STP Oil Additive good or bad?


#1

Just out of curiosity, what do you guys think about those Oil additives that STP and others make ? I was wondering if it would benefit my Elderly Honda engine or if it would do more harm than good. Thoughts and ideas? How about the “complete” fuel system cleaner ?


Steel building for an car garage!
#2

STP is a “Viscosity Index Improver”. Translation: It will make your oil thicker.

How thick? Nobody can predict this, as we don’t know the current viscosity of your oil. All I can say is that I would personally avoid this stuff, as you could wind up with oil that is too thick to flow properly, particularly if temperatures drop. And, if oil doesn’t flow properly, you could wind up with lubrication problems, and that could spell an early demise for your engine.

As to a fuel system cleaner, if your engine is in need of this, the only two brands that I would recommend are Seafoam and Techron (by Chevron). The other fuel system cleaners don’t do much of anything except lighten your wallet, IMHO.


#3

I always recommend against STP, unless you have a wornout engine and you want to get one more summer out of it. I’ve never used STP since my student days car (57 Plymouth, well worn) and have not overhauled an engine since the summer of 1964. Modern oils have all the aditives you need. Fuel system cleaners (the ones that work)are a good idea every 30-40,000 miles or so.


#4

I have a slightly different take on STP. Many ago I was responsible for all operational decisions and work in a very large high speed production plant. I had my guys just finish a major “to the floor” overhaul of a production line. We had just started it up and were running it without making product and at low speed to work in all the hand-scraped main bearings etc., etc. When I told them to speed it up to full speed I had them run it for and hour or so and on one of the machines in the line driven by a 50 HP motor with a forced oil lubrication system I had our electrician check the current draw on the main drive motor. I then had STP put into the crankcase according to the mixing instructions and after it was thoroughly mixed into the motor oil I had the electrician check the amperage the motor was drawing. I do not remember the exact figures but the current draw was about 20% less. Since only about 10 minutes had elapsed between the two and since the speed was not changed I concluded that the significant reduction in amperage was the result of reduced friction. This machine had three large crankshafts that operated the mutitude of mechanisims on the machine. To me reduced friction was good - very good!
So based on this I believe that dismissing STP as worthless is open to discussion.


#5

A production floor INSIDE is far from real world experience. Tell me how well STP works when you try to start you car at 5am after it’s been sitting all night at -15. IF it even turns over there’s a very good chance it’ll be toast long before the engine reaches operating temps.


#6

You don’t need this additive unless you have a near worn out engine.
Mike is exactly right about STP and cold winter days. It’s going to work the battery and the starter motor much harder; if it starts at all.
Many years ago I worked for a small town Subaru dealer. Subaru at one time required, and paid for, an manual transmission oil change at the 1000 miles mark along with several other little chores.
Our sorely lacking service manager INSISTED that every trans oil change (they used 80/90W hypoid oil) also get a can of STP oil treatment with it.

You can just imagine what shifting a transmission was like on a zero degree day, much less a 15 below one, with STP diluted 90 Weight gear oil.
The best analogy would be rowing a boat through a tar pit.
One could even notice it when the car was decelerating since it gave the feeling that the brakes were half-applied.


#7

For the oil thickening, you don’t have to mix anything, pour anything into a running engine or jump through any hoops. A can of straight 30W motor oil is the same price as any other quart of oil. Two quarts will thicken the mix even more. Don’t work harder or expensiver; work smarter. If you have the CVCC engine; mine did well on five quarts of 30W and got 36 MPG highway. 1.8 engine in an 82 Accordion.


#8

Two facts. A friend of mine had a '78 Chevy van with a 350. He changed the oil twice a year and always used STP. last time I saw that van it had 380,000 miles and was still going. It was on it’s third transmission… The heads and oil pan have NOT been off this engine.

When resizing cartridge cases in a die made for that purpose, Only two lubricants will work to keep the brass cases from sticking/jamming in the die. A special and expensive die lubricant or straight STP. Other oils, even 90 weight gear oil, will not prevent sticking like STP does…

STP. Scientifically Treated Petroleum… So what is the downside? When it burns in a worn engine, it leaves a LOT of deposits on the spark plugs and exhaust valve stems…


#9

What about your elderly Honda engine do you believe needs help?

