Am I using the wrong weight oil

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Reishi

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I have a '94 Chevy 1/2 c1500 2 wheel drive. It has 155,000 miles on it. I have owned the vehicle for about for years but I have always gotten horrible mileage, usually 10-12 miles per gallon at best. Well, when I bought the truck the guy at autozone told me to just use 10w-40 in it so that is what I have been using for 3 years now. However,the vehicle actually calls for 5w30. He claimed that any time an engine gets 100,000 miles on you are just suppose to go on up to 10w-40 regardless of what it calls for due to internal wear and since I had never owned a truck with a lot of mileage on it I just took his word

Should I drop it back down to what it actually calls for and do you think that using the wrong weight oil might actually account part of the poor mileage I get. I am thinking about using some Auto-rx but I want to know if I should use it in 5-30 or 10-40

Thanks for the help,
Reishi
 
Oil will not make a whole lot of difference in the m.p.g.s " The Auto r/x works well in freeing the rings up I use it. Do a 2 treatment clean following the instructions .
 
What about engine wear. Does it require a thicker oil?

I live in the South where the average winter temp is 45 at its lowest and 105 during the summer.
 
Old style v8 Chevy with warmer than average temperatures? 15 years old?
10-40 is fine. Get your gas mileage elsewhere.
[And I normally like thinner oils.]
 
Because of the higher mileage on this vehicle I would suggest
one of the high mileage oils in 10w30 as a starting point.
see how it goes and adjust from there if you need to. Good luck

SS
 
Quote:
Well, when I bought the truck the guy at autozone told me to just use 10w-40 in it so that is what I have been using for 3 years now.


You've been using 10W-40 for 3 years and the engine is still running?!!?
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Yeah, but I have been getting poor mileage for three years and was wondering if there was any coralation between using an oil that is too thick and below Mfg. mileage
 
The oil may not be doing what you want. At that mileage Auto-Rx may free up the rings and remove enough sludge to make a meaningful difference in performance and economy. I had a V-8 Caddy that changed its personality and operating cost once it was cleaned out. Hopefully yours too! After that, a good 10w30 works great. Or a 10w40 if you prefer.
 
Reishi,

Merkava_4 is being sarcastic...there is nothing wrong with 10W-40, especially for an older, high-mileage chev V-8...sounds like a good choice to me.

There's way, way, way too much 'anti 10W-40' paranoia on this site.....
 
I went ahead and changed my oil today and went with Castrol GTX 10-30. I will see how that does for a bit and go from there. I have always associated thinner oils with smaller engines but I know that that assumption is very ignorant on my part which is why I decide to actually post on this forum instead of just lurking like I have been doing for a year now.

I am noticing more noise with the 10-30 but I don't necessarily think that it is coming from the engine itself but more than likely something else completely coincidental.

I plan on getting the Auto-rx but I need to pick up another pay check before I can purchase it. I don't remember it being that expensive when I first started looking at this board a year or so ago. I thought it was closer to 15 bucks a bottle. However, if it lives up to its name ( which I am sure it will) then it will be money well spent. I plan on doing a compression check this weekend and replacing the valve cover gaskets since one of mine appears to be leaking a bit. This will give me a chance to get a good before picture of whats on the inside of this beast.

Thanks for all your help. I am just concerned that if the engine is used to 10-40 that 10-30 is going to cause some unforeseen problems down the road. If I don't notice any improvement in performance or efficiency then I will probably go back to 10-40 since it offers better protection. Or does it? The more I think about it the less I understand. lol
 
If I had known you were going to change your oil so soon after starting this thread, I would've advised you to stay with the 10W-40 since the engine has probably worn into it.
 
I had a mechanic tell me to use a 10w30 oil instead of a 5w30 when my Aerostar reached 100K miles. I have close to 160K on it now and still use 5w30 + 6oz VSOT. I am adding a little less than 1/2 qt of oil during my 3000 mile oil change intervals. I figure if that make up oil goes to 1 qt per OC interval I'll give the 10w30 a try.

Is there anything wrong with this Logic?

Thanks,
Frank D
 
Reishi, what size engine do you have? I've got a '90 model Chevy pickup with a 5.7 (350) engine...last highway trip I got 20.5 mpg just after installing a 70 series Flowmaster (2 in 2 out) with 2 1/4 inch dual exhausts (no cat), motor oil was 10w30 Amsoil ... prior to that, my best mileage was 18.3 mpg with regular tube type glass packs with 2 inch exhaust pipes (no cat). I use regular 87 octane fuel and sometimes add some Lucas fuel treatment - just got some Marvel Mystery Oil and will try a little of that.

Last check around town was 16.5 mpg with a little Lucas in the gas. I'm presently using 5w30 SuperTech Synthetic motor oil since it is now rarely driven and the engine runs smooth with 120K on the clock. Rear end gear lube is Amsoil as well as the ATF fluid. Keep a check on your tire pressure. You might want to try some dual exhausts?? I also have an Amsoil foam type air filter with the top of my breather flipped - don't know if that really helps anything or not...but if you have to "get on it" when passing it sure sounds good! I try to keep the "Chattanooga" Chevy well maintained as it belonged to my late Father.
 
Hey pig,

I have a 94 chevy c-1500 (silverado) .5 ton 2 wheel drive with the V-e 350 with the 5.7 liter displacement with the throttle body. I have upwards of 170,000 miles and it has never gotten more than 13 miles per gallon at best. That is without the A/C running. If I turn it on my mileage drops down to about 11.
I currently have dual flowmasters but with a cat and it is the one in 2 out style. I am using the Amsoil in the Rear end and recently had to have my transmission dropped at my uncles shop to replace a solenoid and while it was down we flushed the transmission, replaced the filter and went back with Amsoil ATF. Also I am using a K and N Air filter. Right now I have Castrol GTX 10-30 in the engine because I needed a dino oil for the auto-rx.

I am really at a loss as to why my mileage is so poor since almost all of our other stats are similar. I just purchased 2 bottles of auto-rx and I am really hoping that it works some magic but I recently had to replace my valve cover gaskets and I didn't really see much sludge at all. Is it uncommon to have relatively clean valve covers and still have enough build up inside the engine to effect the mileage this much?

I mean, aside from the mileage issue this has been a great truck. It is more powerful that I will ever need it for. Very responsive. Like I say, the only downfall is the fuel economy. It is killing me here.

Any help regarding improvement in the fuel economy is greatly appreciated.

Reishi
 
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