Hemi Leaker

I bought a Mopar Performance 472 Hemi in 2000, and I stuffed it into a ’68 ’Cuda. Upon firing it up, the rear main seal leaked like a bad faucet. I’ve heard rumors to put .015-inch shims behind the rear main seal. I also bought the aluminum bridge and seal from Indy, but before I tear it apart to fix the oil leak, I wanted to get your take on the situation. Any information would be greatly appreciated.

Brian Moryc - Via email

Brian, I think if you have already gotten the Indy seal retainer, you are best off following their recommendations to the letter. I would not run any kind of shims behind the seal. The back of the seal must seat solidly against the retainer, and putting some kind of shim stock back there would virtually guarantee a leak. The key is a perfectly clean surface and attention to detail. With the stock style seal retainer, I have had the best luck by lightly surfacing the mating area at the base, and using a Fel-Pro Viton rear seal, number Q-2947, and the OEM-style fiber side packing. I make sure the retainer and block mating surfaces are perfectly clean and oil free. I bed the rear seal into the retainer and block with a dab of Hylomar sealant. I use a light film of silicone sealer on both the retainer and block side where the side seals slide in, lightly lube the lips of the seal, and then install the retainer loosely with the fasteners finger tight. Then I put a light coat of silicone on the side seals and push them in until bottomed. I finish by torqueing the two retainer bolts. This process has always resulted in a leak-free installation for me.

Hot Street Demon

I have a ’71 Demon with a 340 and a four-speed. The 340 is stock except for the carburetor. The problem I'm having is the temperature spikes when the rpm is above 2,500. When the rpm comes down below 2,500, the temperature comes down to normal. This started one day after a short drive. I thought it was the thermostat, so I changed it, but it did the same thing. I took the thermostat out to check the circulation of the coolant, and the pump is circulating the coolant. The radiator is new, and it’s been in the car when temperature was normal before it started acting up. When I shut it off after a drive and it is fully warmed up, I get a slight drip of coolant from the overflow hose by the radiator cap. The temperature gauge shows normal, not overheating. Do you have any ideas? Maybe a head gasket?

Todd Mullin - Via moparmusclemagazine.com

Todd, I don’t think it is the head gasket, but you can start by pressure checking the cooling system. If the head gasket is blown, it will not hold pressure. You can make a preliminary check by just looking for signs of compression bubbles in the coolant with the cap off. I think you are on the right track by questioning the flow through the system. Since you already checked the thermostat, I would be suspecting a kinked or blocked lower radiator hose. This is the suction side hose, and in the old days it came with a wound spring inside to keep it from being sucked closed and collapsing. Unfortunately, most new parts house hoses do not come with this spring, making this a common problem.

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