V10 oil burner

As my signature indicates, I have a ’95 2500 4x4 with the 488 V10 and a 5 speed manual transmission. I had been looking for a truck like this in good condition for some time, but the V10/manual combination seems to be very rare, at least in this part of the world. When I found this truck it was the first example I could find, but unfortunately the poor old thing is very rusty. It seemed to run and drive OK, so I bought it for the drive train with the intention of doing a power train swap if I could find a 2500 4x4 with a good body and frame but the wrong engine /transmission combination.

Anyway, I don’t drive the truck much, but turns out it, burns oil. A lot of oil. About 1 litre per 500 Km local driving, which is mostly town and country at max 80 Kph and lots of hills. It starts and runs fine, with one minor exception, which I will discuss later.
There are no undesirable engine noises.
It does not go through coolant, and there is no sign of coolant in the oil.
It burns a lot of fuel, about 8-10 MPG Imperial, but I expected that. It seems to have no shortage of power.
The spark plugs are all as grey as a badger’s tail with no noticeable difference between plugs.
The engine is dirty with evidences of oil leaks just about everywhere, but there are no drips on the pavement when parked and no wet indications on the undercarriage.
It does not smoke on start up, or under steady load or acceleration, but it does smoke on deceleration. If you are going down a long steep grade, it will smoke enough to do a WW2 convoy escort laying a smoke screen proud.

I did some tests to see if I could find out where the problem is. The tests were performed at sea level +~300 ft.
Just to determine if the bottom end was OK I installed a known accurate oil pressure gauge and checked pressures at operating temperature. They were within factory spec at ~ 20 PSI @ 500 RPM, 30 PSI @ 750 RPM, and 53 PSI @ 3000 RPM (10w30 oil).

Manifold vacuum at 750 RPM is 19.5 In Hg. At 3000 RPM no load it is 23.5 In Hg

Compression spec is between 170 and 190 PSI. Here are the results, engine warm:
#1 - 179 PSI
#3 - 172 PSI
#5 - 179 PSI
#7 - 175 PSI
#9 - 175 PSI
#2 - 170 PSI
#4 - 177 PSI
#6 - 173 PSI
#8 - 171 PSI
#10 - 169 PSI

I also did a cylinder leak down test with my DIY leak down tester. 2 gauge with a 0.040” orifice. Using 80 PSI reference pressure. Most of the leakage was heard from the open oil filler on the right rocker cover. I did not hear any leakage at the tail pipe, I did hear some leakage at the throttle body, but thinking about it later, this may have been from the crankcase vent orifice as I neglected to disconnect that from the intake manifold. Here are the results, engine warm:
#1 – 5%
#3 – 20%
#5 – 1.25%
#7 – 7.5%
#9 – 13.75%
#2 – 5%
#4 – 20%
#6 – 27.5%
#8 – 10%
#10 – 3.75%

These results aren’t great, but I don’t think they are bad enough to justify the quantity of oil use. I suspect it is a combination of worn rings and worn valve guides with hard seals, but again, that is a lot of oil to be going through.

The other minor problem I mentioned is that when warm, the idle will surge.
When first started it will idle at ~850 RPM as smooth as a kitten, but as it warms up, and the idle speed drops, it suddenly starts to surge a bit. It idles at ~ 750 RPM and ~14.7 AFR. It will gradually lose revs and the AFR will increase to ~ 16.5 and it will start to miss, at which time a correction is made and the speed increases back to ~750 RPM and ~14.7 AFR with a smooth idle. The cycle takes about 10 seconds. It is not throwing any codes.

All of this has me puzzled, and I sure would appreciate some opinions.

Thanks.

I don't think that I can be much help just because I'm not very familiar with the V10s.

You say that the engine smokes during deceleration. Engine vacuum is usually strongest during deceleration because the RPMs are much higher than idle due to rotating momentum but it is still being fed from the idle air control valve only. As such, the engine will suck the manifold dry very quickly and thoroughly which will in turn create a strong vacuum. If oil consumption is the result of oil being sucked into the intake manifold, the problem will be made worse with stronger vacuum as the vacuum will draw even more oil into the manifold which results in more oil available to get pulled into cylinders and burned off.

However, although this theory could apply to the V6 and V8 engines with the two-piece intake manifolds with toasted plenum gaskets, I'm not sure how well it would apply to the V10 engine as they used an entirely different intake manifold design altogether. I have no idea how prone they are to taking in oil.

Food for thought anyway. And of course, it's just a theory.

It definitely pulls a lot of vacuum on decel so oil is entering the combustion chamber some how. I just don't know exactly where. It's also odd that all plugs are nice and grey with no sign of oil fouling, yet it uses a LOT of oil.

Could it be just like the 360 where the plenum gasket leaks and basically becomes an oil disposal?

Thanks, but the V10 has a single piece lower manifold, unlike the 360. That's not to say there couldn't be flaw in the casting, or a gasket leak, but nothing shows up on any particular cylinder.

Check your valve seals, or just replace them. Its a common problems in diesels that have throttle plates (Some do have them before the turbo to help with low noise engine braking, its just not common) where the intake side is under high vacuum and pulls oil through worn or damaged valve seals. I'm not sure what the effect smoke wise would be on a gas engine, but it sure does smoke on a diesel.

Another possibility is a bad PCV valve that is stuck open. That would cause large amounts of crankcase vapor to be pulled into the intake under high vacuum of deceleration.

You can test that by simply unplugging the PCV valve from the valve cover. If it stops smoking I would replace that valve.

There aren't many other things I can think of off the top of my head. The gas engines don't have oil spray onto the underside of the pistons to get sucked up. If it was a head gasket, there would be other problems related to that.

I would bet on either the valve stem seals or the PCV valve. The PCV valve is gonna be the more likely of the two.

+1 to checking pcv and crank vent system.

I suspect that the valve stem seals could be a contributing factor, but it does not smoke on start up, which is an indication of bad seals.
As for the PCV, it doesn't have one. Instead, the V10 uses a fixed orifice fitting in the hose from the crankcase to the intake manifold so there is nothing to break. The only thing it could do would be to plug up and then there would be no way that the oil could be drawn into the intake manifold that way.

You described breather elbow. Should have both crank vent and breather elbow. Should look similar to this but may be black

I guess the PCV valve and breather changed sides depending on the year, at least on the V8's. But if you have just a straight hose going from the valve cover to the intake manifold after the throttle body, no wonder. There is a straight hose, but that connects after the air filter but before the throttle body. Only the PCV valve hooks into the intake manifold.

Pcv system, intake manifold gaskets valve guide seals. I would guess the rings are fine as the compression is good