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225 Advice - blue smoke
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Author:  KEC [ Wed Jul 29, 2026 7:02 pm ]
Post subject:  225 Advice - blue smoke
Hi
I've got a 1986 225 slant 6 with 79k on it that was blowing blue smoke after a day around town both at idle and under load. Oil pressure was dropping to 40psi at idle and up to 60psi while under load. Plugs looked okay, not wet but some carbon fouling. Took it into a shop to get the cylinders compression test done, dry test came back 105 on all 6 and they are doing a wet test in the morning.

I've been using her as my daily for the last few weeks with the odd problem here and there. First thing I did was replace the PCV valve which didn't change much which leads me to think its going to be the piston rings or the valve stem seal (both of which I might as well change in one go).

My biggest problem is I'm 22 with not alot of savings behind my self having just relocated from overseas, I've got plenty of mechanical experience, but still always trying to learn (I've rebuilt my old 62 MG B and a Jag mk II back home with no problems). Im working 4 on 3 off, 12 hour shifts which really restricts my down time.

I've bought most of the tools to get it done, i just dont have the space to pull the motor, or the justification to buy a engine crane and stand for a (hopefully) one time job (I understand its ideal it get the head machined, but as compromise I've got a pane of glass). So my question is, Is it possible to do the rings and seals without pulling the engine ( hoping the cylinders only need a honeing and not a boreing/resleve) or do I send it to a shop and hope they don't burn a huge hole in my wallet. Or another option is do I move her on to someone who has the time and money to do it (not my proudest choice). I would really prefer to do it my self but at the end of the day I can only do what I can ( mainly financially, Ive got a bicycle for the down time problem, just inconvenient)

Normally I'd ask the old man for advice as he taught me everything I know but hes not around no more so hoping one of you are willing to help a young fulla with some advice to keep this old classic running well. It would mean alot to me. Thanks all.

Attachments:
File comment: The MG B back home
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File comment: The old girl
The pride and joy.jpg
The pride and joy.jpg [ 112.57 KiB | Viewed 692 times ]
File comment: Plugs
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Author:  SlantSixDan [ Wed Jul 29, 2026 7:34 pm ]
Post subject:  Re: 225 Advice - blue smoke
Welcome here.

There is no reason to think you might need to plane the head, so don't fret about that. Fairly good odds you won't need to take the engine apart.

40 to 60 pounds is much more than plenty of oil pressure. It's actually kind of suspiciously high; what grade of oil are you running? It will be a good idea to service the oil pressure relief valve to make sure it's doing its job, as described in these two threads: thread 1, thread 2.

Those spark plugs don't look bad at all, actually. I'd expect them to be much muddier if you're burning significant oil.

So the first thing to confirm is that the blue smoke is coming out the tailpipe, and that it's not oil from the engine or transmission leaking onto a hot exhaust component and burning that way. One question: does this truck still have its catalytic converter(s)?

Assuming the smoke is coming out the tailpipe:

• your valve stem seals are four decades old, so pretty good odds they're not at their best, but if they were bad enough to cause (all of) your oilsmoke, you'd get a cloud of blue on first startup after an overnight or several-hour shutdown as the primary symptom; bad valve stem seals don't cause oilsmoke under load.. So yeah, by all means, go ahead and replace the valve stem seals. This is an easy operation with the engine in the truck, and you don't need an air compressor. See here (disregarding the verbiage about adjuster screws; hydraulic-lifter engines like your '86 don't have them).

• Your compression readings aren't alarming, and they're consistent, which is important. Let's see what the wet test shows, but if I'm seeing 105 on all cylinders, I'm not thinking a ring job is at hand. If you've got ring issues, this points more at the bottom (oil control) rings and less at the top and middle (compression) rings. This would stand to reason; an '86 with only 79k miles on it has sat unused for long periods of time, and/or had a lot of short trips, both of which will tend to sludge up the oil rings and stop them doing their job.

I think in your shoes I might be tempted to try a careful and thoughtful engine cleanout. Buy several filters ahead of time, and get the big-big ones for this purpose (Wix 51773).

You mention the PCV valve. That's a good item to have replaced, but make sure you got the correct one in good quality, because many of them look and fit alike, but the wrong one makes problems. Also make sure the crankcase breather (at the top-rear of the valve cover, with hose to air cleaner housing) isn't clogged up.

