher pressure, and the center hole has lower pressure, it doesn't take much of a gap for the fluid to take the short path around the vanes instead of flowing out to the block. Would be nice to have some hard data......

I'm looking forward to reports from yourselves to confirm or deny my results.

George

A while back i also received correspondence from Geoff in Australia regarding this subject. I'll paste it in here:

George,
I saw your comment about closing the gap between the impeller & the divider plate. I went even further than you did. Using some scraps of stainless steel
exh pipe, I cut strips about 1/4'' wide & the same length as the impeller blade & brazed them onto the back of the blades. I did one blade at a time, & carefully
ground the extension a little bit at a time until the impeller would rotate without touching the plate. I then did the next blade until all 8 were done. Clearance between
blades & plate was 0.030'' at most. What a difference! This pump cools better than the Flow Kooler.

Geoff,
Australia

Pretty innovative, I'd say.

George

Does anyone know if this works on the earlier water pumps or just the later ones? Also, George can you whip up some kind of diagram to show where and how you took the measurement. I'm still not completely clear on where and what you bend but then again, I haven't had the water pump off my pontiac too look at it. Thanks

Here is the pic with a markup showing the edge to adjust. The pic shows the convex side up. When installed, the pump vanes are under this plate. Bend this edge down until the gap between this edge and the edges of the vanes are minimum.

George

Well, I got a rebuilt pump yesterday from Cardone, because I was impressed by the larger pump vanes from my old one.

http://www.partsamerica.com/PartDeta...ype=54&PTSet=A

Tried the fit before bending the divider plate, and was surprised to see that the Cardone pump had vanes that were 3/16 " taller than the old one. The divider plate would only require minor tweaking. Will attach two photos showing the difference. Old pump first, new one next post, cause I can't figure how to attach two pics in one post.
George, I love the way you think simple. Is it plugged in? Is the ground loose? Think before you spend all day going around in circles and starting over at the beginning.
I know I said I wouldn't make any changes except the tweaking of the plate, but I just could not resist the pump with the larger vanes. Will have it running on Saturday and give you a full report then. Same everything else for now, because we can change the others easily if needed.
Charles

New pump, check the clearance. No difference in plate tweaking.

Dean, he's advocating bending the internal housing on attached photo from 67 manual.

Gang, sorry if I caused some confusion. The pic from the '67 manual is not exactly what I have since my engine is a '74 455. conceptually, tho, the plate that needs adjustment is the one that comes closest to the face of the vanes as in Charles' pix, above. In the pic from the '67 manual, the plate in question is what the book calls the internal housing.

I was unaware there was such a difference over the model years.

Interesting that there exists such a difference in width of pump vanes! Perhaps this is a good example of the idea that "the cast impellers are better"?

George

Gang,
Couldn't wait to get in here to tell the story! The only change being the new water pump with bigger vanes ($24.00) and tweaking the divider plate and I can report fantastic success with George's suggestion!
Before I did this the after market gauge was reading as high as 230 degrees, and had been for years! After I did this, the highest it read was 190 degrees. It's 81 or 82 degrees here today. Running a high flow Stant thermostat tested at its rated 160-degree opening. I decided to test the temp of the water in the filler of the radiator with two of Mama's cooking thermometers (she's NOT here!), after I returned home, with the engine still running. By the way, the flow of water from the pump is so high that if you rev the engine a little, the water hits the cooking thermometers and jumps out the top of the radiator! One cooking thermometer showed 163 and the other showed 165!!!! Therefore, we calibrated the Temp gauge to read properly by adding a 10-ohm resistor in series with the sense lead. Now it is as dead on as those things can be!
I am so tickled; I'm like a kid at Christmas when he gets his first BB Gun! When I think back on all this, I guess I never thought to check the clearance of the divider plate to the pump vanes years ago when I replaced the original water pump!! Just ASSUMED it was the same configuration! There's that word again! Dad was right.Think, Son, Think!
To George I owe a great THANK YOU, you caused me to start using my head.
To the other guys that make money on radiators, I am sorry, but I won't be buying a $500 radiator.
Have a marvelous day guys, it is now SPRING!

That's great to hear yet another success story! Your configuration is better yet, since the vane area with your new pump is even greater.

George