Using STP or motor oil thickeners, on old engines

on my '91 mazda B2200, w/ carburetor intake, 179K miles, running great, 20 mpg in town . . .

when i start up (specially if i’ve parked vehicle with engine on downhill side of > 10 degree incline) lots of blue smoke from exhause pipe . . . for a few minutes. then it clears.

i think it’s oil getting past the valve guides, due to the way cold oil circulates at startup.

Question: is there some big caveat or warning about using a can of STP in the oil. i’m thinking STP would minimize that ‘loose tolerance’ problem, enough to be worth trying.

or, is there something better than STP.

or is this a bad idea?

thanks for any insight or personal experience accounts.

michael w.

I wouldn’t use STP, I’d try one of those oils for older engines, like Valvoline MaxLife. It sounds like valve seals, and that kind of oil might swell them slightly, reducing oil leakage. Or you could see what it costs to get the seals replaced, the head can stay on the engine.

Many of us have had old “tired” engines that we didn’t want to invest any money into. I used STP in many cars when it first came out in the late 60s. It’s one way to thicken the oil in your crankcase. Another way is to just buy thicker oil.

Thick oil often does diminish the blue smoke symptoms you describe. However it also starves your engine bearings for oil during startup when the engine is cold. If the engine is “tired” anyway, I wouldn’t worry too much about that.

However, STP will make it more difficult for the starter to crank the engine in cold weather. You might want to first try something like a 20-w-50 oil, which will give you the thickness you desire when hot without having cold 50w oil when starting a cold engine. If that fails and you’re still determined to get rid of the smoke, then dump the STP in.

[In high school, I had a Corvair that smoked and burned oil like crazy. After adding 3 cans of STP, the smoking stopped completely and the oil consumption minimized greatly. It was a bandaid but it kept an old junker going.]

Update: I read Texases reply about trying an oil designed for older engines (they’re good at swelling worn seals). I agree with Texases that it’s an option worth trying, especially since you don’t know the exact cause of your burning.

My vote is for trying one of those high-mileage oils (in the proper weight) before trying anything else.

high mileage oils?? what are those?
thanks for a ‘definition’ of 'em.
as i stated, i think the mazda engine problem is worn valve stem guides–naturally the general engine wear would be commensurate with other worn parts. however, it’s not so bad (e.g. rings) that smoke continues after a minute or so.
i don’t know the wisdom, engineering-wise, of going to a heavier motor oil. that suggestion is a version of the STP solution i’m trying to learn about!

i hoped to hear from someone who actually had the symptoms i described, who did use STP or another ‘thickener’ and could report some results, empirically!
thanks tho. m.

I think you are correct in assuming oil getting past the valve guide seals, and the valve guides.

Since you said that it mostly happens when you have the front of your truck parked on a downhill slope, that means that there is oil gathering in the very front of the valve area.

It might also be that your engine either doesn’t have a drain hole in the front, or if it does have a drain hole in the front, that it is clogged up.

I think it would be worthwhile to pop off the valve cover when the engine is parked on that hill for a couple hours, to see what things look like under there.

Who knows, you might just need to either unclog a drain hole, or just replace the valve guide seal on the front cylinder if only the two valves for that one cylinder is covered in oil.


The incline making it worse makes me suspect sludge.
Remove the valve cover and make sure the passages to drain the oil down from the head are clear.

For Pennzoil, it’s High Mileage Vehicle. For Valvoline, it’s MaxLife. For Quaker State, it’s Higher Mileage Engine. If that doesn’t cover your favorite brand, check their web site.

didn[t mean to say ‘inappropriate comment’ here.
i always pour the oil in from above the galleys in the head, after all, when i change the oil. therefore, since within minutes it is measureable on the dipstick as the prescribed 4.3 qts, i assume there is no blockage from top of head to bottom of pan, or to where dipstick measures!

on sludge–absolutely not, no way, niente, nada, zippo;
absolutely clean pan, always used the spec’d castrol 10W30, virgin clean like honey.
hmmm, on valve stem seals, tho.
. . . supposing the 91 mazda b2200 does indeed have them as part of that valve train engineering system.

