Burning oil, where from?
 

Hey guys, here's the deal. After a long downhill, or any kind of good engine braking (leaving it in gear after a hard pull, engine braking down hills, etc) the car burns oil. For instance when I engine brake down a long hill, once i get on the gas at the bottom of the hill it gives me a good poof of smoke and I get to smell it.

Here's what I know. I know my compression results came back 150-155 across all 4 on an HF gauge, and deviated less than 5 psi between wet and dry tests. I know my catch can does not accumulate much oil at all, in fact after 700 miles there's barely a tablespoon or two of oil in the bottom. I know that pulling off the oil fill cap and revving the engine does not give me any smoke or pressure through the fill cap. I know that the car does not smoke noticeably under power.

The oil consumption is somewhere between .5qt to 1qt every 1,000 miles, depending on how much engine braking i'm doing.

Now knowing all this I believe my oil consumption is either due to valves or turbo seals. I had the stock greddy oil return line on this turbo for the longest time, and I know for a fact it wasn't draining correctly at least part of that time. I've actually popped the hood to see oil smoke coming from the CHRA of the turbo.

I also know the car does not smoke on startup after sitting (which as I've read is typically what dying valves do).

This leaves me to start to think it may be the turbo. Now my main question here is, HOW can I go about testing this? I don't want to order a rebuild kit for my turbo if it's just valves, and I don't want to pull the motor if it's just the turbo. I need a good method to determine where my issue is.

Will a leakdown test tell me? My only other though was to source a header and go turboless to see if it still smokes. I'm hoping there's an easier solution. What do you guys think?

Thanks,

TL;DR: How can I diagnose whether it's my valve seals or my turbo causing burnt oil on deceleration?

Sounds like intake valve seals to me. Matches your symptoms.

I'm trying to think of how a CHRA leak would produce those symptoms and am coming up blank. I think a CHRA leak would produce oil smoke during the closed throttle operation (not the puff when you open the throttle) because the turbine is still plenty hot enough to flash the oil.

Thanks for the reply. I definitely smell the oil on deceleration, so its burning before I open the throttle. But when I open the throttle again is when i get a noticeable poof from the exhaust. It may burn a slight amount during normal driving, but nothing I can notice from the cabin.

I'm on the hunt for a motor now, hopefully the turbo is still good so I can sell the kit. I really need to verify this before I pull the car apart anyways so I know what's good and what's bad. Leakdown test should detect valve seat issues, correct?

Yes. You'll hear it in the intake or the exhaust, and that will tell you which side. Chances are, it's both. Since teardown is a pain in the ass anyway, might as well do them all at once.


Edit: it's the stem seals, not the seats.

Hey guys, buying a leakdown tester. I really would rather spend as little as possible on it, but I know how crappy harbor freight/ebay can be. Can i get away with an cheapo leakdown tester? I found one here, what do you guys think.


Engine Cylinder Leakdown Tester Dual Gauge Diagnostic Kit for Imports Domestic | eBay

I have a thread I made...(give me a minute, I'll find it) where I built one after watching a "how to make your own leak down tester" on YouTube. It worked great for me...

here:
https://www.miataturbo.net/engine-pe...hat-now-64069/

Wow, thanks Thirdgen. That's a cool thread. I dont have a welder atm, so i'm looking to purchase a pre-built unit - but i do like that idea for the diy cheapness of it.

Anyone else have any recommendations on a budget leakdown tester, or any experience with ebay/hf units?

Edit: Actually found a few different units I'm considering over the ebay one. They actually are brand names.

Proform leakdown tester:

http://www.ebay.com/itm/Proform-6683...#ht_1342wt_934

Summit racing leakdown tester:

http://www.ebay.com/itm/Leakdown-Tes...ht_1666wt_1166

Edit 2: I think I trust the summit racing one more. This is a tool I want to add to my collection, not just use once so no ebay/hf this time.. I like to think I've learned my lesson after buying cheap tools before. Anyways i like the fact that it has two 100psi gauges and that you calculate the leakdown percentage yourself.

https://www.miataturbo.net/attachmen...ine=1345153968

Fire, valve guide seals (or valve stem seals) have nothing to do with valve sealing. They just prevent oil from running into your intake past the valve stems when you've got vacuum. A leakdown test won't detect this as it has nothing to do with compression.

??

Are bad valve seals something that gets worse with boost, or is it pretty much a steady demise? I have a similar issue to fireindc but only if I stay at high-vac after a WOT pull (like if I pass somebody then stay in third to engine-brake back to a reasonable speed). No smoke, I just smell it a little with the top down. My other thought was a bad PCV valve, since I don't run a catch can or anything.

Damn, thanks for the info. So how in gods name can I diagnose bad valve guide seals?

Skidude, sounds like my car. I can smell oil after a hard pull if i keep it in gear, if i throw it in neutral after a pull i don't get the smell.

When mine began to fail in the Talon I'd see a puff of smoke on startup after having parked it for a while. Even after idling for 15-20 minutes I'd see a little when I drove off but nothing like after it sat. I also had smoke on decel after WOT, which I thought was bad turbo seals. But that exact same turbo is on my Miata and not smoking so that must have been the seals too.

Is it a Miata? Does it have close to 100k or more on it? You have bad valve seals. Simple as that. It's a known maintenance item.

I never get smoke on startup no matter how long she sits, and it seems that for most people that's the indicator. However I have 170k on the stock head so that is probably the problem. The bottom end had rings/bearings put in at about 100k miles due to snc failure, but the head was left untouched.

I'm going to leakdown test the motor then determine what I'm doing from there. If it has good leakdown results, I'll pull the head, drop in some new valve guide seals, and have the head decked to raise compression. I'm hoping bumping compression will give me some spool gains.

If the motor doesn't leakdown good, I'm going to find a 1.8. Thanks for the help bros.

Why not pick up a set of valve guide seals from Rockauto or someplace for like $20 and change them out on the car? AFAIK all you have to do is remove the cams & keep the valves from dropping while the keeper is removed. Shouldn't take more than a couple hours and maybe $40-50 after you buy the tool to remove the keepers/springs.

Looking into the details of doing this, thanks SJP. Still thinking I'm going to leakdown this thing before I put any more effort into it. However, compression was even with little drop between cylinders and very little change between wet/dry. So maybe I'm overthinking this.

I think I'm still looking for an excuse for a 1.8 swap. At the same time I really don't need it. Thanks for the tips.

Resurrecting...
I was just reading your thread on seeing a puff of smoke when hitting the gas after a long period of engine braking. Was wondering if you ever found the problem? I'm seeing the same and have replaced the valve stem seals and no help.