My oil pressure light comes on when my truck is roughly under 1k rpms. I bought a new sensor, but someone pointed out that with the manual gauge that the previous owner installed, I don't need a new pressure sending unit as the mechanical one will always be accurate.

Took his word for it and returned it. Checked the oil. I put 5 quarts in when I did the oil change about 10 days ago, and today it was bone dry. Put some leak fixer and another 5 quarts in today. Haven't seen any oil on the ground. I do have some white smoke puffing out the back. The guy at the part store put his hand on each of the tail pipes and said the valves should be fine (not sure how he determined that).

I drained some coolant, and no oil was in there. My buddy says it could be going through the heads or something - not exactly sure as I'm not savvy when it comes to vehicles. I'm starting to think maybe the oil isn't leaking, but burning, which is apparently a common issue when the plenum goes bad.

SO - if I have a bad plenum, should I stop driving until I get it fixed? I've got about 2 hours of driving to do tomorrow evening and I don't want to risk burning the motor out, cracking a head, or whatever.

ALSO - I called a few part stores, and nobody even carries plenums (at least for my vehicle). One guy suggested a scrap yard, and another suggested cleaning it with throttle body cleaner and perhaps getting a new gasket for it for about 12 bucks. He said that if I could find one, it would cost around $200, which I really don't have.

So, is she ok to drive for now?
Is there a place I can buy a plenum? I'll do some looking around to see if I can find out how to clean it, but beyond a simple oil change, my hands-on knowledge is pretty limited.

 

The plenum is an area in the intake manifold, not a part. You can do just the gasket, but who knows how long itll last. Read the plenum sticky at the top of the tech page.

As far as losing 5 quarts in 10 days, thats bad. Need to find out for sure where its going. White smoke fron exhaust is moisture (or coolant if smoke is bad enough). Blue smoke would be oil.

How many miles were driven in those 10 days?

 

I'd say about mayyybe 100, probably less.

It's really throwing me off, because it's not dripping anywhere.

 

As far as your trip tomorrow, as long as you keep oil in it and have oil pressure you should be ok. Just find out where its going asap.

 

Well, there's a new problem now. I drove maybe 5 miles tonight, and if I keep normal RPMs (basically, just not gunning it), when I hit about 40-45 mph, the whole truck starts shaking like it's in an earthquake. I have no clue what could be causing that. I've heard that alignment could cause that (and my alignment is not good at all). My tires are also cambering in the front. But I never had this issue until the last 48 hours when I replaced the temp sender, added a thermostat (there was none), heater core, and undid the heater core bypass. I just don't see how any of that could have caused this issue, but it was all that happened recently.

I'm seriously bummed out about buying this truck. I don't have wads of cash to throw at it, yet everyone insists that I got it for a steal at $1,500. Well, it's not running well, and I've already dropped around $400 more into it.

Can anyone help me out here? Things are feeling desperate!

(The other standing issue is my oil pressure sucks. Goes down to 0 when the RPMs go under 1k or so. Not sure if this is related.)

 

That is 1 qt every 20 miles, highest usage I've ever read on here. Another couple hours driving won't hurt at this point as kejobe stated. If it's sucking/burning that much oil then damage has most likely occurred. Clogged cat....excessive heat backup causing burnt valve s and 02 sensors probably shot. Piston and cylinder wall damage from constantly running out of oil. Have you pulled some plugs to see if oil fouled , especially #8 and#7? Oil pickup screen could be sludged up from low/no maintenance, resulting in light coming on. More info would help...mileage, how does it run overall...any check engine light codes. That speed is when OD is engaging and misfiring can be more pronounced then. More smart guys will chime in during morning hours as they are smart and in bed now.

I would be doing compression testing on engine to get an idea of overall health and to see if it's worth putting anymore money into it. New plugs , wires , cap and rotor would help if engine is ok. If run likes crap front 02 sensor prob shot and catalytic convertor is clogged. Is body in good condition?

 

When your friend said he thinks its burning oil, he was probably talking about through the piston rings. Your pistons have rings on them that slide against your cylinder walls and create a barrier between the oil below and the combustion chamber above. If your rings are worn or your cylinders damaged, (from the sounds of it, probably both), then you will have oil go into the combustion chamber (just below the heads but above the piston) and burn. With that much oil loss and no leaks, I would say you should see an impressive smoke show coming from your tailpipe. As mentioned above, it will come out a blue-white smoke. Sorry if I went into too much detail, I just wanted to explain where your oil is most likely going.

This may sound bad, but I think your most cost effective repair would be to find a replacement engine if the damage mentioned above is the case.