Extended highway speed = oil usage.

Messages
35
Location
Chico, TX
I have a '96 Miata which I've been trying to track down a problem. I got it with 124,000 miles on it, previous history largely unknown. I have a 120-mile a day commute, and it hadn't been using any oil between changes. 12 miles of said commute is at 70MPH, the rest is 60-65MPH. The problem started when I drove to Houston (from Dallas) and back. It was mostly at night, so the speed limit was 65MPH. The car used half a quart on these trips. I have a fuel filter in the PCV tract to catch and remove the oil vapor and normally there are just black specs on the filter, now there was an ounce or so of oil. There are no leaks that I can spot (checked everything but the rear main seal) and no visible smoke from the tailpipe. I have not performed a compression or leakdown test yet. The oil used is 10W-30 and now 5W-30 Mobil 1. Any ideas on this one? It has me baffled with only using oil during extended trips.
 
Messages
9,448
Location
USA
Use progressively heavier oils in it until it stops. I am betting that 10W30 or 15W50 M1 would reduce this or solve it. You did check the pcv and EGR circuits for proper functioning?
 
Messages
9,365
Location
USA
my g/f has a 96 sunfire with 2.2 Liter engine/102k miles. it does the same thing. oil consumption around town is negligible. when we take the car to go see her folks out of town, apprx 400 miles roundtrip. car uses 0.5 qt oil. I notice this oil consumption when she drives 80 mph or higher. at 80 mph, she's running at 3500 rpms. I think there's a connection.
 
Messages
1,533
Location
Ephraim
Does it burn oil only on these NIGHT trips? Is that what youre saying? Since you just got it, and it seems dry, may it be probable that you are using a better oil than the other owner, and it is cleaning and being used up by burining and pulling dirt from the engine?... if a better oil cleans the ring area, that can increase consumption, sometimes for a long while or forever... donno the condition of the internals. give it 5-10-15 K miles, always checking it and short OCI's until you find the problem or it goes away!
 
Messages
22,188
Location
Colorado Springs
Sometime adding the fuel filter inline with the PCV valve will increase vacuum substantially through the PCV line, which will suck more oil through the PCV especially when there is less vacuum in the intake manifold and the filter is all soked up with oil. Or, I guess it could completely clog perhaps and not allow proper PCV funcioning, but the fresh air side would then draw vacuum, a lot of vacuum when the engine is idling etc. or decelerating, when the PCV normally closes. That would suck up a lot of oil vapor. These are all guesses though [Cool]
 

Narcoleptic

Thread starter
Messages
35
Location
Chico, TX
quote:
Originally posted by JohnBrowning: Use progressively heavier oils in it until it stops. I am betting that 10W30 or 15W50 M1 would reduce this or solve it. You did check the pcv and EGR circuits for proper functioning?
I had beem using 10W30 Mobil 1 until winter. Mazda engines are famous for HLA noise I know, but there was extended HLA noise on cold starts with the 10W30. I switched to 5W30 and no HLA noise, even on cold startup. It used the same amount of oil even with the 10W30. I haven't checked the EGR yet, but I pulled the valve cover and resealed the PCV baffles in the cover. The Miata's 1.8L has three baffles in the cover sealed with RTV. It has a new OEM Mazda PCV valve. I plan to pull the intake manifold to clean it, as they have a reputation for carbon build-up jamming the EGR valve open and build-up from the PCV feed that can set a MIL if left too long. I cleaned the throttle body and got a good bit of gunk out of it.
quote:
Originally posted by Robbie Alexander: Does it burn oil only on these NIGHT trips? Is that what youre saying?
I added that detail because in Texas, the night speed limit can be lower than the daytime limit. For example, I take I-45 to Houston. Daytime limit is 70MPH, nighttime limit is 65MPH. I don't think it being day/night has anything to do with it.
quote:
Since you just got it, and it seems dry, may it be probable that you are using a better oil than the other owner, and it is cleaning and being used up by burining and pulling dirt from the engine?... if a better oil cleans the ring area, that can increase consumption, sometimes for a long while or forever...
These were my thoughts as well. I pulled off a Pennzoil filter when I got the car, and the only place I've seen use those filters were the quick lube (especially Jiffy Lube) places. I've already put 10,000 miles on it (currently at 137,000 miles, got it with 124,000) but will keep an eye on it. I've also been debating about trying Auto-RX.
quote:
Originally posted by Drew99GT: Sometime adding the fuel filter inline with the PCV valve will increase vacuum substantially through the PCV line, which will suck more oil through the PCV especially when there is less vacuum in the intake manifold and the filter is all soked up with oil. Or, I guess it could completely clog perhaps and not allow proper PCV funcioning, but the fresh air side would then draw vacuum, a lot of vacuum when the engine is idling etc. or decelerating, when the PCV normally closes. That would suck up a lot of oil vapor. These are all guesses though [Cool]
I had not of heard this. Its something I generally do because oil vapor lowers fuel octane, and as I said above the Mazda 1.8L in the Miata dusts the intake with oil vapor gumming up the throttle body and cause eventually set a MIL. Periodic removal and cleaning of the intake is the usual cure. Thanks for all the suggestions/ideas. The car runs great so I'm not too worried about it, and I buy the 5-quart jugs of Mobil 1 so the extra usage is covered between changes. I know that higher mileage engines may exhibit behavior like this, I just got spoiled by my '97 Pathfinder's engine using no oil between 5,000 mile changes with 126,000 miles on it. I also realize that the PCV setup in four-cylinder engines and/or high-revving engines tend to use oil more.
 
