Oil Consumption Mystery

[perryg114]

I have a 91 Eclipse GS-Turbo with 120k on the clock. I have always had problems with high oil consumption on long trips although short trip oil consumption is minimal. I at one time thought the turbo seals were bad and the extended running at highway speeds at partial manifold vacuum was sucking oil past the seals. I have seen alot of oil residue in the intake down stream of the turbo and also in the turbo intake. I recently rebuilt the turbo and found no problems with it. I have run Mobil 1 15W-50 oil (old red top formula) since the car was new.

So after the rebuild, I put in a fresh batch of oil and ran it 1000 miles back and forth to work (25 miles each way). I checked the oil level and it was just barely below the full mark. I went on a 350 mile trip, 175 miles each way. When I got home I checked the oil with the car cold and it was a quart low. The car has always been well maintained and I would think if I had valve seal or ring problems that it would burn oil all the time not just on a long trip. The car runs well and does not smoke. I also replaced the PCV valve and the old one was fine.

I am thinking and hoping it is something that can be cured with a catch can or something like that. The turbo pressurizes the intake at random intervals so that has got to reek havoc on the PCV vent system that really wants a constant vacuum not 11 psi then vacuum back and forth. All the hoses are stock an intact.

It was a very hot day 100 F and I was running the car about 80 MPH. Could the oil just be evaporating from the heat?

Perry

 

[JAG]

I think you should get a used oil analysis and see how much fuel dilution there is. My first guess is that there is some. This has a huge effect on oil consumption when the oil gets hot, like it does on your long trips.

 

[perryg114]

Yeah I was thinking of getting an oil analysis. I have been using Blackstone on my truck. Are there any good alternatives to Blackstone? I guess if I had alot of blowby problems it would show up on the UOA. If fuel dilution a big problem with fuel injected engines?

Perry

 

[JAG]

You could use Terry Dyson for analysis or ??.
Your engine could have fuel dilution from one or more of the many little parts that make a modern engine work right.
Spark plugs and wires, whatever gives the "juice" to your plugs, injector cleanliness, 02 sensor, MAF sensor, etc.
It's tough to keep an older modern engine running like new. All these parts degrade and when they do, the engine suffers from it.

 

[Curious Kid]

Not that I do this everyday, I'm wondering just how much combustion pressure is getting past the rings, leading to more uptake for the PCV system, which will take oil mist with it. I imagine that the turbo is enabling higher cylinder pressure than any NA engine would see, and thus at greater risk of such issue(s).

Just a thought/opinion mind you.

Take care and good luck with finding the cause.

 

[perryg114]

Well there is that issue of more compression and more blowby but there is also the issue of how the PCV system works while the intake is at positive pressure. I think the problem is happening when I am not at boost on the flat and level.

 

[Bobert]

I used to have a 90 GSX and the consumption is fairly high in that motor (especially with M1). My friend had a 91 Talon and his consumption was just as bad. Give Rotella T Synthetic 5w-40 a shot or if you want a 50wt. oil try Castrol 5w-50. Both these oils should reduce consumption.

 

[perryg114]

I never tried a different oil in the car. I may have to do that. I run Mobil 1 10w30 in my 95 Ranger and it does not burn hardly any oil in 10,000 miles. I would like to go thinner in the Eclipse but since it is already burning the 15W-50 I did not attempt it. The lifters might like the lower viscosity but lower viscosity means lower oil pressure at idle and the Eclipse only has about 10psi at idle so it is no wonder there is some lifter noise. I am getting off subject here. The higher oil consumption on long trips means something I just don't know what.

Perry

 

[Mokanic]

The engine blocks in the late 80s -early 90s Eclipse as well as non-turbo Galants were very soft. By soft I mean after 100K the cylinders suffered greatly from wear and being egg-shaped. I have bored many to stop consumption problems. The iron found in the 3.0 truck/van engines was alot more wear-resistant and had it not been for valve guide problems it would have easily been a 400K engine.

 

[Bobert]

Quote:

---

The higher oil consumption on long trips means something I just don't know what.

Perry

---

Higher consumption during high speed highway driving is perfectly normal in many motors. In fact my VW owners manual makes a specific mention that oil consumption during high speed driving is normal.

My GSX used to drink oil on long trips too.

 

[perryg114]

Maybe it is something I will just have to live with for now. I may change oil brands and see if that helps. I will do a compression and leak down test when I get a chance.

Perry

 

[Bamaro]

That engine is known for having bad valve seals. I had a 90 Laser RS (non turbo)that would use a lot of oil, started around 80 or 90K. After idling for awhile, I would see a puff of blue smoke come out when I started up. The longer the idle, the more smoke.

 

[perryg114]

It was the valve seals and it almost ruined my engine. There was so much carbon that is was eating my valves and seats. I found this out after changing a timing belt. I have knocked some carbon off the pistons and the carbon jammed the valves open. I thought I have bent a valve but it turned out I just knocked some carbon loose and it held the valves open enough so it would not run. It was a good thing because it would have ruined the engine if it had gone on much longer. I replaced the exhaust valves with stainless steel ones and lapped the seats back into shape. The margins were a little wide but otherwise ok. The car runs great now and does not burn oil.

Perry

 

[mechtech2]

See... nothing to it!







JK - nice work!

 

[perryg114]

It was not fun work though pulling that head.

Perry