An old acquaintance of mine had an even older Chevy C-20 van (350) that he religiously added a can of STP with every old change from when it was NEW…The old Chevy went 350,000 miles without ever taking the heads or pan off. No cam or lifters either…And it was still going strong when he moved away…I don’t know if the STP had anything to do with it, but it SURE didn’t hurt anything…

Another little factoid… When resizing rifle cartridges in a swedging die, a special lubricant must be used or the casings will jam in the die. Normal oil, even heavy gear oil will not work in this application. But STP worked just fine in place of the “special” die lubricant…So I suspect STP has lubrication properties in addition to being a VII…

i know nothing about resizing cartridges, or properties of lubes needed. what is a VII . . . ? is that an automotive spec? i used STP in a 63 VW 1800cc engine regularly, and in other old engines, such as flathead dodge 6.
but those, and the older C-20 etc are of a vintage of engineering before the computers took over and absolutely maxed out the tolerances in friction surfaces (and everything else, viz, the unibody).
that’s actually why i ask about the STP in the 91 mazda–it’s new enough to be engineered to very close tolerances (hence my good performance at 179K miles, and i only change oil about every 5K miles; absolutely nothing else on the motor, not tune up nothin’; oh, i did replace the timing belt when i got the thing used at 77K.
anyway i’d have no qualms at all about dumping a can of STP into the mix, except for my superstition that it could be a problem for such friction wear points as main or con rod bearings–maybe i shdn’t worry. how much damage can one STP pint do?
well . . . hmmmm. i don’t know. no doubt it couldn’t hurt the problem i suppose i have, the worn valve stem guides.
oh, one other datum, if i let the oil get low i can hear the ‘tappets’ for a few seconds. in fact i must say, as i get attentive here, it uses some oil–maybe a quart in 500 miles. but my informants in the rear all tell me they see no tell-tale blue wisps as i go down the road.
thanks for your note.

VII…Viscosity Index Improver. That’s what turns #5 oil into 10/30 or 10/40. But the OIL is still 5 weight…

yikes, what am i thinking, or saying? i meant dodge slant-six, not flathead! good thing i don’t mess with cartridges, i’d hurt myself.

My fascination with firearms was a passing thing…My next obsession was radio controlled model airplanes, but that passed too…It’s interesting that Rossi makes a fine shotgun and an equally capable model airplane engine…

one of my first fascinations, from preelementary school days, living on a farm, looking up into the west texas skies, was . . .
specifically those yellow piper cubs a couple of the ranchers had.
remote controlled models comes damn close.

Are you afraid of the stem seals? You could replace them. They are certainly dead by now. At some point the engine has had enough despite the treatment stuff is out of spec and it can be patched, shot dead, or rebuilt. You can do stem seals not too much work. Rebuilt heads, Can be done easy. STP not likely to fix the problem for more than 5k miles at this point. Still you need a new ride if $5 is your limit to fix this one.

Read the sticker on the hood. Some of the old Mazdas required 30 WT oil with 40 WT as an option. You would never need STP if your engine says to use 30 or 40 weight oil when temperatures don’t go below 30 degrees F. You can’t pour 5W30 into everything.

If temps where you live get below freezing then I would NOT suggest using STP. It’s WAY TO THICK when temps drop below freezing. STP would be almost like tar at that temp.

Won’t STP mix with the oil in the engine therefore it would not be like tar?

that’s what i thought!! it would MIX with the oil. sure! sez i.

but, it would still be like tar, in a way, cause tar will mix with oil, it the temperatures are high enough.

anyway, the question isn’t about tar or reading oil specs on hoods.
it’s about using a can of STP in a '91 2200 cc engine of the conditions i described.