I have noticed while idling, my 88 Dakota 3.9 V6 is smoking some. After I drive it for about 15 to 30 minutes, I check the oil level & it is fine. I have noticed while idling, the oil pressure gauge registers kinda to the low side but while driving, the oil pressure gauge registers in the middle of the gauge.
Faulty gauge, faulty oil pressure sensor, or is this normal?

Thanks for the info!

 

That's normal, oil pressure increases with RPM. That said, I don't think the gauge is so accurate either.

​​​​​​If your oil pressure light comes on, that's when you need to worry. And not worry as in, "I'll get that fixed soon" Worry as in, park it until it's fixed else prepare to grenade the motor. But sounds like that's not your situation.

Black smoke? Any other symptoms?

 

The color and odor of the smoke may be significant.

However - at this age, the valve seals are almost guaranteed to be leaking (which will cause a big puff on start, and may smoke some all the time); the TBI sucks for idle management compared to MPFI/SEFI (it's actually in the FSM that a pop of the throttle WILL yield a blast of black smoke out the tail pipe due to how poorly TBI designs handle the sudden change in load); you may also be sucking some coolant; and last but not least, at this age, it may be getting some blow by so check the PCV valve and the crankcase air breather (PCV valve - here's a conundrum. If I use the Mopar valve, my oil consumption is down, but I lost a front seal within two months; with the Fram PCV valve, oil consumption is almost triple, but at least I'm not losing seals. Both are due to the excessive blowby of right at, as I type this, 370,000 miles of over half of it neglect on the part of previous owners ... YMMV natch.)

As to the gauge - as Tbugden pointed out, that's normal. And think about it; pump runs slower at idle, it won't pump as well. General rule of thumb is 10psi/1,000 RPM as a minimum, so if you're really concerned, pull the oil pressure sending unit, put a mechanical gauge on, and see what you have. Shucks, I'm considering, when I rebuild, to put a "T" in and put the mechanical gauge under the hood so I can check when working on the truck; otherwise, it's not that big a deal ("Over my panic level at idle, under the high panic at cruise? Good! Exact pressure? Who really cares??" *grins*)

RwP

 

Thanks for the info Tbugden & RalphP! I have changed the PCV valve(NAPA part# CRB 2-9207) and the crankcase air breather(NAPA part# FIL 2997). It smokes a little white smoke first thing in the morning & when idling, just a little bit of white smoke.

 

White smoke is moisture/water. It may just be condensation, or, it may be coolant. Losing any coolant?

 

Also, what's your humidity? It may just be the natural byproduct until the exhaust system heats up enough.

Plus ... how old is your cat? If it's failed, you'll get more water vapor because it won't fire up and heat the exhaust up enough to boil the water ...

RwP

 

Not loosing any coolant. The humidity here is like 90 to 100% this summer. The cat is probably original. I am the 3rd owner of this truck. I bought it last October.

 

Since you're not only sucking water vapor in, but a "perfect" hydrocarbon combustion yields H2O and CO2 (Water and Carbon Dioxide) as results, I'd expect water vapor on start.

Check the cat after five or so minutes; if the exit isn't hotter than the inlet, it's failed, and you're getting more water vapor out as visible vapor instead of as invisible steam due to that, until the rest of the system heats up enough to keep it all above the vapor point.

(If it's failed, it's up to you ; legally, you're supposed to replace it with an OEM unit; practically, you can bypass it with a pipe, rod out the current, or whatever you want to do - just be aware that by federal law, that's illegal. Up to the local law to prosecute, so ... )

RwP

 

Thanks RalphP! I will do some research here in the near future!