Castrol Syntec 5w-50 yes...5w-50 Group 3 or other?

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Long story short my 277,000+ mile Civic leaks a fair amount of oil via the rear main seal....used Auto Rx a while back [rear main still leaked] ........ I'm now running Delo 400 15w-40 HDEO now with "Bars Rear main seal" which has actually slowed down the leak some. Car isn't driven much in the summer [no A/C] but the oil needs to be changed so I was going to give Auto-Rx another chance [rear main seal] but I wanted to use Castrol Syntec 5w-50 since winter isn't that far off. Car leaks very little oil when 20w-50 oil is run in it. So my logic is kill 3 birds with one stone: 50wt oil less seal leaking, 5w primary number cold starting but..... I just need to know if this oil is Group 3 or not. Thanks, Glen
 
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According to Castrol, it is GP III. I used it for two years in a Toyota pickup and my wife's little Chrysler. Both were 4 cyl. I did not develop any love for it and was about to go back to conventional until I tried another brand of synthetic and have stayed with that brand. This was some time back and it may be better now. I actually never did a UOA, but, I think it sheared much and fast. Engines started to sound different, mechanical noise around 2000 miles. One of those engines I am still running today with a 15W-50 oil and it runs great.
 
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To get that spread, a 5W-50 oil is never JUST group III. It is a mix of III, IV, and V. It's a very good oil, but not what you want to use with Auto-Rx. Best results with convetional; 15W-40 would work well.
 
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 Originally Posted By: FrankN4
According to Castrol, it is GP III. I used it for two years in a Toyota pickup and my wife's little Chrysler. Both were 4 cyl. I did not develop any love for it and was about to go back to conventional until I tried another brand of synthetic and have stayed with that brand. This was some time back and it may be better now. I actually never did a UOA, but, I think it sheared much and fast. Engines started to sound different, mechanical noise around 2000 miles. One of those engines I am still running today with a 15W-50 oil and it runs great.
Long ago, well before I joined here in 2004, I read that the Castrol 5w-50 is heavily dosed with VIIs. That would make sense, given the wide vis spread, and the probable composition of the base oil. That would tend to support Frank's observations, which are consistent with shearing break down of the VIIs. More alarming is what those degraded VIIs might be doing in the oil after their degradation. I have also heard comments to this effect here on BITOG, but quite frankly, never had any cause to dig into the issue.
 
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There have been a couple of UOA's on this oil in the UOA section, and they didn't shear much at all. Very visc. stable for the spread...
 
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 Originally Posted By: addyguy
To get that spread, a 5W-50 oil is never JUST group III. It is a mix of III, IV, and V. . . .
I'm not so sure about that. There may well be small amounts of base oils other than G-III, but on the other hand, there are probably a number of different formulation strategies that would produce a marketable 5w-50. Theoretically, one approach would be reliance upon more exotic (and expensive) base fluids. Another would be a "brute force" reliance upon lots of VIIs. Unless they're using very shear stable VIIs, I'd be concerned about the latter approach for anything but relatively short OCIs.
 
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In order to meet the 5W cold viscometrics, a 5W-50 is going to use a healthy dose of PAO to meet the large viscosity spread. There is an old MSDS from ~ 2000 online …Castrol 5W-50 " …Synthetic hydrocarbons, may contain one or more of the following: 64741-51 -1 … GI 64742-54 -7 … GII or GIII 92062-09-4 … XHVI …GIII+ 151006-62 -1 … PAO 151006-63 -2 … PAO My bet would be that it is mostly PAO.
 
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What I mean is not that the stuff has NO PAO, but rather that amount used could be smaller or larger depending upon how the engineers "design" the fluid. The behavior described tends to suggest a lot of VIIs that didn't hold up in service.
 
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The last MSDS I remember seeing indicated something like 95% Highly Refined Petroleum, but, that is a little old. It could be that Syntec 5W-50 has a GP IV add rather than a GP IV base oil. I didn't even know there was such a thing as a GP IV add until a couple months ago. I couldn't find a recent UOA either, so I guess I am not much help. I tried it and I just didn't like it. I was not new to Castrol as I had been using their 20W-50 conventional for 20+ years.
 
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I wouldn't use it, I put it in my Audi one time, ran it 7,000 highway miles, it drained nasty black. I switched to Mobil 1, never looked back.
 
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 Originally Posted By: Mobil1Fan77
I wouldn't use it, I put it in my Audi one time, ran it 7,000 highway miles, it drained nasty black. I switched to Mobil 1, never looked back.
Careful there boy. You're starting to sound like a Mobil1 fan. :)
 
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I've used it in my 9-5. Seemed to do fine. It was about the only oil I've ever seen that still felt fairly thick and syrupy when hot from the engine. I have a gallon in my stash right now that I have no idea what I am going to do with.
 
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I did my version of a used oil analysis on Castrol Syntec 5w-50--- 225,000 in a Dodge Caravan, 3.3 liter v-6. Still runs good.
 

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I think I will get get a batch of this oil and run it WITHOUT Auto-Rx and be done with it already. This car is not worth much on resale anyhow and is a candidate for replacement at some point. The cost to have the main seal replaced is futile since the transmission pump could fail at any time. Then again it could just go on and on like the energizer bunny indefinitely and make it to 500,000 miles with ease. It's a great car and I have gotten more than my monies worth out of it even if I drove it to a junk yard and handed over the keys.
 
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Have you considered a 10W-40 synthetic or synthetic blend HM oil such as Mobil 1 HM or Valvoline MaxLife?
 

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 Originally Posted By: FrankN4
Have you considered a 10W-40 synthetic or synthetic blend HM oil such as Mobil 1 HM or Valvoline MaxLife?
Yes I have. I ran Pennzoil 5w-30 HM last year with no reduction in oil consumption at all. On my last oil change before last winter I started with RTS CJ-4 5w-40. I have added so much Delo 400 15w-40 that I'm sure most of RTS has been displaced. I'm also adding Bars Leak rear main seal product and it has slowed it down to some degree. I'd consider running Mobil 1 10w-40 HM but my only reservation is winter cold flow. Maybe my concern is unfounded and it will cold flow almost as well as 5w-50 Syntec? Winter temps can get down to single digits here. The car sits for the most part during the warm months since my wife refuses to drive it because there is no A/C on this car. In the winter she gripes about the smell of oil burning when it works its way down and drips on the exhaust pipe. Is Mobil 1 10w-40 HM thicker than Delo 400 15w-40 or even Syntec 5w-50 since it's a HM oil?
 
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Some of the older BMWs run real well on the 5w50. I picked up 7 qts. for a nickle a quart. Too good to pass up.
 
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