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A few years ago I replaced my leaking '67 water pump with a FlowKooler water pump. I was very discouraged to find that the cooling performance with this new pump was very poor when compared to my old original set up. On a couple occasions in creeping traffic the car got up to 235+. The temp also crept up when cruising 60 mph or faster. Due to the "getting too hot" situation with the Flowkooler, I added an AC style shroud and replaced my original fan clutch, but this didn't help.

(By the way, my configuration is a totally stock YS 400 engine in a totally stock '67 GTO.)

Finally this past winter I bought some gaskets and took the FlowKooler pump off to see what was going on.

Firstly, I checked the distance of the rear plate to the impeller and found it to be about 0.140"...which probably did kill off some efficiency of the pump. So yes, naturally, I peened over the rear plate port opening to get it to within about 0.040" of the impeller surface. But the main point of my post is that in addition to the impeller spacing to the rear plate, I also checked the spacing of the (8 bolt style only) center divider plate relative to the impeller vanes. The center plate is supposed to evenly split the volute into two; the rear half of the casing directs pumped coolant to the passenger side of the block, and the front half directs coolant to the driver side. The vanes of the impeller should evenly sit in both halves of the casing. What I discovered is that the center plate/impeller position was biased to almost completely favor one half only. So only one side of the engine block saw any significant coolant flow from the pump.

The solution for me was to make a new divider plate that positioned the divider midway on the height of the vanes.

Conveniently, The optimum plate shape was flat (unlike the original dished divider plate) and easy to make out of 18 gauge sheet metal. The piece was carefully trimmed to fit tightly in the waterpump housing/timing cover. This change in plate shape required closing off a slot in the rear plate. I simply welded a sheet metal patch in place. With the new plate, the impeller now straddled the center divider plate evenly, and I believe equal pumping was restored for both halves of the pump cavity.

My cooling improvements are impressive . The car can sit and idle and it does not heat up. I can travel on the highway and it stays below 195 or so, at least on high 80's temperature days.

Not sure if this center/divider plate check has been mentioned before, so I thought I'd share my findings.

Pictures: The first picture is of the original dished center divider plate on the flowkooler. Note how the vanes are mostly buried in the front half of the pump cavity. The second is of the new flat divider plate which now evenly splits the cavity. The third picture shows the new configuration in the timing cover. The fourth pic is the small patch I welded to the rear plate. And finally the rear plate to impeller distance check.

Dave