Decisions, decisions. Pontiac 3.4L.

[mrdctaylor]

Yeh, it is another "what oil should I use" thread. I'm looking for recommendations because I am torn between a few options. Perhaps I've read TOO much on this board.

I have a 1997 Pontiac Trans Sport with the 3.4L V6. Up until about 60K miles, I used whatever conventional 10w30 oil the dealer happened to use. At that point, I did an AMSOIL engine flush and began using AMSOIL 10W30. At 70K I began using AMSOIL 5W30 for no particular reason. I usually change my oil about every 6 months which comes to about 7K miles.

I am now at 87K miles and will be doing an oil change in a month or two and I've begun thinking about whether or not to order more AMSOIL. I use Mobil 1 5W30 in my relatively new Toyota Tacoma because it is under warranty and I want to use an API certified oil (I know, I know...). Since I'm already buying oil locally for my other vehicle, I'm thinking of buying something local for my Pontiac as well.

Anyway, I'm trying to decide the following:
1) At this point, is there any issue with putting a thinner synthetic (i.e. Mobil 1) in the engine?
2) Is there a big different between Mobil 1 10W and 5W30? I don't mind buying 10W, but I guess it would be ideal to use the same oil in both vehicles, and I am set on using 5W30 in my Toyota for now. Would Mobil 1 5W40 offer any added benefit in this engine?
3) I know I could try GC, but I guess I want to make sure I can find the oil when I need it. GC always seems to be in short supply.
4) I could always order AMSOIL again, but I'm wondering if it is worth the extra expense if I'm changing at 6 months and not going an entire year. With Wal-Mart selling 5 qt judgs of Mobil 1 for under $20, AMSOIL looks more pricey than it used to.

I guess I'm just looking for opinions. I guess I'm leaning towards Mobil 1 of some variety just because it is relatively cheap and available locally. But I've had good experiences with AMSOIL too.

 

[JohnnyO]

Being in Texas in the summer, I think the Mobil 1 10w30 would be fine. Maybe all year. My opinion is that the 10w M1 is somewhat better than the 5w but both are great oils for the money.

 

[edvanp]

I have a 3.4l in a Montana. I've had very good luck with 5w & 10w M1 Synthetics. Prior to this last change, I ran Havoline 5w40 syn & found the vehicle to be a bit less peppy. When I changed the oil and went back to 5w30 (Valvoline-syn this time), it ran better. I did a 6k mile trip a few summers ago out west and it ran great on M10w30.

 

[haley10]

Consumption with Mobil 1 10w30 will be less than with the 5w30. The 10w30 is a better choice.

The choice between Mobil 1 10w30 and Amsoil ATM is a tough one.

ATM is more expensive, but you will require less makeup and it can go somewhat longer.

Wally's jugs may make it too hard to pass up. I think you might get enough out of ATM to make it a wash. Up to you.

 

[jthorner]

The big risk with the GM 3.4L is intake manifold gasket leaks which let coolant into the oil.

Far more important than what oil brand you run is to do an oil analysis at least twice per year and catch the signs of coolant early. It will show up as potassium and sodium elevation in oil analysis long before showing up as water and antifreeze. Catch it early and there will not be much damage. Catch it late and the engine needs complete rebuilding. Both GM vans we have owned, a '98 and and '02 have had the leak at between 40-50k miles.

Given this situation with this engine, frequent changes to flush out contaminants are much better insurance than anything else.

Extended drains on an engine which has a design propensity for mixing coolant into the oil is a bad idea.

To your original question, Amsoil is IMO a waste of money.

John

 

[pooter WS6]

I think the 3.4 that was natorious for intake leaks was the 3.4 DOHC. Not the pushrod version. I have owned a Z-34 with the 3.4 and at 98,000 miles, the intake began to leak. The 3.4 pushrod engine is a 90 degree engine derived from the infamous 3.1L chevy engine. If anyone has had leaks in the intake gaskets, it had to be a surface flatness issue at the plant.

 

[crashz]

Its a tough choice between Mobil 1 10w30 and Amsoil's ATM. Both are excellent oils and in my opinion, almost equivalent. Mobil 1 definately has the price & availibility advantage, but ATM is a bit thicker and will quiet down your engine (some people complain of more engine noise with Mobil 1). If you become a preffered customer of Amsoil, the pricing gap closes considerably and becomes worth while.

 

[mrdctaylor]

Thanks for the replies. A few comments:

1) This oil change that I do in a month or two will take me through the winter. I'm assuming running Mobil 1 10W30 in Texas winters (only gets to maybe 20* at the coldest, and not even that cold for long) is ok. I ran conventional 10w30 for years, so I guess I shouldn't be too concerned.

2) Good point about the intake manifold leak. I had it fixed last year! Luckily, they had just redesigned the gasket and changed the torque specs on it to (hopefully) keep it from happening again. I keep a very close eye on the coolant level now.

3) As for consumption, it doesn't use any oil as far as I can tell when using AMSOIL 5W or 10W30. Hopefully this will still be the case with the slightly thinner Mobil 1. We shall see.

I was leaning towards Mobil 1 10W30 anyway, and I think that's what I'll probably do. Thanks for the input.

 

[tmorris1]

I have a used oil analysis posted for my 1998 TranSport Montana using Mobil 1 5W30 and it did great for me. I have never had any consumtion issues with Mobil 1 in this engine. The oil is at the full mark whenever I change the oil. This summer I am running Mobil 1 10w30 for the first time, but will switch back to 5W30 for winter.

quote:

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I think the 3.4 that was natorious for intake leaks was the 3.4 DOHC

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This could be true, but the 3.1 and 3.4 pushrod motors are just as bad or worse. I have owned a 3.1 along with some friends who have and never had problems with them. I now own a 3.4 and know 2 other people that have 3.4 pushrods, and we all have had the manifold leaks.

 

[Al]

quote:

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Originally posted by jthorner:
The big risk with the GM 3.4L is intake manifold gasket leaks which let coolant into the oil.

Far more important than what oil brand you run is to do an oil analysis at least twice per year and catch the signs of coolant early. It will show up as potassium and sodium elevation in oil analysis long before showing up as water and antifreeze. Catch it early and there will not be much damage. Catch it late and the engine needs complete rebuilding. Both GM vans we have owned, a '98 and and '02 have had the leak at between 40-50k miles.

Given this situation with this engine, frequent changes to flush out contaminants are much better insurance than anything else.

Extended drains on an engine which has a design propensity for mixing coolant into the oil is a bad idea.

To your original question, Amsoil is IMO a waste of money.

John

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Ding..ding..ding.. The man has it right.Shorter OCI and analysis on this puppy. The odds of this pos making it to 100K without the intake manifold blowing are about zero-seriously.

Opps-fixed..I say the 10w30 and you could put a quart of the 15W-50 in Texas.

 

[MAJA]

I am in a similar situation. I was using Amsoil in a 2000 GMC Sonoma. I just started the rinse phase of the Auto RX treatment with conventional oil, but am debating what to use after the rinse is over. Reading this board, along with my relatively short oci's, has convinced me to switch to Delvac 1300 15w40 on all my other vehicles and tractors.
I was not getting enough value out of the Amsoil oil, having to also pay for shipping. As for the Sonoma, I am debating about buying Mobil 1 10w30 over the counter, or using the Delvac 1300. I am sure I will not go back to Amsoil, unless the prices, which includes shipping, become more inline with buying over the counter.