Per usual, I am up to no good
More specifically, I've been rustling around with water pump parts, which is never a good sign! This is going to be a long post but I feel that the backstory is important here to explain why I've started messing with this.
I have always been interested as to why Jane has run cool as a cucumber in comparison to "everyone else's" cars. It seems somewhat unfathomable that a 289, bored 0.040" over, with a hot cam in it, should run as cold as it always did. I always had a stock cooling system with a stock Motorcraft 192*F thermostat, stock water pump, stock brass 3-row radiator, and stock fan clutch + 7-blade fan. I mean STOCK! Despite this, the car would sit at idle in traffic for hours on end in 100*+ temperatures, with the A/C on, without breaking a sweat. Never rolled above 203*F.
Well, I refreshed the engine last year. Bore is the same, cam is the same, compression is bumped up half a tick but that's about it. All the parts match now, which is an improvement. At the time I also swapped to an aluminum radiator (the brass one got clogged and it cost the same to swap to a higher-quality aluminum radiator as it would have to rod out the old radiator) and put on a new water pump.
And now, somehow, the car gets a little warm at idle, and does it quickly too. You drop to idle and it will be up over 200*F within a minute. Never overheats and I have yet to see it get above 215*F, but still behaving abnormally compared to before. So I started looking for reasons why.
Well, I know it's not the new radiator. When I'm moving on the highway, I even have a hard time keeping the engine warm sometimes. So I can throw that out the window.
I know it's not the thermostat. I have a very accurate temp gauge, and it shows the thermostat in good working order. Furthermore, at lower ambient temps / on cloudy days, or when moving, she'll sit right at 190-192*F all day long. So I can throw that out the window too.
So that leaves one thing: the water pump. Now, what's in there currently is a Carquest pump. It fits, and it works, so those are both good things. However, I noticed that the impeller on the backside of the pump is one of the star-shaped open 6-vaned impellers. On the pump that I pulled off of Jane, the impeller is closed and has 8 vanes.
That kind of got me thinking: why are these impellers different? What's the benefit of closed vs. open, and number of vanes and orientation?
Interestingly, the Flowkooler pumps, which are touted as being able to reduce your engine temp significantly at any speed below 3000 rpms, utilize a closed impeller with 16 vanes. So maybe this is a water flow thing. Reduced cavitation and better linear flow would both be good for cooling. So maybe, just maybe, there's more to this than has been previously considered.
Now, for this impeller on Jane's pump: I looked just about everywhere to try to figure out where this thing comes from. The factory HiPo cars used a 6-vaned closed impeller, not one with 8 vanes - and they've got a different hole pattern and diameter. Most reman pumps sold today just use that star-shaped open impeller. So where the heck did this thing come from? More importantly, how would I find a new one? I wanted to test the effectiveness of this impeller vs. the open ones, but my old pump was definitely approaching "trashed" - all kinds of corrosion and wear - so I didn't want to put it back on.
I ended up sending my pump off to Wade at Flying Dutchman Water Pumps in Oregon. I contacted him and told him about the impeller I was looking for, and he immediately knew what I was talking about. He said he actually has one in a Bronco of his and that it dropped the car's idle temperature by 25 degrees when he replaced the generic parts store open impeller with this old OEM part. Apparently this 8-vane impeller was used on some early 260s and 289s (the ones without the water pump backing plates) from the factory. He believes that they were on HiPo cars. It is not reproduced, which is why you don't see it on pumps today.
Anyways, he happened to have one on hand and put it on Jane's old pump. He also installed a new bearing and resurfaced the pump body because the angle of the impeller was out of pitch. It looks awesome! Can't wait to install it and try it out.
He also sent back my old impeller at my request. I wanted to take some pictures of it, since I haven't been able to find any on the internet (a first!). More importantly, if the freshly rebuilt pump ends up changing how Jane's cooling at idle back to her "normal" state (cool as a cucumber at all times), then we'll know why and I will have the culprit on hand. If there's enough interest, I'll find a way to get it reproduced and then everyone can quit with the "my Mustang overheats all the time" threads here on VMF
Of course, this could all be an endeavor in which I'm just chasing my own tail, which happens sometimes. Even if it is, at least I've got documentation of this interesting different part, which is not listed anywhere I can find it. But if this does end up impacting low-RPM cooling, then I'll be able to contribute to the solution to what is arguably the biggest "problem" that people have with classic Mustangs!
Pics of the mysterious impeller (obviously, the corroded one is the old one, and the silver one is the new):