Mystery Oil Leak

[DeeZX]

There been an oil leak plaguing me for the past few months on my 1990 300ZX TT. It leaks on the right side of the front of the engine. It drips onto the pivot bolt of the alternator I changed the cam seals at least twice. and re-sealed the exhaust valve covers and replaced the intake vale cover rubber seals. I also installed a brand new oil pump-which came with a crankshaft oil seal.

I've search all the other post but could not find a definitive answer.

I have a few theories

-I think it might be the oil filter tree, but not sure if the oil would travel from there to the front.
-I also think it might be the oil cooler feed and return lines. The hose coming off the oil filter tree might have a hole near the alternator and the high pressure causes the oil to squirt out an spry on the alternator.
-I my not have done a good job when I was sealing the exhaust cam cover on that particular side and now it's leaking. <- I'll be pulling the plenum tomorrow to change PCV valves and PCV hoses I'll check this then.

You guys tell me what you think. Here are some pictures. Your help would be greatly appreciated.

[labcoatmonkey]

Is it alot of oil in a short period of time? Check the oil pan and make sure there arent any cracks in the block, or the headgasket isnt leaky. Its highly unlikely but has happened before.

[Re037]

try some uv dye + black light. they have it at autozone with all the ac refill stuff. its a small yellow bottle thats just dye, can be used in engine oil ac systmes etc.

[DeeZX]

Is it alot of oil in a short period of time? Check the oil pan and make sure there arent any cracks in the block, or the headgasket isnt leaky. Its highly unlikely but has happened before.

It's doesn't leak that much. It isn't pouring out. it drips slowly. probably about 3 to 4 drops of oil on the ground in the morning when I pull out the driveway. I'll have to give the block and oil pan a once over when I take the engine out again, which won't be for the next few months. I doubt it but, really hope it's not a crack block/ head, there is no coolant in the oil and vice-versa .

-It might even be a poorly torqued oil pump.

[DeeZX]

try some uv dye + black light. they have it at autozone with all the ac refill stuff. its a small yellow bottle thats just dye, can be used in engine oil ac systmes etc.

I'll try this
-thanks

[DeeZX]

I think I found it... Looking at the first picture, if you look at the lower of what I think is called the Plug-Thread or Cylinder Head Core Plug, there is oil soaked at the bottom half of the plug as if the oil has been leaking out from there. I tried to tighten it and then tried take it out to examine the thread, but it won't budge. The plug above it was like a half turn out, so I tightened it.

Are these known to leak? How do you change them? when you replace them, do you put Teflon tape on them or rtv or something else on them?

[MikeCTTZ]

Sorry to dig up an old post, but I have been chasing what sounds EXACTLY like this leak for a few years now. Just put new injectors, coolant lines, PCV and air control hoses on in June, along with valve cover gaskets, hoping one of the above might solve the problem. No dice. Pulled the oil cooler lines Monday and they are fine. To the original poster... did it turn out to be those plugs? I'm getting tired of fixing stuff that doesn't fix the leak.

Leak seems to come, as stated, from the passenger side front of the engine, below the valve covers, but above the oil cooler lines.

[t.mcginley.jr]

If it was your valve cover gaskets, your heads would be coated in oil too. Those head plugs and also freeze plugs can leak over time from heat cycling/age. If you can get those head plugs out you can put them back in with some RTV on the threads

[MikeCTTZ]

Thanks! I have had the car for 13yrs and was told by the local Z guru not long after I got it that the leak was the valve cover gaskets. I figured while I had the entire top of the engine off replacing the injectors early this summer (after finding a dead miss when I fired it up in May) I'd put new ones on it. I knew when I got them off they weren't leaking, or certainly weren't leaking bad enough to be what I was seeing. BTW, there's absolutely NO way to see the heads on a TT without removing the intake plenum, lol. That's why it is all guesswork. I have tracked everything I can see without taking major components off. Figured with the location and the quantity it might be a pinhole in the cooler lines, but having them off and looking them over, I'm pretty sure they are intact, as well. IDon't think it's the front seal, as the timing belt is nice and clean and it's only coming from the pax side, instead of center.

