Oil Pressure problem (maybe)

[SoylentGreen]

Got a '72 M35A2 LDT-465-1c Whistler. 35,000 on odo. 215 on hour meter. Oil looks fresh.
Did a lot of searches and got lots of good info but still not sure what's up. Maintenance manual is on order.
I was getting a very low pressure indication so per the info I got here I installed a Sunpro mechanical guage.
When I start up it pegs out at over 100 psi (idle at about 750-800rpm) for about 5mins. then slowly starts to go down.
When I hit the road it drops to about 60psi for the first 5-6 miles at 45-50 mph then goes to 20-25psi. From then on it stays around 20psi and idles at about 15psi.
Other than that it runs great, starts right up, temp. is good.
What might be going on here?
I'm planning on a 600 mile round trip in a couple weeks and thinking I might have to cancel if I can't figure out what's going on by then.

 

[Westech]

well sounds a tad low while running down the road. could be the spring in the oil pump pressure regulator going south. When it heats up its loosing its spring... Just thinking out loud. I would not thing there is any internal engine problems due to the high starting pressure.

 

[gem1410]

One of my trucks does the same thing--I can here a little knock also when the pressure drops to 10psi--will have to drop the pan and see if something is blocking the pump or it may be bad--good luck with yours

 

[SoylentGreen]

Do you guys know where I might find a NOS oil pressure regulator?

 

[jatonka]

I wonder if you might want to do an oil change, putting in 30 wt diesel engine oil? Those little plastic springs in your 15w-40 oil might have worn out. Just a thought. JT

 

[cougarman]

My truck seemed to be the same way & found the cause...

I just posted 2 nights ago about almost the same thing. I hope you have better luck than me. I pulled the oilpan & I don't know how this engine had any oil pressure or did not knock all the time. The three rod bearings I pulled did not look too bad but the mains......wow. I could move the crankshaft about 1/4" toward front to rear of truck before I pulled any caps. I pulled three main bearing caps & it looked like the bearings spun from where they belong. Two of them had the oil hole toward bottom-not good. I have seen spun bearings before but none of the caps were blue & no damage to crank that I can see. The thrush bearing cap looks like one side was ground down though. My truck is a 68 with a Hercules engine with 24000 miles on it.

 

[SoylentGreen]

It ended up I had two problems. The pressure regulator was bad but that was an easy fix. Then after a while I figured out the fuel density compensator went bad as well and dumped fuel into my oil. I bypassed the FDC, drained the oil/fuel mix (7.5 gallons), put in fresh oil and now all is well at least for now.
Good luck on yours.

 

[cbvet]

SG,
How did you determine the pressure regulator was bad, & how did you fix it?

 

[SoylentGreen]

I think they are supposed to limit pressure to around 70 psi and since mine was going to 100 I figured it must be bad.
I replaced it with a new one from Memphis Equipment. No more 100 psi.

 

[Jeepin46]

My 1971 was leaking diesel in to the oil and dripping diesel from the Flame Heater Injection Nozzle on to the turbo. According to the tags, the engine was replaced in 1991 and the fuel injection pump was rebuilt in 1989. Rubber seals can easily harden in 20 years. My FDC was already by-passed.

Some said in the forums that the Flame Heater Injection Nozzle could cause diesel to mix with oil. I am not sure how, but what the hell, I had to replace the two o-rings anyway to stop the dripping on my turbo. I took the nozzle to NAPA and got two new o-rings for it (they cost like 49 cents). The old seals were very hard and broke when I removed them. I put the new o-rings on and installed it. I fired up the motor and drip prob is history.

Next I pulled the Injection Pump. When I removed the cover for the Fuel Shutoff it was clear that diesel was getting in the oil... the fluid was like dark diesel.

After pulling the Injection Pump and getting it on the bench, I pulled the Hydraulic Head (the thing that has the 6 lines going to the injectors). The two o-rings for the hydraulic head were mashed and sorta hard. I got two o-rings from bottleworks for $5 and got them installed. I am sure if you brought the old o-seals to NAPA they could find the right ones (they are different sizes by the way). When I was removing the Head it was clear that there was total diesel\oil mixing in the wrong places. Make sure all your timing marks are good before you pull/install that head.

Next I pulled the booster pump off the Injection Pump (the thing on the IP that has a line from the tank and a line going to the secondary filters). To pull it, you need to cut the safety wire and remove two bolts. after pulling it, unscrew the 4 machine bolts to get the small cover plate off. The seal on that was obviously hard and not going to hold back any diesel from the oil side. Again, I went to NAPA and they took the measurements, ordered me one and I just got it today. It fits! Not only that, the old seal was starting to wear a groove in the shaft, and this new seal is slightly off set so it will seal on a different section of the shaft by like a 1/16th of an inch... perfect. The seal was less that $6. I will be installing it tomorrow. By the way the NAPA part number is: Seal 4231

After bying a few diiferent rolls of gasket material to make new gaskets, I have like $25 bucks in to all of it. I will know if it all works in a week or two after I get it all back in the truck.

J

 

[gem1410]

Where is the oil pressure regulator located and how did you adjust it--thanks