5w20 5w30 blend GM 3.1L

[buickman50401]

I needed to change the oil in my 3.1L Buick the last weekend and had 2qts of Pennzoil Conventional 5w20 orphaned on my shelf so I decided to "get rid of them" and use them in this oil change for the Buick which normally calls for 4.5qts of 5w30.

Right now its running 2.5qt 5w30 and 2qt 5w20 (both Pennzoil conventional). Using the online calculator it looks to work out roughly to 9.49cSt @ 100deg making it a very heavy 20 or very light 30wt.

Impression so far? Better cold starting (we've been hovering around 0deg here for a few weeks). Its also silenced (not just reduced) the valve/lifter clatter common in most 3.1L GMs.

Gas mileage seems to have also been marginally improved though I will of course track it closely over this OCI to compare against past records.

I plan on running a used oil analysis and depending on how things look, the Buick might be going to 3 qts 5w20 or a full 4.5qts in the future.

 

[charbaby]

The only thing you can do is experiment! I don't think you'll have any issues and this may turn out to be your new oil(s) of choice.

 

[daman]

These engines will easily take 5qts stop messing with that 1/2 qt stuff. I've been doing it for decades.

 

[jstutz]

No issues running your blend in this engine. Its not all that different than some really thin 30 weights. We have been using 5w20 in many of our family's 3.1 and 3.8s in the winter and it seems to do fine. I guess its hard to tell what 300K miles down the road will bring though. I think the difference between 5w20 and 5w30 is small and will only be noticed toward the end of an engines lifespan. I think there are a lot of other factors that get neglected such as air filters, air leaks, coolant leaks, fuel dilution ect. that greatly reduce an engines lifespan. The difference between the worst 5w20 and best 10w30 is probably not as significant as what i listed above. This is just my thought and of course it depends on your engine but im assuming some stand "easy on oil engine".

 

[demarpaint]

Originally Posted By: jstutz
No issues running your blend in this engine. Its not all that different than some really thin 30 weights. We have been using 5w20 in many of our family's 3.1 and 3.8s in the winter and it seems to do fine. I guess its hard to tell what 300K miles down the road will bring though. I think the difference between 5w20 and 5w30 is small and will only be noticed toward the end of an engines lifespan. I think there are a lot of other factors that get neglected such as air filters, air leaks, coolant leaks, fuel dilution ect. that greatly reduce an engines lifespan. The difference between the worst 5w20 and best 10w30 is probably not as significant as what i listed above. This is just my thought and of course it depends on your engine but im assuming some stand "easy on oil engine".


I agree.

This is a good comment: QUOTE "I think the difference between 5w20 and 5w30 is small and will only be noticed toward the end of an engines lifespan." There's a good chance the 20 grade oil might even extend the life "slightly". Proving it one way or another would be very difficult. JMO

 

[buickman50401]

Originally Posted By: jstutz
No issues running your blend in this engine. Its not all that different than some really thin 30 weights. We have been using 5w20 in many of our family's 3.1 and 3.8s in the winter and it seems to do fine. I guess its hard to tell what 300K miles down the road will bring though. I think the difference between 5w20 and 5w30 is small and will only be noticed toward the end of an engines lifespan. I think there are a lot of other factors that get neglected such as air filters, air leaks, coolant leaks, fuel dilution ect. that greatly reduce an engines lifespan. The difference between the worst 5w20 and best 10w30 is probably not as significant as what i listed above. This is just my thought and of course it depends on your engine but im assuming some stand "easy on oil engine".


Good to hear you've had decent luck with 5w20 in this engine.

I'm not too concerned about making it to 300k mi. The car is a '03 with 117k on it. The engine let loose at 105k - leaky injector lead to fuel "washdown" of #5cyl and some nice bare metal on metal contact. There was concern about lower end damage as well (mains).

Had a remanned unit dropped in for only $400 more than it would have cost to have the head replaced and the bottom end torn apart and inspected.

So this engine only has about 12k mi on it and the transmission and body are going to go long before the new engine ever does. I plan on keeping it for the next 3 years (5 tops) and then getting rid of it so if 5w20 works then I'm going full 5w20 in the future and no blend.

 

[jstutz]

Originally Posted By: buickman50401
Originally Posted By: jstutz
No issues running your blend in this engine. Its not all that different than some really thin 30 weights. We have been using 5w20 in many of our family's 3.1 and 3.8s in the winter and it seems to do fine. I guess its hard to tell what 300K miles down the road will bring though. I think the difference between 5w20 and 5w30 is small and will only be noticed toward the end of an engines lifespan. I think there are a lot of other factors that get neglected such as air filters, air leaks, coolant leaks, fuel dilution ect. that greatly reduce an engines lifespan. The difference between the worst 5w20 and best 10w30 is probably not as significant as what i listed above. This is just my thought and of course it depends on your engine but im assuming some stand "easy on oil engine".


Good to hear you've had decent luck with 5w20 in this engine.

I'm not too concerned about making it to 300k mi. The car is a '03 with 117k on it. The engine let loose at 105k - leaky injector lead to fuel "washdown" of #5cyl and some nice bare metal on metal contact. There was concern about lower end damage as well (mains).

Had a remanned unit dropped in for only $400 more than it would have cost to have the head replaced and the bottom end torn apart and inspected.

So this engine only has about 12k mi on it and the transmission and body are going to go long before the new engine ever does. I plan on keeping it for the next 3 years (5 tops) and then getting rid of it so if 5w20 works then I'm going full 5w20 in the future and no blend.


Very good, remember that the conditions i use the 5w20 in with the 3.1 is winter with short trips and driven easy. If your racing it or something results could be different. My moms has terrible piston slap when it is cold. So far im not convinced anything has helped it. It makes me wonder if it is a injector. It stops withing 30 seconds or so.

 

[buickman50401]

Originally Posted By: jstutz

Very good, remember that the conditions i use the 5w20 in with the 3.1 is winter with short trips and driven easy. If your racing it or something results could be different. My moms has terrible piston slap when it is cold. So far im not convinced anything has helped it. It makes me wonder if it is a injector. It stops withing 30 seconds or so.


Nothing will help the piston slap short of new pistons and cleaning up the cylinder bore. The reason the slap stops after 30 seconds (or at least reduced to an imperceptible level) is that the piston has expanded enough to reduce most of the excess clearance in the bore.

Quote:

In the case of the famous GM piston slap engine defect, the piston design with hypereutectic (high silicon content aluminum alloy) pistons, reduced or eliminated piston skirts (to reduce reciprocating mass), and a higher ring pack to reduce unburned fuel mixture on the sides of the piston crown have made piston to cylinder bore fit much more critical.