Guess I'll go ahead and pull the front end off the engine to get a look at those plugs. Guess I'll put ANOTHER timing belt on it while I am in there (stupid to put the old one back on when you are there, anyway). I guess I'll just pull an early 60K on it. I did an emergency 60K with only 12,000 miles on the last one because the last guys that serviced it right before I bought it didn't replace the idler pulleys at 120K (again, you are in there, anyway...). Top center idler started squalling, so I got my introduction to replacing the timing belt and all that in the first two months of ownership. Pulled a full 60K and replaced all idlers at that time. Won't hurt to put new bypass hoses on the water pump, anyway. Not many miles on them, but they are 13yrs old.

[t.mcginley.jr]

Have the idler studs ever been replaced? They are not technically a maintenance item but they do occasionally break with age/higher miles. They are hard to replace once your in there.

EDIT: They aren't hard to replace once you're in there.

[MikeCTTZ]

I doubt the idler studs have been replaced. I put all new idlers on it, but didn't know the studs were an issue. Wonder if they break spontaneously, or if noisy idlers go unnoticed/attended until the bearing seizes and wrings a stud off?

Went out and looked again, just now. There's oil below the head, but well above the oil pan. You can only see a little of the head under the vallve cover, but it is clean up that high. Alternator and PS bracket and tensioner is dripping in oil. AC compressor and tensioner on the other side is perfectly clean. Slight bit of oil on the water pump, but probably just getting blown around under there. I'm leaning towards those blanking plugs. Wish the OP was still around to say whether the plugs were his problem.

[t.mcginley.jr]

If its a valve cover gasket, oil usually leaks down over everthing depending on where its leaking from. I don't think I've ever heard of those plugs leaking on any car really. Are you talking about the threaded plug with the hex shape, or the blank freeze plugs that look like this:

[MikeCTTZ]

From the pics and description of the OP, it is the threaded hex head plugs. The driven in stamped plugs like in your pic are usually in the water jacket (BTW, they are not "freeze" plugs and will not keep the engine block from cracking if ice forms, they plug the holes left by the casting mold core supports). If it was a coolant leak, I'd sure suspect those, but have never seen that type plug used on an oil system. Probably too great a danger in it blowing out due to high oil pressure when cold.

Here's a quote from the post immediately before my first post...

"I think I found it... Looking at the first picture, if you look at the lower of what I think is called the Plug-Thread or Cylinder Head Core Plug, there is oil soaked at the bottom half of the plug as if the oil has been leaking out from there. I tried to tighten it and then tried take it out to examine the thread, but it won't budge. The plug above it was like a half turn out, so I tightened it."

Note in the very first post f the thread that his leak was on a 1990 Twin Turbo. Exact same car as mine and both are early production runs. Could have been a missed point in the assembly line that wasn't caught until later. Just sucks to have to dig down that far to see, which is why it would be nice to talk to the OP.

[nismo300zx1990]

Mike i to believe my hex plug on my right side head is leaking. When i have the motor running i see oil coming from there and it i a good size amount.

[MikeCTTZ]

Interesting, another 90 model, too... Thanks. I will indeed report back when I dig down and see if that's it. Probably get into it tonight or tomorrow.

[t.mcginley.jr]

What tool did you try to loosen the hex plug with? They look huge

As far as those "freeze plugs", it's just my habit of calling them that from rebuilding old small block fords/chevys. And they do use smaller version of those plugs on these engines in specific locations. For example, on the TT block they put two small plugs in the block wall where the oil filter tree mounts. On the NA block, they put the check ball valves there, but on a TT the check ball valves are in the oil filter tree itself. They are usually tapered so once they're in the only way to get them out is a hammer.

[MikeCTTZ]

OP was the one that has been in there. I have not even seen these plugs yet. About to go out and tear into it. I have a set of 3/8 and 1/2" drive allens that go up to I think 24mm. If they are bigger than that, I have a full machine shop here at the house, so I'll make whatever it takes to get them out, if they are indeed the problem. My greatest fear is getting down to them and finding them bone dry, though. Guess no matter what, i might get down to where I can see the leak, even if that's not it.

From the pics above, it sure looks to be the exact location the leak is coming from, though. I have been fighting through a few leaks. Had a split in the PS return line that had that whole side soaked down and got that fixed. Figured it was the valve covers, so I did them. Pulled the oil cooler lines last week, so I am narrowing it down, if nothing else.

