M725 blowing apart oil filters!

Okay, for those of you who don't know the story, my M725 hasn't really driven in a LONG LONG time, sitting in a field. I have been slowly rebuilding it. Well, now it sits at the brake shop, ready for some work to be done on that end. But, the shop owner wants to idle the truck into the shop, and to do that, it must run.

No problem, it's done that before. Sorta.

He ran it a couple times, and each time the oil pressue is so high that it blows the oil filters off the block. Over 150 psi or so, he tells me. He says that there usually is a pressure relief valve or something to prevent that, but he's not sure about the design of the engine, so he can't be sure.

Help?

There should be a relief/bypass valve in the filter itself. If it has a visible spring in side the filter, then it has one. Just about all modern, name brand filters have them today. If it has one and it's still blowing the filter, then you have some sort of blockage in the system beyond the filter.

What do you propose I do in order to correct the problem? Or rather, what series of steps should I take to narrow down where the problem lies in the oil system?

I'd try to see if you are getting oil pressure to the head. Since you didn't specify, I am assuming you have the original 230 OHC engine, which is famous for issues with the oil line to the back of the head. Take the cover off and run it and see if you are getting a good amount of oil to all the valves in the head. It's not uncommon for a spun cam bearing to block the oil galley and cause pressure to backup. If there's no oil at the head, remove the line and see if it's collapsed or has a blockage. If you can't find anything there then check the oil pump and make sure if it does have a relief valve, that it is working correctly. If you still don;t find anything, I'd have to say to go ahead and tear it down and check the main bearings as they can block passages the same as the cam bearings.

It may seem drastic to do a tear down, but if you can't locate the problem in the head then you probably will have to take it apart. One way or another the oil supply is getting blocked or over pressurized by the pump and unless it's corrected, you are either starving some part of the system for oil, or are over pressurizing it which will lead to filter and possible pump failure as well as foaming issues that can cost you the engine anyway.

You may also want to check with the guys at The Zone to see if they have run into this problem in the past. I had a similar problem on a '84 Ramcharger with a 318 but it turned out to be poor quality Fram filters. I no longer use that brand after having two burst the seam. The stock Mopar filter worked great, however. Just my .02

To add to what Lanty wrote.

The oil line to the head is part of the T fitting that holds the oil sending unit. If your pressure is crazy high, then I would also suspect the head oiling. Pull the valve cover and see if there is any oil there. I really suspect the line to the back of the head just because they are made just like brake lines and they can collapse.

That line is a pain to even see, much less remove. It can be done. It is normally easier to remove the bottom end by the oil sender and then with an open end wrench, rotate the elbow the top of the hose screws into until it is out. Put a new one back in the same way.

Did you install a brand new oil pump or a high flow or high volume unit?

I had a similar situation on a 318 when the oil was blowing out from between the block and the oil filter adaptor. And that was with 30 weight. It didn't help that it was the dead of winter. Had to drop the pan, take out the new pump and cut a coil or two off the spring that presses against the pressure valve. Cold oil pressure dropped from 110psi to 60psi. Warm weather driving psi was not made critical. I hope it works out.

I posted there. No responses yet.

Sigh. This resto is more work than it's worth. Every time I turn around, the 15-yr hibernation it took in the back lot of the junkyard sitting unused has taken it's toll, and everything has needed a twice-over in order to make it work. I wonder sometimes if restoring this beast is worth my time, money and effort...

I was told a year ago by the -715Zone guys that "you DO NOT want to rebuild this engine, it is an expensive and time-consuming task". Now it looks like I may have to do just that.

Its just a flat head. Its like a lawn mower times six It probably would have been more desireable to rebuild the engine & mechanicals first but stuff happens. Any local buddys that can help you? If little to no machining is required and you had all the parts lined up you could rip it out, clean it, rebuild & measure it, and run it in the truck in a weekend.

Well Video maybe. I want to see a filter explode


Hope you get this fixed without too much trouble.

Re: RE: M725 blowing apart oil filters!

No.2Diesel said:

Its just a flat head.

Click to expand...

Negative, it's actually a single over head cam, 230 c.i. inline 6 cylinder that was pretty sophisticated for it's early 60's introduction. It's a decent engine and makes good power, but is very hard to find internal parts for and they have less than half the parts in common with it's civilian counterpart.

RE: Re: RE: M725 blowing apart oil filters!

Woah Lookout!! I stand corrected. I keep thinking of the M37s motor.

RE: Re: RE: M725 blowing apart oil filters!

It's actually a common mistake. I think the engine size is similar and they both used the NP200 transfer case. The biggest difference other than the obvious fact that one is a Dodge and the other is a Jeep, is that the M37 is 3/4 ton and the M715 is 1 1/4 ton. I still think the M37 looks better but the Jeep is built more solid considering the standards of the time. I miss my M715 but I don't think I'll own another, nor will I own a M37.

RE: Re: RE: M725 blowing apart oil filters!

An update - just got a call from my mechanic since the brakes are done. He fixed the problem, said after he opened up the oil pump on the side of the block, it was all clogged with old garbage oil and sludge, and the pressure relief valve was toasted. He pulled the unit, rebuilt it, and runs like new. Starts around 90 psi, and when it warms up, drops down to 60 psi or so. GREAT!

RE: Re: RE: M725 blowing apart oil filters!

Nice job!