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Home » Public Forums » GMCnet » Cleaning the oil pump screen without removing the pan
Cleaning the oil pump screen without removing the pan [message #367845] Sun, 05 December 2021 19:34 Go to previous message
Greg C. is currently offline  Greg C.   United States
Messages: 224
Registered: October 2019
Location: Knoxville, TN
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Senior Member
So on the FB GMC forum, a new owner has just purchased a coach and during his travel home, experienced severe oil pressure loss. He had an oil change done with no better results, and rented a car to drive home. Since his coach is stuck at the airport parking lot in my home town, I offered him the use of my driveway, tools, and assistance to try using thicker oil just to help him get home. Evidently, he lives several hundred miles from here. He's supposed to drive the coach to my house on Tuesday, the way things currently stand. He's decided that the engine has to come out and be rebuilt, but just wants to try to get it home to save the several thousand dollars of towing/hauling. Several folks chimed in on the forum with advice. One or two suggested that oil cookies from the intake may have clogged the oil pump screen since he experienced a rapid loss of oil pressure with no discernible leaks and plenty of oil. Rick Michelhaugh, a local GMC'er, suggested pulling the distributor and spinning the pump backwards with a drill to flush out the screen. My thought on that would be that you would run out of oil quickly sucking it from the galleys and passages instead of the pan, possibly before everything (if there is anything) could be dislodged.
I ran across a device that was patented in 1996, since expired, that consisted of an adapter plate for the oil filter housing, a container of oil that can be pressurized, and assorted plumbing. The patent states that the device will push oil through the housing, through the passages, and backwards through the pump, flushing crud from the screen. Additional valves allow air entrainment of the oil to act as an agitator.
My first thought on that was that the gears in the pump would have such close tolerances as to prevent the oil from flowing past a non-moving gearotor pump, but obviously the guy who spent several thousand dollars to get a patent must have been pretty sure it worked.

So this adapter will be easy to make on my lathe. An old portable air tank can have a screw on lid welded to it for the addition of oil, and some ball valves and hoses would complete the device. The patent called for a maximum pressure of 40 psi to prevent damage to coolers, gaskets, etc.

So I'm going to make the adapter plate so we can flush air through it at the least. If I can find an old air tank and have time to fabricate the rest, I'll do that too before he gets here. I figure the only thing we have to lose is time, and wouldn't it be great if that was the problem and it fixed it?

A question: Is the oil pump screen in such a location that we could look at it through the drain hole with a borescope?

What are everyone's thoughts on this wild goose chase?

Greg Crawford KM4ZCR Knoxville, TN "Ruby Sue" 1977 Royale Rear Bath 403 Engine American Eagle Wheels Early Version Alex Sirum Quad bags

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