27 year old GMC Sierra 93,000 miles. Should I switch to full synthetic(Mobil 1)?

[Chris B.]

Hey everyone! I have a nearly 27 year old Sierra with the first gen 5.7 Vortec. It only has 93,000 original miles and has seen mostly Castrol GTX 5w30 through out it's life. Blackstone Labs UOA's have shown good wear results over the years. It currently has no oil leaks and burns no oil. I'm thinking of switching it to Mobil 1 High Mileage to help keep seals in good shape as it gets older and to help with faster lubrication on cold start ups after sitting for months and also sub zero winter start ups. Any concerns that the full syn oil could cause oil burning and leaks? Should I stay with Castrol GTX 5w30 or do you think the Mobil 1 High Mileage 5w30 would be good for it at this point in it's life? Truck is garaged and only sees 1,000 miles a year these days. Napa Gold oil and air filters used. I really want the best for this truck and money for oil is of no concern. What do you oil experts advise? Here is a couple pictures of the truck:

 

[PontiacHO]

Others will weigh in regarding the change in oils. That’s a beautiful truck. You asked so…I’d stick with exactly what’s been used. It’s working.

 

[demarpaint]

Nice truck! I don't see any downside using the Mobil 1 HM oil you mentioned. Some might say making the change can/might cause leaks, I don't think you'll have any problems.

 

[doublebase]

I mean, give it a try, it’s not going to hurt anything. It may leak a bit, but maybe not. Not sure I’d do it because of the high mileage oil and gaskets...I don’t think that’s going to help much.

 

[AutoMechanic]

Personally I think what your running is fine but I don’t think it would hurt to use the Mobil 1 either.

 

[SC Maintenance]

Nice truck.

I am not an expert. However I still run conventional or a semi syn in my 392K mile Xterra, simply because I always have. If it aint broke,....

IMH (non expert) O.

 

[joekingcorvette]

Nice truck and I like the chrome wheels too. Use either oil but if it were mine I would switch to the HM Mobile 1.

 

[KrisZ]

Sweet looking truck.
Not sure I would mess with the oil on it though.

 

[CharBaby]

If you have only used conventional oils all of the vehicles life and with almost 100,000 miles, I wouldn't change anything. Keep in mind that todays conventional oils are actually a synthetic blend(even of the label doesn't say...syn/blend). I have put on several hundred thousand miles on engines with conventional oils even before the oils were Group II/III

However, most synthetic oils that we can buy today are of a Group III conventional oils, which are then Hydro-processed to a synthetic standard. Meaning(if I am saying this correctly), the oil is refined & processed which is contributing to the chain molecules rivaling Group IV(PAO) synthetics along with a better(more robust) additive package. These Group III synthetic oils may even be better than FULL SYNTHETIC(lab created) oils of decades ago.

If you can buy synthetic oils at a reasonable price(I do) then have at it!

Again, if I said that right!

Oh yeah, nice truck!

 

[billt460]

Hey everyone! I have a nearly 27 year old Sierra with the first gen 5.7 Vortec. It only has 93,000 original miles and has seen mostly Castrol GTX 5w30 through out it's life. Blackstone Labs UOA's have shown good wear results over the years. It currently has no oil leaks and burns no oil. I'm thinking of switching it to Mobil 1 High Mileage to help keep seals in good shape as it gets older and to help with faster lubrication on cold start ups.......

That's what I did with my 1991 F-150. I ran mostly Castrol 10W-40 Dino oil for the first 125,000 miles with religious oil and filter changes. Then I switched to Mobil 1 High Mileage 10W-40. And I have been running that ever since.

I had a leaking rear main, and the Mobil 1 High Mileage really helped in cutting down on the leaking. It still leaks, but it's getting less and less with every oil change. It leaked profusely with the Castrol Dino oil.

Great looking truck by the way!!

 

[ka9mnx]

When I bought my '93 F150 used in 2003 with 160k miles it was immediately changed to synthetic (?) oil. Now, 20 years later and at 258k miles and still using synthetic, I've seen no downside. Also, I wouldn't bother with HM oil.

Long story short, either oil will work for you.

 

[wlk]

Nice truck. For the age yes I'd go HM in either oils, I do in my 93 C1500. If you tow I'd go up to a 5/10w40 in it but keep it changed and the motor will outlast the truck

 

[DavidJones]

My guess is the truck won't know the difference.

 

[Revving2Redline]

I wish I could recommend Castrol magnatec to you but it's gone. maybe for a couple of oil changes use the green bottle of Castrol HM and then go full synthetic hm. I think if you get any leaks it will be from gm infinite wisdom for cork gaskets like on my Pontiac Grand Prix W body 90s. Id sure go up to mobil 1 10w30 HM. How often do you drain and fill your transmission fluid?

 

[Triple_Se7en]

If it's not weeping or leaking, then I would stick with a semi-synthetic. Even if / when it begins to show a drop of oil (or three) on the concrete below the truck, I'd introduce that beauty to a semi-synthetic like Valvoline Maxlife.

 

[TomYoung]

You have run Castrol GTX, but that is now a synthetic, right. I would run the new Castrol GTX full syn all day long. Congrats on a very well maintained vehicle, with "barely broken in" mileage. The fact is that any synthetic will serve you well. With conventional and blends, you gotta watch the shelf closely.

 

[Malo83]

Others will weigh in regarding the change in oils. That’s a beautiful truck. You asked so…I’d stick with exactly what’s been used. It’s working.

x2.

 

[Chris B.]

That's what I did with my 1991 F-150. I ran mostly Castrol 10W-40 Dino oil for the first 125,000 miles with religious oil and filter changes. Then I switched to Mobil 1 High Mileage 10W-40. And I have been running that ever since.

I had a leaking rear main, and the Mobil 1 High Mileage really helped in cutting down on the leaking. It still leaks, but it's getting less and less with every oil change. It leaked profusely with the Castrol Dino oil.

Great looking truck by the way!!

Beautiful Ford!!! Did you ever do a UOA to see how the oil protected against wear?

 

[Chris B.]

When I bought my '93 F150 used in 2003 with 160k miles it was immediately changed to synthetic (?) oil. Now, 20 years later and at 258k miles and still using synthetic, I've seen no downside. Also, I wouldn't bother with HM oil.

Long story short, either oil will work for you.

Why not bother with the Hight Mileage oil? Thanks!

 

[Chris B.]

You have run Castrol GTX, but that is now a synthetic, right. I would run the new Castrol GTX full syn all day long. Congrats on a very well maintained vehicle, with "barely broken in" mileage. The fact is that any synthetic will serve you well. With conventional and blends, you gotta watch the shelf closely.

Thanks! I do believe the Castrol GTX is now semi-synthetic. It does say that on the bottle. What do you mean with conventional and blends you have to watch the shelf?