Didn't know they used those "freeze" plugs in those locations. I have replaced plenty of freeze plugs over the years. Had a 1970 Mercury with a 429 that had a thin casting in the plug right over the starter. If you ran it hard, that plug would indeed blow out and dump the coolant on the starter. You got to replace both the plug and the starter.

Anyhow, I'll report back later this evening on what I find and thanks again for your insights.

[MikeCTTZ]

OK, it's the VVT pulley seal. When I got the VVT pulley off, there was a visible trail coming from the seal area and running down the inside of the engine-side metal timing belt cover. Same on the back side of this timing belt cover, with a trail running down to the lip at the bottom. You can see fresh oil on the head from the boss where the intake cam comes out, all the way down onto the block and all over everything. All around the fringes is caked with oil soaked dust.

I got a real good look at my valve cover replacement job with the metal timing cover off, and I'm proud to say there's not even a damp spot (whew!). The exhaust valve cover seals really had me concerned, as there is simply no way to check that on the exhausts side (even with a mirror) and it's a gray RTV seal, not a rubber gasket like the intakes. You just have to hope you don't drag your RTV bead across the exhaust valve parts getting it in there.

Solved the mystery of why oil everywhere else, but not on the timing belt or in the outer timing covers. The back side of the pulley, where the oil was slinging off, lies EXACTLY on the plane of the thin metal engine-side timing cover. There is a plastic grommet in the cover that surrounds the hole where the pulley comes through. The oil slings off the pulley and hits this grommet instead of flying all over the timing belt, then it runs down the surface of the cover and drips off at the bottom... on the pax side front of the engine. The grommet on my car is broken in a few places, so that's how the oil ended up on both sides of the metal timing cover and all over the head and block.

Seal is a double lip type, with inner sealing lip and outer dust shield lip. Both seal lips were in contact. Won't know until I get the seal out if the inner lip was shredded or just got loose over time. I do know my PCV valves were hung up and probably blowing boost into the crankcase (found that on the injector swap when I replaced everything I could get my hands on under the plenum). Lip seals are usually only good for 10PSI or less, so that seal may have been the weak spot that gave out. Seal surface on the pulley still looks nice and shiny, without grooving, so I'll just give it a quick polish on the lathe and let it ride. I figure I'll use the small sheet metal screw and pliers trick to get the seal out without risking gouging up the cam nose with a seal puller.

I did go ahead and check the hex plugs while I was that far in. They are both solid. They were covered in oil, but it was from the oil running onto them from the seal failure. BTW, they are 17mm for future reference. From the time on my last post to this one, looks like it took me about 3hrs to get down to the hex plugs. Once I had the intake sprocket off, I was 99% sure I had found the leak, but it was only the four exhaust cam bolts, four little bolts, a stud and the upper belt idler to get the metal timing cover off and get to the hex plugs, so I kept going. It'll give me a chance to clean all the mess up, anyway.

I'll make a big order of parts from Courtesy Monday. I am also going to put brakes on the front end, as it has started shaking pretty bad and the wheels are up in the air, anyway. Figure end of the week for parts, so it'll be a week or so before I get it back together. Will report back again on whether that fixes the leak.

[DeeZX]

I found the oil leak a while ago. It was the VTC cam gears that were leaking. the reason why it was so mysterious was the oil would be sprayed every where while the VTC Cam gear rotated. I got them Tig welded as a temporary fix to stop the leak but eventually replace the cam gears with BDE VTC cam gears. I used the welded gears for about a year without any issues. I posted about it on a different forum I think, or maybe it was this same forum, different post with pictures of the welded cam gears. if I can find it I'll link it.

Edit: It was this forum. Here is the link: leaking-vtc-cam-gear-sprockets-repaired ... l#p5736155

[MikeCTTZ]

DeeZX, thanks for replying! I actually saw your TIGed gears and was wondering how that worked out. I have a TIG welder (and know how to use it), so I considered zipping these up, but wanted to know if it worked for you. Seems it might be a solution. Gotta wonder why Nissan didn't weld or furnace braze these pulleys/gears to being with. My only concern about welding them up is getting ALL the oil out of the seam so it doesn't pinhole.

