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Repairing a Leaky Oil Cooler 

new 3/8/2004, updated 02/10/2005

I took a stab at repairing a leaky oil cooler instead of buying a new one.Larry asked me for a thorough write-up on what I did so here it is.

Picture 1 - Wide angle view of a V8 with arrow pointing to the Oil cooler. On a motor IN the car, this cooler will be up UNDER the front exhaust manifold. Unscrew the oil filter and let the oil drain out of the cooler. Unplug the wire going to the Green Switch.

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Picture 2 - Close-up on the cooler. There are 3 bolts which hold it on to the Block. There is a gasket between cooler and block. The rubber hoses are antifreeze lines. I clamped them off to prevent leaking when removed from the cooler barbs. Hoses are secured by simple spring clamps.

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Picture 3 - This is a side view of the cooler. The green thing is the oil pressure sending unit.

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Picture 4 - The oil pressure sending unit and gasket were removed from the cooler before cleaning. Do Not use a channel lock or pipe wrench on the sending unit, you may damage it, causing malfunction or leak.

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Picture 5 - Invert the cooler and place it in a vice for disassembly.

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Picture 6 - This nut on the inside of the cooler holds the oil filter and also hold the cooler to the sending unit casting / elbow. It is a 30 mm nut and it is TIGHT. (Probably Loc-tited) 

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Picture 7 - It is awkward getting a wrench to grab this nut properly so be careful.

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Picture 8 - I took a spare offset head 30mm box end wrench I had laying around (WHAT!? Doesn't EVERYBODY???) and ground out the bottom with a dremel wheel to get the wrench to seat properly on the Stem, which is recessed in a channel in the cooler

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Picture 9 - The arrow points to 2 positioning ears on the oilcooler. A cast ear from the sending unit elbow fits between them when all is properly aligned. When you are loosening the 30mm Stem it is important NOT to allow the cooler section to rotate and bend these positioning ears.

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Picture 10 - 30mm Stem unscrewed

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Picture 11 - Oil sending unit elbow separates from the oil cooler body after the 30mm Stem is unscrewed revealing the factory "O" ring which is the source of my leaking.

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Picture 12 - I selected a round "O" ring to replace the factory "Flat" ring. The factory ring is silicone and .085 thick. My ring is 3/32 sidewall x 2 " ID. It comes out to about .1 thick. Just a tiny bit MORE crush than the factory ring i.e. tighter seal.
The material I selected is called VITON. It is highly chemically resistant and rated for 450' F temps. I ordered a 10 pack of these "O" rings for $7.00 from the McMaster/Carr Company. VITON is IMPORTANT - "Regular" Rubber "O" rings I would NOT Trust.
Look INTO the barbs that the coolant hoses attach to. Make sure that there is no obstructions in here. My cooler was completely PLUGGED by hard water scale and needed to be cleaned out before proceeding.

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Picture 13 - I put the new "O" ring into the slot in the cooler after a very thorough cleaning and a final wipedown with alcohol. I then covered the "O" ring with a fine layer of Permatex Ultra Gray sealant and reassembled the oilcooler to sending unit elbow.

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Picture 14 - I used Red Loctite (Permanent) to secure the Stem that hold it all together - Don't want THIS coming loose, remember THIS is what your oil filter screws on and off of every 3000 miles.

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Picture 15 - The red arrow points to the seam between the oil cooler and elbow casting. I smeared a fine layer of Ultra Gray around the Outside of this seam as additional insurance. Allow plenty of time to dry and put back on car. Don't forget to reattach the oil sending unit. This cured MY leak. Cost ~ $10.00. 

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Eric Lehmann

When Eric talks about the one side being completely clogged, he was not kidding. I saw it and it was not pretty. One side was just packed with "mud". No way coolant was going to circulate there. Thanks Eric for a great write up. 




Fixing Phase II

The article on fixing a leaky oil cooler is great but I am lazy. I did the fix in about 1.5 hours this way. I ran the car up on my ramps to get some room, took off the under panel [ tools: 5.5mm socket 8mm socket] by removing the 11 small screws and the three larger ones. With the panel off I drained the radiator, I don't like Prestone showers. Remove the oil filter and let the cooler assembly drain. When I ordered the vitron O-rings from McMaster Carr I ordered a 30 mm deep socket $ 12.00. I removed the stem assembly with the socket and then removed the cooler assembly. Make sure you flush the water jacket as the gunk in the line clogs the line tight. Clean both the cooler surface and the flange surface. I used a piece of red Scotch brite wet with solvent. I used the copper for a gasket to keep the O-ring in place and to seal both surfaces together. Installing is the reverse removal. Since it so easy to do I believe that it should be part of regular PM (10K) to insure the engine oil cooler is working properly.

my $ 0.02 worth


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