GM 3.4L V6?

[pbm]

If the Impala uses the 4T65E A/T, I'm surprised to hear that it's problematic. Mine has 130K w/o issue and shifts like new.
I changed out the FF ATF at 36K and again at 96K using (mostly) Mobil 1. I also add a bottle of LG red.
I consider the A/T a strong point whereas in my 01' Accord the A/T was it's achilles heel.

 

[garageman402]

The problem with the LIM seems to be the material the engine is made out of. The block is cast iron, the heads and intake manifolds are aluminum. These metals expand and contract at different rates, so mileage really doesn't mean anything, it's the number of heat/cool cycles that it's been through. Our 2000 Pontiac Montana was fixed under warranty at 60,000 miles, and we did the gaskets again at about 120,000. Engine blew up at 158,000, and was replaced with a GM Service Replacement. That engine has 40,000 on it now, and about 5 years. it's using coolant again................

 

[Hokiefyd]

Originally Posted By: garageman402
The problem with the LIM seems to be the material the engine is made out of. The block is cast iron, the heads and intake manifolds are aluminum. These metals expand and contract at different rates, so mileage really doesn't mean anything, it's the number of heat/cool cycles that it's been through.


The dissimilar metals may contribute, but I don't think they're the only factor. There are a lot of engines with iron blocks and aluminum cylinder heads, and there are even engines with iron heads with aluminum blocks, and they don't experience the same issue that these particular V-6 engines do.

Oldsmobile was using aluminum intake manifolds on their iron block/iron head engines in the 1970s. If the differing expansion rates alone caused the problems GM was experiencing with its V-6 lower intake manifolds, you'd think this would be the case with many more mixed-metal engines, right?

 

[dwcopple]

Dexcrud didn't help either

 

[Alex_V]

I've seen/worked on several with plenty of miles on them - one last week with 250K, but a lifter had bit the dust so it wasn't much longer for this world. Capable of many miles, but as stated the intake manifold gaskets should be watched if not serviced preventatively, and very sensitive to cooling system malfunctions (whether it be gaskets, water pump, etc.) that cause overheating and in such scenarios they blow head gaskets easily. Keep it maintained and it shouldn't be anywhere near done yet.

 

[garageman402]

Originally Posted By: garageman402
The problem with the LIM seems to be the material the engine is made out of. The block is cast iron, the heads and intake manifolds are aluminum. These metals expand and contract at different rates, so mileage really doesn't mean anything, it's the number of heat/cool cycles that it's been through. Our 2000 Pontiac Montana was fixed under warranty at 60,000 miles, and we did the gaskets again at about 120,000. Engine blew up at 158,000, and was replaced with a GM Service Replacement. That engine has 40,000 on it now, and about 5 years. it's using coolant again................


Hey I'm going to revive this thread again. The coolant loss I referred to was not the gasket it was a pinhole leak in the heater outlet pipe quick-connect at the back of the engine. So small the coolant would evaporate. It only leaked on a hard pull, that's how I found it.

I have heard another reason for the failures is not changing out the coolant. People think Dexcool will last 150,000 miles, but it needs to be changed out at least in 5 years, the anti-corrosion protection only lasts that long and the metal portion of the gasket is corroding.