Valvoline VR1 Racing vs Castrol GTX Classic (20/50)

[HammerDown]

Over two decades ago I walked away from Castrol GTX Oil and religiously used Valvoline VR1 Racing 20/50 for its ZDDP levels.
Well, the Valvoline seemed to vanish from my local stores and this Castrol GTX "Classic" appeared in my local Walmart so, I purchase 16 qts.
It states it's designed for my flat tappet cam engine. I called Castrol and the rep told me it had 1400 ppm of Zinc.
Sooooo, few days ago out comes the Valvoline VR1 Racing oil and in goes the Castrol GTX Classic.
I notice coming out of the bottle the Castrol GTX Classic seems more 'sticky' or 'clingy'
Within 20 some miles with a good amount of idling I noticed my 'at Idle' psi was down to 20psi.
That NEVER EVER happened before... yes, it comes-up with RPM.
Could it be a coincidence or, was the Castrol GTX Classic 20/50 a bad choice?

 

[sunruh]

i cannot speak of the oil on the shelf today, but a few years ago i tested both Castrol GTX 20w50 and Valvoline VR1 20w50
in almost the same conditions VR1 stayed in grade and produced wonderful results.....gtx was turned in to a low 30wt
imho....friends dont let friends use gtx

my reports used to be on here...no idea if they still are after the site switch

Steve and the Mix Master of DOOM

 

[HammerDown]

i cannot speak of the oil on the shelf today, but a few years ago i tested both Castrol GTX 20w50 and Valvoline VR1 20w50
in almost the same conditions VR1 stayed in grade and produced wonderful results.....gtx was turned in to a low 30wt
imho....friends dont let friends use gtx

my reports used to be on here...no idea if they still are after the site switch

Steve and the Mix Master of DOOM

A long time ago I tried Castrol GTX 40w in my BBC Jet Boat and again showing lower oil pressures it failed miserably... I again refilled with Valvoline VR1 Racing 40w and it took the beating a marine engine dishes out.
Ugh, so now I have some 10 qts of the Castrol Classic I don't want to just toss away, maybe I'll shorted-up the change intervals to get rid of it. Or, use it in my lawn mower.

 

[sunruh]

return it to walmart with no receit

 

[HammerDown]

return it to walmart with no receit

return it to walmart with no receit

without a receipt, I hate to be one of those people but next time I'm in the store I'll ask customer service about it.

 

[OVERKILL]

Is this engine modified to require higher levels of ZDDP? A typical stock or warmed-over semi-stock style camshaft doesn't require wild levels of phosphorous, so I wouldn't get too excited about that one trait.

This GTX oil has a 100C visc of 18cSt, while the Valvoline product is heavier, at 20.5cSt, so it's not surprising you lost a bit of oil pressure. What was it at previously? I'd suspect this oil also doesn't use premium bases, since GTX is Castrol's cheapest line of oils, so it may use more VII than one might expect, and probably cheap VII prone to shear, since there are no OEM approvals to demand otherwise.