MrBuick (Magnum)
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- Benton Harbor, MI
- Buick Ownership
- 95 Roadmaster Sedan (3), 94 & 96 Roadmaster Wagon
MODIFYING LT1 OFFSET OIL FILTER ADAPTER TO REMOVE COOLER LINES
Written and documented by our member "paart".
The oil filter adapter on my RMW started leaking, and after two failed attempts to repair it, I decided to replace it. This offset adapter used on many LT1 engines has been discontinued for years, and it seems that there are no after-market replacements available. I obtained a used one, but it was the “oil cooler” type that seems to be more available than the “non-cooler” ones. This availability could be due to some owners removing the troublesome factory oil cooler line set-up, which is generally ineffective, anyway.
Below, is a description of the steps I used to eliminate the cooler “loop”.
The oil flow within the adapter is:
1/ Output from the pump is routed to the filter “in”. (outside ring of filter holes)
2/ The output from the filter (threaded, center filter opening) goes to the cooler line marked “OUT”.
3/ The cooler return (IN) line empties into the “upper chamber” of the adapter which supplies the engine with oil.
There is a bypass valve installed between the filter output and the chamber, to insure oil supply, if the external cooler would clog. This safety valve would allow engine operation with the output lines blocked off, but adds restriction to oil flow, and could fail closed and stop oil flow completely, probably causing catastrophic engine damage, so I decided to remove it, and “cap” the lines.
The cooler bypass valve is located directly above the filter nipple/screw, which will need to be removed with a 7/8” deep socket. Mine came out with hand pressure on the socket.
After placing the adapter on wood blocks to protect the filter mating surface, I removed the valve with 3-4 good “whacks” with a hammer and drift. Remove only the bypass valve visible under the removed nipple. Do not remove the other check valve, as it opens only when the filter clogs. Removing it would bypass the oil filter at all times.
The output lines are the compression type which cannot be easily closed off directly. The best way to close off the ports would be to install a 3/8” pipe plug. Unfortunately, this requires drilling with a 37/64” bit for tapping, and that’s not a common size. If you elect
this option, it might be better and cheaper to have a machine shop drill and tap the holes. I found that a 1/4” brass (not iron) NPT plug will just start and cut light threads in the opening. Working the plug slowly back and forth created threads deep enough to keep the plug amazingly tight. But, I wouldn’t trust it enough to bet my engine on it, particularly as the aluminum adapter expands from heat. So I coated the plugs with JB Weld. I allowed the epoxy to set, cleaned the adapter with solvent and air, installed the filter nipple, and it was good to go. I doubt it adds much, but for extra insurance, I ground the cooler block pipes off, and installed it over the pipe plugs, using the center mounting stud and nut.
Tips: The adapter mounting allen head bolts are ¼” not 6mm—use the correct size, or risk rounding off the bolts.
Torque the bolts to 17ft/lbs on installation, using a socket with a long enough allen wrench, so that the socket body doesn’t rub against the adapter body, changing the torque reading.
Hold the rubber o-ring in the groove with light grease.
The GM O-Ring and gasket appear to be of better quality than the Dorman item, and at a lower price. The Dorman set includes 15 unneeded o-rings.
Written and documented by our member "paart".
The oil filter adapter on my RMW started leaking, and after two failed attempts to repair it, I decided to replace it. This offset adapter used on many LT1 engines has been discontinued for years, and it seems that there are no after-market replacements available. I obtained a used one, but it was the “oil cooler” type that seems to be more available than the “non-cooler” ones. This availability could be due to some owners removing the troublesome factory oil cooler line set-up, which is generally ineffective, anyway.
Below, is a description of the steps I used to eliminate the cooler “loop”.
The oil flow within the adapter is:
1/ Output from the pump is routed to the filter “in”. (outside ring of filter holes)
2/ The output from the filter (threaded, center filter opening) goes to the cooler line marked “OUT”.
3/ The cooler return (IN) line empties into the “upper chamber” of the adapter which supplies the engine with oil.
There is a bypass valve installed between the filter output and the chamber, to insure oil supply, if the external cooler would clog. This safety valve would allow engine operation with the output lines blocked off, but adds restriction to oil flow, and could fail closed and stop oil flow completely, probably causing catastrophic engine damage, so I decided to remove it, and “cap” the lines.
The cooler bypass valve is located directly above the filter nipple/screw, which will need to be removed with a 7/8” deep socket. Mine came out with hand pressure on the socket.
After placing the adapter on wood blocks to protect the filter mating surface, I removed the valve with 3-4 good “whacks” with a hammer and drift. Remove only the bypass valve visible under the removed nipple. Do not remove the other check valve, as it opens only when the filter clogs. Removing it would bypass the oil filter at all times.
The output lines are the compression type which cannot be easily closed off directly. The best way to close off the ports would be to install a 3/8” pipe plug. Unfortunately, this requires drilling with a 37/64” bit for tapping, and that’s not a common size. If you elect
this option, it might be better and cheaper to have a machine shop drill and tap the holes. I found that a 1/4” brass (not iron) NPT plug will just start and cut light threads in the opening. Working the plug slowly back and forth created threads deep enough to keep the plug amazingly tight. But, I wouldn’t trust it enough to bet my engine on it, particularly as the aluminum adapter expands from heat. So I coated the plugs with JB Weld. I allowed the epoxy to set, cleaned the adapter with solvent and air, installed the filter nipple, and it was good to go. I doubt it adds much, but for extra insurance, I ground the cooler block pipes off, and installed it over the pipe plugs, using the center mounting stud and nut.
Tips: The adapter mounting allen head bolts are ¼” not 6mm—use the correct size, or risk rounding off the bolts.
Torque the bolts to 17ft/lbs on installation, using a socket with a long enough allen wrench, so that the socket body doesn’t rub against the adapter body, changing the torque reading.
Hold the rubber o-ring in the groove with light grease.
The GM O-Ring and gasket appear to be of better quality than the Dorman item, and at a lower price. The Dorman set includes 15 unneeded o-rings.
