[89mkiii]

Yeah I add about a quart or so every other day...not so much the distance but more more so basically if I drive hard. The car spits out the oil (black smoke) out the exhaust - at least I'm assuming it's oil.

Ok I know I have a mkiii BUT its not a BHG (Blown head gasket) - smoke isn't white and my friends say that I'd know if the head gasket was blown.

What I do know on my 1989 supra NA manual:
Compression check shows 5th cylinder is slightly bad (15-20 lbs?)
PCV valve probably needs to be replaced - lines running to intake manifold might be clogged as well - adding an oil catch to fix that.
Valve gaskets may have been improperly installed or may need to be replaced.
Oil pressure gauge in car reads really low when idling/low rpm
Car does run better (less smoke more power) with chevron gas vs shell or 76
Plugs need changing ( I get paid on thursday!!!)
Could it be the oil sending unit? I read this from another post:

This is the Oil Pressure sending unit. Typically it can leak if not properly tightened, but there is no gasket. The cam position sensor is higher up and further right, but often the rubber ring sealing it can leak and drip down to the Oil Pressure. Also, valve cover gaskets could cause a leak in the similiar area. I suggest you make sure that the sensor is properly tightened, then check the other two possibiliites.

BTW yes there is oil around the oil sending unit and around the rear of the engine near the valve gaskets. Derr, oil is probably leaking from those places but I can't say for sure because the engine was pretty dirty all over when I got it. If I were smart I'd clean the engine and then look for leaks aha!

I'm thinking that I might have a couple different issues here and some symptoms might not necessarily be for certain problems...help.

I'm new to toyota nation so haven't done a good search for this problem on the site but I did see a lot of good advice on other postings. Hoping someone can help me diagnose. I don't mind chaning the parts as long as the problem gets fixed!

 

[Jeeves]

You're consuming a quart of oil every other day!? That's insane. No amount of hard driving should cause you to go through that. Especially not in an N/A.

Compression check shows 5th cylinder is slightly bad (15-20 lbs?)

That's not slightly bad. Slightly bad would be 100psi. That's downright horrible.

Oil pressure gauge in car reads really low when idling/low rpm

Common issue with Supras, not to worry about.

Here's the issue. You can leak all you want from the valve cover seals, oil pressure sending unit, and cam position sensor but to use a quart every other day is down right horrid. I'd quit driving it asap, if you keep driving you're just going to downright need a new motor. As you don't have turbo seals to worry about, my guess right now is that you've popped the headgasket around number 5 and the oil passage is leaking into the cylinder and being burnt.

A good leakdown test may be in order to tell you where pressure is going in Cyl. #5.

 

[89mkiii]

"Slightly bad"

Clarification:

MY BAD...
When I said the 5th cylinder was slightly bad at 15-20 I meant that if the pressure was normal at (for example) 150 lbs then the reading that I was getting was about 130 - It's been a while since I did the compression test so all I remember was that all the cylinders were normal except for the 5th one, which again was 15-20 lbs below the norm.
I think I'd notice something if I only had 15-20 lbs of pressure in the 5th cylinder!!! "Um, yeah that off/misfiring engine sound is the sound of my um, racing cam."

Forgot to mention:
After I change the oil I swear the oil turns black from its "golden" color pretty quickly. Normal?
ALSO...is it a coincidence that the bad 5th cylinder lies directly underneath the PCV valve?

Maybe the quart of oil every other day was a slightly exaggerated but yes it does consume more oil than it should.
I'm changing the plugs and adding an oil catch (hope it helps just a little and I know it's not too necessary for NAs) this Sat. I'll change the PCV valve while I'm at it.

 

[toyotafan]

well first ..... you would have blue smoke if you were burning oil.... common enough among small engines ........ my friends suzuki burns 2-3 quarts a week and its blue smoke ...... the black smoke is carbon ....... you are running rich ...or maybe your plugs are fouled .....did you check under the car for blow by? if its a rear seal you would not even see it except for the blow by under the car........ front seal is easier to tell along with all other common blow by areas ...... the black smoke is bad because if the engine is carbon fouled you could have carbon build up on the valves and pistons and i beleive your engine is an interferance type engine so too much carbon built up could lead to a blown piston. if your pcv valve is plugged to the point of being the sole culprit in your oil consumption then your problems run deaper than a pcv valve ........ you will need to replace all the gaskets ....... and it is possible to have a blown head gasket with having a missing cylinder ....... you could be shoving compression back through the radiator and the engine still run flat out and fine...... if you drive as hard as you say then this might be the problem ..... this is very common among I6 and small block V8s..... check the radiator and see if you have oil in your water .... the oil turning black right away worries me some and ties to the engine running rich ..... sounds like you need new rings because thats gas blowing by the rings ........ my advise is to do some more trouble shooting ....
if all other cylinders are with in 25% of each other on compression and 1 hole is low ..... strip the head off and replace the gasket and check the head and block deck for warpage...... or replace/over haul the engine. the point is .... on a precision motor .. don't go for the quick fix ..... do it right .... head gasket is cheap enough ..... start with the plugs and move to head gasket

 

[toyotafan]

isn't that a 7M-GE in an 89????? if so i just came across 1 for 750 dollars down in your area ..... infact I have a 7M-GE that I am not sure what I am going to do with because I am upgrading to 7M-GTE or maybe doing the twin turbo V8 swap .......

