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#3448801 - 08/07/14 12:02 PM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: that_guy318]
KCJeep Offline


Registered: 06/30/11
Posts: 4573
Loc: Mahzurrah!
Blue bottle STP does have zinc, but less than the motor oil you are adding it to. It is primarily an oil thickener. I still have a soft spot for it though. No oil change was complete without a can of STP when I was a teen. Have used it in the Jeep fairly recently and it did seem to like it, the Jeep does favor thicker oils though.

Great UOA I wouldn't change a thing it's obviously working for you.
_________________________
2004 Jeep GC WJ 4.0 @ 122k Pennzoil HM 10w30 w/MoS2
Napa Silver 31515
KIA Sedona 39k, Chevy Lumina 173k, Chrysler Sebring 171k, Ford Ranger 176k!

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#3449215 - 08/07/14 08:15 PM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: that_guy318]
that_guy318 Offline


Registered: 08/04/14
Posts: 11
Loc: PA and SC
I think my engine likes the thicker oil too. I have right under 40lbs of pressure at idle and right under 60 or so at cruising speed.
_________________________
-99 Durango 5.2L V8 168k miles
Castrol GTX High Mileage 10w30 with Purolator/Mopar filter every ~3,500 miles

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#3449401 - 08/08/14 02:47 AM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: that_guy318]
Garak Offline


Registered: 12/05/09
Posts: 11459
Loc: Regina, Saskatchewan, Canada
Originally Posted By: that_guy318
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.

Somewhere in the VOA section, I did the calculations to show that regular STP will actually dilute the zinc content of most motor oils. It's worse than useless as a ZDDP additive.
_________________________
Plain, simple Garak.

2008 Infiniti G37 coupe - Mobil Delvac 1 ESP 5w-40, Hastings LF113
1984 F-150 4.9L six - Quaker State GB 10w-30, Wix 51515

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#3451974 - 08/10/14 09:42 PM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: Garak]
that_guy318 Offline


Registered: 08/04/14
Posts: 11
Loc: PA and SC
Originally Posted By: Garak
Originally Posted By: that_guy318
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.

Somewhere in the VOA section, I did the calculations to show that regular STP will actually dilute the zinc content of most motor oils. It's worse than useless as a ZDDP additive.


It looks like it increased the zinc content of my oil though. http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1414695
_________________________
-99 Durango 5.2L V8 168k miles
Castrol GTX High Mileage 10w30 with Purolator/Mopar filter every ~3,500 miles

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#3452063 - 08/11/14 01:31 AM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: that_guy318]
Garak Offline


Registered: 12/05/09
Posts: 11459
Loc: Regina, Saskatchewan, Canada
Perhaps, if the original ZDDP content was low enough, of course. For most oils, it's certainly not true.
_________________________
Plain, simple Garak.

2008 Infiniti G37 coupe - Mobil Delvac 1 ESP 5w-40, Hastings LF113
1984 F-150 4.9L six - Quaker State GB 10w-30, Wix 51515

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#3457997 - 08/17/14 01:16 PM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: that_guy318]
2KBMW Offline


Registered: 10/29/03
Posts: 464
Loc: Ontario Canada
[quote=that_guy318]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 ?

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#3458355 - 08/18/14 12:14 AM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: 2KBMW]
that_guy318 Offline


Registered: 08/04/14
Posts: 11
Loc: PA and SC
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.
_________________________
-99 Durango 5.2L V8 168k miles
Castrol GTX High Mileage 10w30 with Purolator/Mopar filter every ~3,500 miles

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#3459086 - 08/18/14 09:03 PM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: 2KBMW]
artificialist Offline


Registered: 09/23/07
Posts: 6798
Loc: Florida
Originally Posted By: 2KBMW
[quote=that_guy318]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.
_________________________
2010 Lancer Ralliart Sportback

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#3470772 - 09/01/14 11:18 AM Re: Castrol GTX HM 10w30 +STP/3,300mi/99 Durango 5.2 [Re: artificialist]
that_guy318 Offline


Registered: 08/04/14
Posts: 11
Loc: PA and SC
Originally Posted By: artificialist
Originally Posted By: 2KBMW
[quote=that_guy318]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.
_________________________
-99 Durango 5.2L V8 168k miles
Castrol GTX High Mileage 10w30 with Purolator/Mopar filter every ~3,500 miles

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