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I have been wrong and it has been incorrect for all of these years!

idrivemopar

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I will try to make this as short as possible, but its a story that spans several decades.

Back in 1983 I bought my 73 Roadrunner. with its original 340. When i got it, the AC didn't work, and so the drive belts for the alternator were routed around the AC compressor. It was never used until I did the restoration in 2011 to 2014. So when i drove it back in the 80's I always had problems with the heater hoses leaking, the radiator, and heater core leaking But i didn't think much of it because I swapped out the motor with a 318 in 1987 and the problems went away and the 340 engine then sat until 2011 when i went and got it for the rebuild.

So fast forward to the past few years after the restoration was completed. I started having some similar issues! The heater valve started leaking and eventually cracked in half, a strange whistle noise always was coming from the front of the motor, I have had this strange vibration at 3200 rpm that made no sense, and I have replaced two water pumps in 1000 miles. One failed because the impeller shaft moved forward and started rubbing on the inside of the housing and the second one started leaking from the weep hole in less than 500 miles. Both were new Mopar branded Chrysler part number water pumps, and were the same heavy duty housing that looks like a Gatling gun and has an 8 blade 4 inch impeller. These both matched the one that was on my 340 when i took it out back in 1987 so i assumed this was the correct pump. Thinking that maybe the failures were do to the increased horsepower after the rebuild, i ordered a high performance Edelbrock water pump. During installation of this pump is when the light went off!!!

I bolted on the Edelbrock pump and all looked good until i ran the AC compressor belts. The belts both rubbed on the side of the pump housing. According to Edelbrock this pump fits all small block applications! LOL, no, it doesn't and they didn't have any answers whatsoever for me when i called their tech line! So, i wondered, how did was the clearance on the heavy duty housing pumps. I pulled all three and began inspecting them and hey guess what, they all have rub marks, including the one that was on the engine back in the 80's; it was very worn on the housing. So I thought this cant be right, what do i do now, check the specification in the service manual of course! Well duh, I've been shooting myself in the foot for all these years because i overlooked one simple detail.

According to the specs for 1973, there are only two engines that use the heavy duty 8 blade 4 inch impeller water pump, the standard 318 and the Police 318, but not the 340, even with the max cool option, it requires the standard housing 6 blade 3.75 inch impeller. So I went and got a brand new Carquest standard 6 blade impeller pump, installed it and guess what! The belts have almost 3/4 inch clearance to the housing, no more whistling noise(which now i believe was caused by the belts rubbing the housing), the strange vibration at 3200 rpm is gone(i think excess pressure/cavitation in the pump may have caused this as well as the failures of both pumps). The engine is running smooth and quiet under the hood.

After all these years, i was wrong, assuming that what was installed was correct when it turns out it was completely wrong. Thats a long lesson learned.

Don't always believe what is installed is the correct part and always check the obvious, which is the specifications!

If this saves one person from this kind of frustration, then my job is done here!
 
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That is good that your problem is solved. However I have never seen external pump differences and the impeller should have zero vibrations no mater the vane or diameter. Cooling issues both ways can be attributed to impellers. Do some research on the questionable pump it could be some industrial or marine application that had reverse rotation. Those pumps could have physical outside differences along with a design for opposite rotation..
 
Gotta love an "easy" fix.
 
I does not take much negative pressure to raise the boiling point and cause the pump to cavitate
And the water hammer will damage lots of stuff
 
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