 

[89mkiii]

lotta info there...

Ok in response to toyotafans reply:
(thanks btw)

-1st off, engine swap would fix it all. engine prices aren't too bad but money and time are the issues; if I can fix what I have then I'll go that route. Otherwise I'd be planning on swapping and rebuilding the old engine, yay.

-Just changed plugs. They were definitely worn well - turning white in color. Talk about power increase! Should've changed them like, 10k miles ago
Still need to change wires.

-No oil in the coolant.

-My car smoke is black. Pretty sure it's oil. That and the oil loss is pretty proportional to the smoking that occurs. You say it's carbon fouled - I wouldn't know.

Head was resurfaced a couple years back and I was told the head gasket was changed...correctly I hope...so that's ok FOR NOW. Hope the head is still in good shape...it's run a little hot a couple times (Coolant is good! New coolant hoses are GOOD!)

*One important thing I noticed...
I was smart enough (finally) to rev the engine hard from the engine bay. Noticed a hissing sound - No not the sound of a blow-off valve...I have a NA! Sound appears to be coming from around the rear of the engine (5th cylinder area). Oil does appear to be leaking from there as well.

-Dealer told me that the 89mkiii has no PCV valves and they sounded pretty sure about it. Double checked the chiltons (says to check the PCV valve IF you have them) and dealer manual (whihc shows PCV hosing but no valves). Am I tripping?

-In any case I need to make sure that the hoses are clear - will be adding an oil catch and will replace hoses with steel braided or whatever is appropriate. They looked clear enough when I checked them.

Need to clean the exterior of the engine as well as the engine bay so I can clearly see what's going on.

So it looks like I'll be doing a valve job and replacing the valve cover gaskets. Might as well clean out the throttle body too. Sounds like fun.

That's cheap enough for me for now - slowly but surely and correctly.

Thanks again.

BTW what does blow-by look like exactly? Clear and kinda oily?

 

[89mkiii]

BTW

BTW I got the car used. I was told this and that were changed but who knows how well the work was done. Engine bay was pretty dirty as it was and little things were missing here and there.

 

[toyotafan]

blow by just looks like oil thats been blown all over the engine bay, its also caused by many oil leaks. but you can tell wich seals are leaking by the point at wich you start seeing oil covered parts.
example: if it leaks at the timing cover or front of the oil pan then the whole front of the engine is covered.

*One important thing I noticed...
I was smart enough (finally) to rev the engine hard from the engine bay. Noticed a hissing sound - No not the sound of a blow-off valve...I have a NA! Sound appears to be coming from around the rear of the engine (5th cylinder area). Oil does appear to be leaking from there as well.

is that the same cyl. with low compression .......
if it is ... take the head off and check for warpage on the head and block...... but it sounds like the gasket is gone.

 

[89mkiii]

blow-by/oil leak

Yes the area where the blow-by/oil is leaking from lines up pretty much directly with the 5th cylinder, near the rear of the engine.
The leak also lines up right where the dual pcv hoses enter the valve cover.

*This leak was coming from the valve cover gasket level. Not the head gasket level.


I would have noticed that the blow-by was coming from that area sooner had I cleaned the engine.

 

[toyotafan]

dude .... your low compression on that cylinder ..... hissing sound at the cylinder ...... there is no air being pushed in the valve cover to cause it ...... tht hissing sound means you are shoving compression through the #5 cylinder ..... thats either the plug isn't tight enough, or the wall is cracked at the plug, or the head and or block is warped or the gasket is blown. my 280Z was doing the same thing on cylinder #3 and it took me 3 months to figure out getting the head off would solve the problem. in my case the block was warped ... and head surfacing doesn't mean they checked for warpage ... that just means the gasket suraface was cleaned by mechanical means (I.E. sanding) and not chemically. now you probably do have a leek in the valve cover .... all cars leak oil from the valve cover. check the #5 plug again to make sure its tight with out over tightening. clean the area really good .... clean the whole engine really good ...... and check ..... but i bet that gasket is gone or you didn't get the plug tight enough

 

[89mkiii]

Interesting. I will check that 5th cylinder plug...
it was funny going in ( I just changed the plugs).

I know I didn't strip the threads...I may have overtightened it though...

Won't know til next...monday? Won't have time to do it til then.

I'll clean the engine too.

Not driving her for now.