If it is not broke, don’t fix it.


#10

What year honda? What size? How many miles?


#11

STPs label once read THE RACER’S EDGE. Well, racing engines are LOOSE engines. The clearences for pistons and bearings are very loose and require a great volume of oil and a thicker oil. Late model engines are built to very close tolerance with very tight clearences which call for thinner oils. I have seen Japanese engines fail to run when temperatures dropped below 10*F due to thick oil pumping up the lifters, preventing the valves from fully closing. Also,when tearing down a seized 4 cylinder Ranger engine one cold January I found the oil pump drive shaft twisted into a cork screw and lying in the pan. The driver used 20-50 oil and one of the molasses additives.


#12

STP is an interesting product, and few people understand it, so let’s get rid of some of the nonsense. First one person said to thicken oil simply use 2 cans of 30 weight oil, this isn’t a good thing to do for modern cars where the owner’s manual recommends 0-20 or 5-30, straight 30 could cause some fatal damage to engine. Now try this, take a can of 30 weight oil, or even your favorite oil regardless of weight and get some on your naked, yes that’s right I said naked, index finger and thumb and rub them together, feel how slippery it is, then wipe the oil off with a rag and try doing the same thing with STP, you will discover something interesting…it’s slippery then your engine oil even though it feels a bit thicker. I would not use any oil additive in a modern car due to the tight tolerances in engines today, but if you have an older style engine from the 1980’s and older and you have issues with it burning oil than STP might help to reduce the oil burning.

I think too that with modern engines that use 5-20 or 5-30 engine oil as the miles tick up eventually you will want to shift to a high mileage oil at probably around 100,000 miles; and shift to the next higher weight oil, so from 5-20 to 5-30 for example, when it starts using more oil than normal. 5-30 is still thin enough to be plenty safe for winter use. Typically you should never use any oil thinner or thicker than the car manufacture states to use, but when the car starts to use more oil between oil changes that is due to more space, or slop from wear going on inside the engine, at that point it has enough wear that the tolerances aren’t as critical as they once were and the next step up in weight won’t hurt the engine and will protect it longer. Once you go to the next thicker oil you’ll need to watch the oil usage closely to get a baseline, once you have that and later, say 100,000 miles later and it’s using more oil than what that baseline gave you then you can go to the next weight up like 10-30, by the time you get to that 10-30 weight oil you should be pushing around 300,000 miles depending on how the engine is using oil of course. Most new cars today do use oil naturally as brand new engines so you have to know you vehicles oil usage really well because you don’t want to jump up to the next weight shortly after you get the new car, that thicker oil could ruin your engine and void your warranty on top of it!

I had a vehicle once that never used any oil between changes for 240,000 miles! So all I did was switch to a high mileage oil at the 100,000 mark. I sold the vehicle so I don’t know how long the engine either lasted or if it started to burn oil at some point.


#13

Nonsense. My 05 4runner and wife’s 07 Lexus both called for 5w-30. Sold 4runner a few years ago with over 300k miles. Always used 5-30. Wife’s lexus has over 200k miles and still using 5w-30 and oil is right near the top line when I do an oil change every 5k miles.

I wouldn’t follow that advice. First off if the engine was properly maintained there shouldn’t be any slop as you say. Second - a thicker oil may be too big to get oil flowing correctly through the engine oil journals.

Gee - only 240k miles?


#14

I gotta agree with @MikeInNH I only used the stuff once about 1968 in my 59 Pontiac. I’m not sure why but I poured it in in the winter and luckily the engine was running. Otherwise it would have just been a heavy glob somewhere in the engine. Took about 5 minutes for it to pour out.

It was usual for me to get 2, 3, 500,000 miles on my car and I never switched to heavier oil than was specified and I never had excessive oil use or hardly any oil use. Well except for my diesel that is, but that was a different issue. So just use the spec oil and change regularly and forget all the additives.


#15

I bought a small bottle of STP engine additive and kept it in the trunk of my car over the wiinter. Today I decided it was time to use it. To my surprise the additive was frozen solid. Not sure whether or not to use it when it thaws.


#16

If you have doubts then don’t use it . It is that simple.


#17

I wouldn’t put something in my engine that can’t handle cold weather. Of course, I don’t use any oil additives, the oil already comes with all the additives needed.