I don't know yet if my gear is leaking or if it is just the seal. I'm going to round up some plumbing bits tomorrow and make up a pressure tester to see if the gear is leaking around the rim of the insert. I know what I am going to end up doing, though... BDE gears. I don't want to screw with this ever again.

[MikeCTTZ]

Hmm, a little digging has me even more inclined to get the BDEs, rather than TIGing up my old ones. There's a rubber O ring in there behind the hub. Unless you can take the pulley apart to get that O ring out, the rubber is going to contaminate the weld and make it nearly impossible to get a real good seal. I could give it a try, and it sounds like it worked for the OP, but having to go BACK into the front end of the engine again is just not worth the risk. I just want to drive the damned car for a while, instead of working on it.

[MikeCTTZ]

Hey all, I am not going to be one of those that asks for help and never responds with the results... I got my parts in, 120K kit and BDE pulleys, but they shorted me one of the bypass hoses on the timing kit. Grrrr. Last weekend I swapped the cam seals, the crank timing gear and the idler studs, but can't go any further until that one little hose gets here. Probably be middle or end of this week before it arrives.

BTW, any of you planning on doing this 120K yourself... Beware and prepare for the worst. I had a HELL of a time getting the crank pulley off. It had corrosion under it and was stuck solid... so solid I had to heat it with an oxy/acetylene torch and pry/tap on it to get it to move. I wasn't too worried about the heat, as the mass of the crank soaked it up very quickly after the torch was removed. It never even got hot enough to damage the seal (which I was replacing, anyway). I got it about halfway off and then had to chain drill a string of closely spaced 3/16" holes between the teeth that hit the keyway. Put a chisel in the last hole and gave a light whack with a hammer. Gear split instantly and came off with my fingers. Cleaned the corrosion off and the new gear slides on and off with your fingers. (Keep in mind, this car was "meticulously maintained" by a VERY reputable shop in town that works on exotics and high end cars.)

The new gear is going to get a pair of small holes drilled and tapped in the face before it goes back together so it can be removed with a puller, if this happens again. I would have drilled and tapped the old gear, but there was not enough room to get a drill in there between the A/C condenser and the nose of the crank, and I didn't have a 90 degree drill.

Also, the idler studs are locktited in. You can forget backing them out with two nuts jammed together. There's almost no way to get them out without heat. Just laying on them is going to risk wringing them off in the block. I put the torch right at the base of the stud and heated it red hot, then let it cool until the color went out and managed to back both out with a pair of big vise grips around the unthreaded shank.

Scary having to break out the torch on my Z, but sometimes heat is the right tool for the job.

[nissanfreak12]

Try soaking it with WD-40, this usually breaks down loctite. Also look for a stud remover, that is how I got mine out. Generally they are cheap, but don't get the cheapest one possible, you will hate life at the moment if you do.

[MikeCTTZ]

I even tried Kroil and it didn't have any effect on the locktite. I deal with a lot of locktite, as I work as a machinist for a company that repairs/makes hydraulic cylinders. WD may work on some grades of locktite, but none I have seen. Having WD on there might prevent galling when it does break loose, but locktite is practically inert to anything except heat once it has hardened. It's not much different from super glue.

I wish I had a nice collet type stud remover/installer. Had one at another job several years ago. Also had the simple three finger Van Norman style which worked well, but was a little rougher on the stud. And yes, a cheap one can make your life suck real quickly, as can wringing one off. I even have left hand drills for broken bolts, but you can forget that on a locktited stud. It'll drill a hole, but the remains are not going to back out, even with an EZ out. Have to drill it as far as possible and then (if you are well centered) pick out and end and peel the thread out like a wire. If you aren't well centered, it's not going to be fun and you'll probably end up helicoiling it.

[t.mcginley.jr]

BTW, any of you planning on doing this 120K yourself... Beware and prepare for the worst. I had a HELL of a time getting the crank pulley off. It had corrosion under it and was stuck solid... so solid I had to heat it with an oxy/acetylene torch and pry/tap on it to get it to move. I wasn't too worried about the heat, as the mass of the crank soaked it up very quickly after the torch was removed. It never even got hot enough to damage the seal (which I was replacing, anyway). I got it about halfway off and then had to chain drill a string of closely spaced 3/16" holes between the teeth that hit the keyway. Put a chisel in the last hole and gave a light whack with a hammer. Gear split instantly and came off with my fingers. Cleaned the corrosion off and the new gear slides on and off with your fingers. (Keep in mind, this car was "meticulously maintained" by a VERY reputable shop in town that works on exotics and high end cars.)