Messages
22,188
Location
Colorado Springs
If your fuel filter in your PCV line is getting quite a bit of build-up, you may want to just get a real honest to god catch can. That will solve pretty much all oil ingestion problems through the PCV, and depending on how you either make the can or which one you buy, you can still route it back into the intake manifold so you'll still have vacuum through the crankcase.
 
Messages
269
Location
High Up in the Rockies
Is their a PCV valve on this car? Is it working properly? The crankcase can be pressurized by too much blow-by and not enough ventilation. This will cause oil to be blown out the dipstick tube, seals, etc.... A plugged PCV valve can cause this. If your PCV valve is not closing under high load, it can suck on the crankcase too much and pull in oil. DEWFPO
 
Messages
43,650
Location
'Stralia
Drew, are you sure about that ? Most cars I've seen, if idling normally get pretty upset when you put your finger over the PCV opening
 
Messages
1,565
Location
palm beach
the miata has 2 valve cover vents. one for pcv, and the other is to draw in fresh air. under high load low vacuum conditions, the one which draws in air will somtimes reverse flow and push out oil vapour. adding a fuel filter to the pcv line is pointless, an urban legend bscisally. oil vapour wont be stopped by any fuel filter, you would need some sort of charcoal air scrubber or somthing for that. you would be better off installing a catch can and routing both valve cover lines to this catch can. remove the pcv decive from the valve cover as well. a piece of fuel line fits prefectly inside the rubber pcv gromet, and seals well. the miata valve cover is designed to trap and release as much oil droplets as possible, you have taken it apart already, im sure you seen the angled tubes with 45 degree cuts and indentations in the oil trips. its a clever design really.
 

Leo

Messages
911
Location
Australia
quote:
Originally posted by cryptokid: tadding a fuel filter to the pcv line is pointless, an urban legend bscisally. oil vapour wont be stopped by any fuel filter, you would need some sort of charcoal air scrubber or somthing for that.
Thats bullocks bro. I put one in, and it stopped a substantial amount of oil going into the intake manifold. How do I know? I checked the innards intake manifold before and 1000ks after I put it on. There was almost none in the intake manifold collector when before there was a heap. Altho now I've binned it and run a proper catch can system.
 
Messages
22,188
Location
Colorado Springs
quote:
Originally posted by Drew99GT: PCV valves OPEN under high load/low vacuum and close under high vacuum/no load.
Ok, they don't completely close at high vacuum/idle, but darn near.
 
Messages
39,806
Location
Pottstown, PA
quote:
the miata has 2 valve cover vents. one for pcv
Is it a true PCV ..or just a metered orfice? Big difference in function. The PCV is basically a regulated manifold leak ..open above a certain vacuum ..closed below a certain vacuum (at idle anyway). The CCV, however, is just a metered orfice that only allows so much flow to the intake below the throttle plate. This has been a Japanese signiture item ...venting excessive blowby gasses/vapors to the air cleaner.
quote:
adding a fuel filter to the pcv line is pointless, an urban legend bscisall
I don't know about a fuel filter ..but many an air compressor uses a filter/seperator to do just that ..remove oil/water from the flow. I like the exhaust drawn extractors. No fouling of anything ..totally passive and needs NO SERVICE.
 
Messages
39,806
Location
Pottstown, PA
quote:
Originally posted by Drew99GT: PCV valves OPEN under high load/low vacuum and close under high vacuum/no load. Ok, they don't completely close at high vacuum/idle, but darn near.
Okay ....AT IDLE the PCV valve is simply a self regulated manifold leak. It opens and closes as it bleeds engine vacuum. It will flutter constantly cycling. As it drops engine vacuum ..it closes (drops) ..as the vacuum recovers ..it opens (lifts). With very few exceptions this is a passive system that has operated this way since its inception. Some models, due to emission controls regulate this flow via electic solenoid (some jeeps that I'm aware of). While running (road speed), and the MASS intake volume is sufficient, it acts like a garden hose syphon ..operating in parallel to the carberator/throttle body. That is the higher the flow ..the more it draws into the intake. Both are outlets from the manifold plenumn point of "view".
 
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