1989 V6 Dakota. Starts and runs good, approx 148,000 miles. Fresh Mobil 1 and filter. No visible smoke from exhaust, (although has noticeable hydrocarbon smell) and no leaks. Uses a quart of oil in 300-400 miles. Any ideas??? Thanks

 

How's the MPG's?

 

Check your PCV valve.

Wash the motor off completely, and check to make sure you don't have a leak somewhere (I was leaking out the back side of the valve cover gaskets).

Past that, with those miles, you may just have worn rings; what's the compression like (i.e., run a full compression check).

Switch to a heavier oil; I'm running a 15W40 diesel rated oil in my 1988. (Yes, that's on the list in the factory service manual AND the owner's manual for the temps where I live, before anyone gives me grief like I do others )

RwP

 

What do hydrocarbons smell like?

 

I have had a few engines in the past that were almost as bad.... my 78 Plymouth Fury (still currently own) and 89 Diplomat (ex squad, no longer have that one) both with 318s, were a quart per 500-600 mile oil drinkers. In both instances, I replaced the valve guide seals (can be done without removing heads) which solved the issue. I have seen 1 other thing cause this besides leaks or being just plain worn out, but yours being an 89 won't have a plenum plate on the bottom of the intake....
I have seen valve guide seals split from brittleness but usually they appear intact when removed, though you will notice the replacements seem like "softer" rubber.....
a set of valve guide seals and a set of valve cover gaskets should be the only parts you will need to buy, you need access to an air compressor and a good compression tester along with a type of valve spring compressor that lets you pull the springs while heads are on the engine.
By "good" compression gauge, I mean one that comes apart with couplings like an air hose would have. the only ones I have seen like this are usually tool truck brands. You won't actually need the gauge itself.

your valve guides themselves could also be worn out, for that the heads would need to come off and taken to a machine shop, i'd try the new seals 1st.... pretty cheap and should be able to do the whole engine in a couple of hours.

1 more thing.... don't waste your money on Mobil 1 for that old of an engine.... conventional oil is fine and these days still plenty costly.....

 

MPG's good, mid 20's
truck smells like a combo of running rich and oil burning
haven't checked PCV valve, will do
Previous owner stated that compression was solid, approx 140. He also stated that the heads had a valve job and the crankshaft was replaced, (bad bearing making noise). This is a super clean convertible with no rust and new paint and top, (hope I can figure out the oil issue)
No leaks, checked valve covers, etc. No oil on garage floor
Any good oil additive I can try
Thanks everyone

 

do the spark plugs have ash deposits? what do they look like?

 

haven't checked plugs yet, checked PVC, it's free and no wetness, (oil running from hose). When the engine is rev'ed, only a hint of black smoke comes from exhaust