Are you talking about the actual crank pulley, or the smaller crank sprocket?

As for the idler studs I actually did remove mine with 2 nuts jammed together, but only after doing several heating cycles with a torch and WD-40. I've had to use a torch + WD-40 on a number of things like this, not a big deal as long as there's no rubber or plastic around.

[MikeCTTZ]

duh, yes.. crank timing belt pulley/sprocket. I made a puller for the front pulley when I did this the first time. It was not an issue at all.

[MikeCTTZ]

Car is 99.999 of the way back together. Would have driven it tonight, but when I picked up antifreeze this morning, I screwed up and got a jug of that @#%^ing orange 50/50 mix long life Chevrolet crap. I only got a splash in the radiator before noting the color, but I am just going to buy about 5 gallon jugs of distilled water and flush everything out clean to start over.

As usual, I cranked it soon as I got the belt in place to make sure the timing was right (made that mistake first time I did this, 12yrs ago and had to take it apart... crank sprocket was one tooth off). Got it right first time this go around. New oil cooler lines, a new PS return line down beside the AC compressor, full 120K kit and an oil change. Going to do brakes in a week or so.

One reason it took so long to get this back together was thanks to Courtesy Nissan parts department. After getting my BDE timing gears and starting on the car, I discovered they had shorted me one of the bypass hoses. That was Thanksgiving weekend, so the part didn't even ship until late that next Monday. Got the parts Wed, thanks to priority shipping, so I started putting everything back together last night. Got a fair amount done and intended to finish today. Last thing to do before putting on the timing belt was to install the springs and caps on the VVT gears. WTF? Courtesy only sent me ONE new spring. I fired off a nasty email and decided to just re-use one of the springs (true to their name, they were very courteous in telling me they were sorry). I checked the uncompressed height and it was identical to the new one. Use a little set of scales and measured pressure at a given height and they also matched. Screw it, the car is together.

I'll know if my oil leak is fixed soon as I drive it and park it back in the garage. Will report back mid week.

Next question... anybody ever had the rack out of one? My steering shaft seal is leaking like a sieve. We are talking 1" puddle in a half hour leaking (real bad). If I can get the rack out, I am going to just rebuild it. Kit is $50 and I work at a hydraulic shop. Seems pretty obvious. My primary question is, can you get the damned rack out of the car without pulling the engine? If you can't the get the rack out with the engine in it, I'll figure a way to get that seal out as it sits, but I'd rather fresh up the whole works.

[MikeCTTZ]

Just got back from the first test drive. Looks like I have fixed nothing. Still drooling oil from the same exact location. I'm probably going to sell this car. It's not fun anymore.

[MikeCTTZ]

Just got back from the first test drive. Looks like I have fixed nothing. Still drooling oil from the same exact location. I'm probably going to sell this car. It's not fun anymore.

[MikeCTTZ]

Update, my despair may have been a bit premature. After finding what seemed to be the same leaks, I decided to hell with it, I'm going to drive it. Pulled it in the shop earlier this evening and it looks like I did indeed fix the leak on the front passenger side with the new BDE pulleys! Also not a drop from the rack! I can only guess the pools of oil I was seeing was trapped oil draining out for a few days after the leaks were stopped. I am in a much better frame of mind now, but the work is not quite yet over....

Bad news is that it looks like either the last shop damaged the rear main when they put in a clutch/rebuilt the turbos, or the screwed up PCV blew it out because the rear main is obviously pouring. Big puddle at the intersection of the bell housing and pan. Just have to see how much of a PITA it is to get the transmission ouf of this one.

On a separate note, my car had always had the typical low oil pressure issues. I am thrilled to report that I am now running DOUBLE the oil pressure at idle and 2000rpm it had before this work session. Only things I changed were those pulleys and going to a different oil filter (Purolator Gold). I really think those pulleys were bypassing oil pressure internally, but we'll see.