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Old 05-26-2024, 02:55 PM
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Coolant "return pipe' leaking on 4.8IS

Hey all. I had a leak coming from the short rubber-coated return pipe that connects between the water pump and the coolant neck on the valley pan. It was because the rubber was cracked and peeled somewhat on the old one. I replaced the tube with a new one and it was dry for a few days but started a small leak exactly where I had the last leak; the bottom of the tube where it meets the valley pan neck. Getting frustrated, what could it be? I did not by an OEM part, could that be it?
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Old 05-26-2024, 03:08 PM
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Did you replace pipe and gasket and did you polish the sealing surfaces where the gasket mates?

I reused original pipes doing a chain guide job on 4.4 and was able to polish the ends to a mirror finish before reinstall. I forget exactly what that seals against but I think it's the coolant crossover in back and water pump in front.

Is that the pipe/s I recall two pipes in the valley did you replace both and did you take off the intake to get a good lol or just looking at the bit you can see over/past the pump?





Found photos looks like maybe go into the back of thermostat? Maybe the b failed seal is between gasket and thermostat.

Realizing that I polished the protective oxide later off the bare aluminum pipe I sprayed paint up to the seal.

One theory of failure on that seal is that environment works its way under the seal from the outside and since it's not accessible once installed I painted over the seating areas on the outside.

You may need to use some UV dye to track the exact leak if it's small.
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Old 05-26-2024, 03:13 PM
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Re: OEM. Always possible. I'm guessing you didn't match up to compare exact length and OD with a caliper. It's a known fussy joint so a small error could be the cause of the leak.

My thought is if possible with minimal tear down would it be possible to loosen parts enough to twist the pipe to get a better seal without disassembly?
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Old 05-26-2024, 05:27 PM
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I measured OEM vs aftermarket cooling pipes for mine. The OEM pipe ends were larger. All other hoses didn't matter. Easier to reach or replace o-rings without removing the intake. My lesson, if it goes to the block go OEM.
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Old 05-26-2024, 06:33 PM
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I had a large pipe leak on my 4.6 at 11k. I am fairly sure itís because I used eBay pipes to assemble the motor. They werenít perfect, but I felt they cleaned up nicely with progressively finer wet/dry sand paper. I also used some water based lube to ease the assembly and not roll the o-ring. I feel that may have hardened in the heat though.

Iím not sure there is any easy way to quick fix this stuff, if the 4.8 is anything like the 4.4/6. The entire intake needs to come off.

At any rate, I bought a new large pipe, new seals and used antifreeze to lube it. So far so good but itís only been fixed for a couple thousand miles. Frankly the small pipe looked worse when I assembled it all originally, but it wasnít leaking. This is good because this piece isnít available OE new any longer.
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Old 05-26-2024, 07:39 PM
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This is a completely different component on the N62 vs M62

I used an aftermarket pipe on mine and no leaks. I did clean the inside of the area and used a little coolant on the sealing surface when I inserted it. First into the block, you should sort of feel it pop into it's position once seated fully. Then the waterpump/thermostat onto the pipe - again you should sort of feel it settle into it's spot and it will even help hold the water pump assembly in position.

I would take it back apart and inspect the sealing surfaces fully. There's really not much to it - I think the most likely cause of it leaking is not using a little coolant on the pipe when installing. This can cause it to pinch or just not seat properly which can cause a leak to develop after a few heat cycles.
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