(Nice truck! Reminds me of my '89. Can't quite see from here, but I have suspicions about the headlamps on yours ;-) )
Author:  Rick Covalt [ Thu Jul 30, 2026 8:13 am ]
Post subject:  Re: 225 Advice - blue smoke
How much oil is it burning/using? I guess not much with the way the plugs look. Any chance it has old gas in it? oil pressure at idle could be 20# and not be a real concern.
Author:  mcnoople [ Thu Jul 30, 2026 8:41 am ]
Post subject:  Re: 225 Advice - blue smoke
There is a lot of good reviews of an oil product called valvoline restore and protect for stopping oil burning. It is a motor oil not an oil additive so you would use it during a normal oil change service. You would want to change the oil filter repeatedly to prevent clogging.

I am currently using it on my spouses acura mdx with the 3.7 liter engine. This engine was known to have big issues with oil consumption. I am about 2000 miles since adding oil and still mostly full. So my personal experience with it so far has been good, it used to be a 1qt per 1k mile oil burner.

And the best part is that this is the first oil change I have used this oil, valvoline claims it takes 4 oil changes to work its full magic. I am sure that this oil in the proper viscosity oil would be vastly superior to what was available when the slant was designed. Just make sure to change filters before they clog.

If you find lots of sludge up top when you pull the valve cover to replace the previously suggested valve seals then I would likely also pull the oil pan and clean it out by hand. This will keep crud from circulating if it starts to dissolve from any solvents/cleaners.
Author:  SlantSixDan [ Thu Jul 30, 2026 10:49 am ]
Post subject:  Re: 225 Advice - blue smoke
Careful with "restore" types of products – mostly they work by softening and swelling rubber seals, the idea being that oil leaks through worn, hardened/shrunken seals. But by softening and swelling them, you make them much more prone to wear; it's not 'magic', it's a temporary get-by. There is nothing such as engine restoration in a bottle or can. You do or don't have to refurbish or replace parts; if you can't get the existing parts to clean up and work right, then you'll have to go into the engine. A "restore" type of product can buy you some time if you have a vehicle with two wheels in the junkyard and you need to squeeze the last bit of life out of it, or if you need time to get things organized and arranged for engine work and in the meantime it's losing too much oil to be practical, but none of that sounds like your case.
Author:  mcnoople [ Fri Jul 31, 2026 7:35 am ]
Post subject:  Re: 225 Advice - blue smoke
Quote:
Careful with "restore" types of products – mostly they work by softening and swelling rubber seals, the idea being that oil leaks through worn, hardened/shrunken seals. But by softening and swelling them, you make them much more prone to wear; it's not 'magic', it's a temporary get-by. There is nothing such as engine restoration in a bottle or can. You do or don't have to refurbish or replace parts; if you can't get the existing parts to clean up and work right, then you'll have to go into the engine. A "restore" type of product can buy you some time if you have a vehicle with two wheels in the junkyard and you need to squeeze the last bit of life out of it, or if you need time to get things organized and arranged for engine work and in the meantime it's losing too much oil to be practical, but none of that sounds like your case.
I totally agree with this, but would like to point out that it is already suggested to replace the valve seals in this thread. The only other rubber seals in a slant are front and rear mains. The front seal isn't too big of a deal with timing chain replacements being common.

Rear seals are more of an issue, but do the seal swelling products have any effect on original style rope seals?

As far as the valvoline restore and product is concerned. I am trying it because my mdx (known for stuck oil rings) would burn around 4-5 qts of oil during a 6k oil change interval. I changed to V R&P with the last oil change a few months back. I did not change the filter at that time. I changed the filter after 400 miles and again 400 miles later. I topped it off at each filter change. I checked the oil this morning while pumping gas. It was 1/4-1/2 qt low. It has been a little over 2k miles since the last time I added oil and around 2800 since switching to V R&P. I am not much concerned with "other" problems on the engine I have already changed out all of its common to fail rubber seals.

There are many videos of people with similar results including before and after shots of valve train cleanliness. The convenience factor of just using an oil to clean internal components is worth considering. But it is not a magic bullet and needs to be done properly.
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