88 D100 Oil Pressure issues...help/suggestions.
 

:confused:

I purchased this truck about a year ago. Came with a 318 that had 120K miles on it! I of course dove on it and have yet to regret the decision. However, as of late, I'm getting closer. There is an oil pressure issue I'd really like your all's help with.

The pressure is fine while at idle. However, it starts dropping as I accelerate unless I'm getting on it in which case it generally will go up somewhat. But even in this case, when I drop back down to coasting, or just maintaining speed, the pressure starts to drop again. Last weekend, we pulled the oil pan, replaced all the fluids, put a new filter on, cleaned the screen and the pump (which looked flawless) and put er' all back together. During the test 15 miles, its ran great. No problems what so ever. I want back to my buddy's house to clean up the mess we'd made. Made the 25 mile drive back to Maryville from Knoxville. Half way home, gauge started dropping again...doing the exact same thing. I haven't noticed any real difference in relation to temperature. I can't seem to find anyone with a gauge I can use for testing....but with it following the same pattern with the same actions...I don't imagine its a sending unit, or a gauge error.

My next move, unless someone can suggest other wise, is going to be to park and lift her for awhile and begin some exploratory surgery....which I fear will tell me I've got a cam bearing going...

All of that being said. If it turns out to be a cam bearing, I am going to up grade it to a cam from a 340. If I go with a stock 340 cam, what else will I need to look at upgrading?

Any suggestions on the oil pressure issue, or info on what else to upgrade with the cam would be greatly appreciated.

Try a windage tray?

Thanks for the reply. I should have specified.... It starts dropping off at below 20MPH....long before a windage tray should have much effect. Also, as I begin to come to a stop, from say, 55mph...as I slow down, it goes down even worse....until I come to an almost complete, or sometimes complete stand still...then it'll start to climb back up. It'll be dead center again by the time the light changes back to green, and will start to drop all over again as I climb back to 55...where it'll start to climb closer to normal range.

My 318 95 Ram w/ 240k does that. I changed the oilpump, same issue. Switched from 1-30 to 10-40, that helped some. When I had the pan off I should have plastigauged the rod and main bearings. A reliable source told me thats where I could lose alot of pressure. I also had a coolant leak into my oil which diluted it some, any foam in your, or on the dipstick? I seldom have heard anything about bad cam bearings, but anything can happen. Good luck.

Thanks scotts....nope. No coolant in the oil at all. I even checked for that when I did the oil change. The oil was dark (it was the scheduled 3K change) but aside from that....nothing. I have started to notice that it does get a little worse when it gets good and warm. Instead of climbing like it does if its cool, where it climbs around the 50-55 miles per hour area, it continues to fall, until its almost bottomed out and sit there...forcing me of course to drive really slow, or pull over and wait till it cools all the way back down to finish the drive home. This turns my 30 minute drive home into an hour and a half. A buddy of mine mentioned the main bearings as well....however, he mentioned that under normal circumstances if its the main bearings, you should start hearing that lovely clicking noise....of which, I have not heard hide nor hair.

In other news, I have noticed that when the pressure gets real low, its starts feeling noticeably rougher. That's my sign to pull over and sit for a bit.... so I'm pretty well convinced that this is not a sending unit/gauge issue.

Well now you know its probably an internal engine issue. Might as well band-aid it till you can do something about it. Thicker oil. Make sure your oil isnt being diluted either by gas from blowby, or even a bad fuel pump. That will thin it out.

Thanks again scotts. Now I'm torn. My local pull-a-part seems to be calling out to me "just replace it with a 360....you know you want too!!!". I'll keep you guys posted on what I figure out, and what direction I decide to take. In the mean time, feel free to brain storm on any other thoughts. I'll continue checking in case someone else pops up that's had the same problem.

Craigslist is a great place for motors. But yeah, do your homework before writing off the motor.