Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2

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that_guy318 said:
Yeah, it seems like the stp is working. I'm kind of surprised that there wasn't more zinc showing up on the report though. I'm going to keep using it though, it's worked for years, so why change it.

I'm also surprised that the viscosity was that low or stayed in the 30 weight range. I thought that STP raised the viscosity by two grades ie. a 30 weight oil would turn into a 50 weight. The report said it was a 40 weight though so do you think there was an error made ?
 
Originally Posted By: 2KBMW


I'm also surprised that the viscosity was that low or stayed in the 30 weight range. I thought that STP raised the viscosity by two grades ie. a 30 weight oil would turn into a 50 weight. The report said it was a 40 weight though so do you think there was an error made ?


I really don't know enough about this to say one way or the other.
 
Originally Posted By: 2KBMW
that_guy318 said:
Yeah, it seems like the stp is working. I'm kind of surprised that there wasn't more zinc showing up on the report though. I'm going to keep using it though, it's worked for years, so why change it.

I'm also surprised that the viscosity was that low or stayed in the 30 weight range. I thought that STP raised the viscosity by two grades ie. a 30 weight oil would turn into a 50 weight. The report said it was a 40 weight though so do you think there was an error made ?

Well, what ratio of STP to 10w30 engine oil? If the sump is big, the thickening effect of 1 bottle of STP might not be very big.

The second thing to consider is oil shear. How much did the 10w30 oil shear, and how much did the STP shear? Enough shearing, and an oil will go down a viscosity grade, making a 10w40 into a 10w30 and so on.

My dad told me that in the 1960s, guys used STP because they thought it was the cool thing to do. Back then, it may have made sense, due to the limited detergent content of 1960s engine oil, and because not all oils had high ZDDP.
 
Originally Posted By: artificialist
Originally Posted By: 2KBMW
that_guy318 said:
Yeah, it seems like the stp is working. I'm kind of surprised that there wasn't more zinc showing up on the report though. I'm going to keep using it though, it's worked for years, so why change it.

I'm also surprised that the viscosity was that low or stayed in the 30 weight range. I thought that STP raised the viscosity by two grades ie. a 30 weight oil would turn into a 50 weight. The report said it was a 40 weight though so do you think there was an error made ?

Well, what ratio of STP to 10w30 engine oil? If the sump is big, the thickening effect of 1 bottle of STP might not be very big.

The second thing to consider is oil shear. How much did the 10w30 oil shear, and how much did the STP shear? Enough shearing, and an oil will go down a viscosity grade, making a 10w40 into a 10w30 and so on.

My dad told me that in the 1960s, guys used STP because they thought it was the cool thing to do. Back then, it may have made sense, due to the limited detergent content of 1960s engine oil, and because not all oils had high ZDDP.


About 4.5 quarts of oil and 1 bottle (I think it's about a pint) of stp.
 
Both my 1985 Jeep Grand Wagoneers 360 and my 1993 Jeep Grand Cherokees 5.2Liter 318 recieved a bottle of STP Blue bottle at their last oil change. Glad to see others having good results with it as well. I wear my STP Teeshirt when changing oil as well!
 
Not sure if putting this in the old thread is the thing to do or not, so mods can move this if they want.

Anyway had another oil analysis done recently. Oil had been in the car for almost 6 months this time, so it got changed a bit sooner. Used Valvoline 10w30 high mileage this time along with a mopar (purolator) filter. The wear looks more or less the same to me as it did with the castrol last time.

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Also thought I'd mention that I changed the trans fluid, did a band adjustment, and replaced the radiator with one with an auxiliary external trans cooler since someone had mentioned it before.
 
Still used STP. I think only 3/4 of a bottle though. Used the other 1/4 bottle on something else. Still using the same k&n air filter too.
 
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