One more good fail pic from my shop

And an STP sticker...

MM

Lol!
I still use STP in my kids cars, the Corvette, GTO, and the 3.0 Mercruiser in my kids boat. Used it in the motors in my old boat too. Basically, anything that isn’t leased or the diesels in my current boat get it at every oil change.
 
Lol!
I still use STP in my kids cars, the Corvette, GTO, and the 3.0 Mercruiser in my kids boat. Used it in the motors in my old boat too. Basically, anything that isn’t leased or the diesels in my current boat get it at every oil change.
IMG_2098.JPG

What does STP do that a high quality oil changed at manufacturers' recommended intervals can not do?
 
View attachment 62822
What does STP do that a high quality oil changed at manufacturers' recommended intervals can not do?

Adds back in the ZDDP that the feds had removed from automotive motor oil, and leaves a nice coating on bearing surfaces that is good to have for cold starts after sitting for long periods of time.
My Corvette and GTO only see about 1000 miles a year, the kids cars sit around a lot when they are away at school, and the 3.0 Mercruiser in the little boat also sits for long periods of time.
 
Adds back in the ZDDP that the feds had removed from automotive motor oil, and leaves a nice coating on bearing surfaces that is good to have for cold starts after sitting for long periods of time.
My Corvette and GTO only see about 1000 miles a year, the kids cars sit around a lot when they are away at school, and the 3.0 Mercruiser in the little boat also sits for long periods of time.

Has it been removed from marine oils?

MM
 
Have been using Merc blend oil.

MM

Hmmm... good question...
Not sure if the removal extended to oil that is typically used off road. You could probably contact them to find out.
Either way, I don’t think adding the STP could hurt anything even if the Merc blend oil you’re using still has the ZDDP in it.
If anything, aside from the ZDDP, the STP itself leaves a nice film on internal surfaces to reduce wear.
I like to think that is particularly good in engines that can sit a long while without being run like in boats or cars that aren’t used regularly.
I can remember pulling the distributors and valve covers on motors that sat for a long time so we could spin the oil pumps and get oil on all the surfaces before trying to start them dry.
While most boat and even collector cars don’t typically sit long enough to have to do that, it’s kind of the same school of thought.
Some may argue that it is either snake oil, or otherwise unnecessary, but I get it these days at Walmart for under $3.00 a bottle where I also buy most of my motor oil. Since I do the oil changes myself, and I’m not paying someone else to do them, I don’t mind spending the extra $3.00 to try to avoid some engine wear.
 
Hmmm... good question...
Not sure if the removal extended to oil that is typically used off road. You could probably contact them to find out.
Either way, I don’t think adding the STP could hurt anything even if the Merc blend oil you’re using still has the ZDDP in it.
If anything, aside from the ZDDP, the STP itself leaves a nice film on internal surfaces to reduce wear.
I like to think that is particularly good in engines that can sit a long while without being run like in boats or cars that aren’t used regularly.
I can remember pulling the distributors and valve covers on motors that sat for a long time so we could spin the oil pumps and get oil on all the surfaces before trying to start them dry.
While most boat and even collector cars don’t typically sit long enough to have to do that, it’s kind of the same school of thought.
Some may argue that it is either snake oil, or otherwise unnecessary, but I get it these days at Walmart for under $3.00 a bottle where I also buy most of my motor oil. Since I do the oil changes myself, and I’m not paying someone else to do them, I don’t mind spending the extra $3.00 to try to avoid some engine wear.

Good post!

MM
 
IMG_2098.JPG
Just read up on this a little. STP replaces the zinc and phosphorus that was removed from modern motor oils because those elements bind with catyletic converter components and shorten the life of the converters. Modern synthetic oils offer superior wear protection through other means in modern engines making the zinc and phosphorus unnecessary. 60's muscle cars and hot rods with modified high performance racing engines and flat tappets apparently require zinc and phosphorus to minimize wear. There are oils available that meet the special needs of these engines. STP would seem to be useful when used in those types of circumstances. You should probably avoid using it in boats that have catylitic converter technology.
 
Last edited:
View attachment 62981 Just read up on this a little. STP replaces the zinc and phosphorus that was removed from modern motor oils because those elements bind with catyletic converter components and shorten the life of the converters. Modern synthetic oils offer superior wear protection through other means in modern engines making the zinc and phosphorus unnecessary. 60's muscle cars and hot rods with modified high performance racing engines and flat tappets apparently require zinc and phosphorus to minimize wear. There are oils available that meet the special needs of these engines. STP would seem to be useful when used in those types of circumstances. You should probably avoid using it in boats that have catylitic converter technology.

Good point.
Probably why they make another formula for use with synthetic oil that doesn’t mention Zinc.
 

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