Oil for a GM 3100 with Antifreeze leak?

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Robb235

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So the Lower Intake Manifold (LIM) gaskets have failed on my Monte Carlo with the 3100 resulting in antifreeze leaking into the crank case. These GM 60degreeV6 engines are notorious for this happening. I need to find an oil that can withstand some antifreeze dilution for a while until I can find a new motor for the car. Instead of fixing the leak, I've decided to just go ahead and replace this 3100 motor with a larger 3400 motor since I suspect the cylinder heads have warped on this current motor.

I picked up some Rotella T5 Synthetic blend oil, is this a good choice? Or should I have stayed with Valvoline Maxlife?
 
That's exactly what I would recommend - Rotella 10w30, or even 15w40 during the sumer.

You want a HDEO to protect from corrossion. Kepp changes to 2-3k miles.

Why on earth would you replace this motor with one that has the EXACT same problem? I'd put a 3800 into it - MC's came with them.
 
Just get rid of the car:problem solved.


I tend to find those years of MCs are junk anyways....


Otherwise, stick with the above.
 
Replacing the 3100 with a 3800 requires replacing the 4T60-E transmission with a 4T65-E. While the L67 (supercharged) and the L36 (non-supercharged) will physically bolt up to the 4T60-E, the PCM will not be able to control it. That, and the hassle of having to repin the C100 connector so that the 3800 engine harness will be compatible with the interior wiring harness. Another reason to use the 3400 is that 90% of the parts on the 3100 will swap over. This means I can continue to use my lifetime warranty alternator, water pump, powersteering pump, etc. I plan on tearing down the 3400 once I get ahold of it and replacing the gaskets.
 
Originally Posted By: daves87rs
Just get rid of the car:problem solved.


I tend to find those years of MCs are junk anyways....


Otherwise, stick with the above.


That is definitely my plan. These engines are a dime a dozen, so I'm only paying about ~$150 for a used engine. Once I get it fixed I plan on selling it and finding a car with an L67 supercharged motor.
 
Originally Posted By: Robb235
Replacing the 3100 with a 3800 requires replacing the 4T60-E transmission with a 4T65-E. While the L67 (supercharged) and the L36 (non-supercharged) will physically bolt up to the 4T60-E, the PCM will not be able to control it. That, and the hassle of having to repin the C100 connector so that the 3800 engine harness will be compatible with the interior wiring harness. Another reason to use the 3400 is that 90% of the parts on the 3100 will swap over. This means I can continue to use my lifetime warranty alternator, water pump, powersteering pump, etc. I plan on tearing down the 3400 once I get ahold of it and replacing the gaskets.


If you're going to the trouble of tearing down the 3400, why not re-build the 3100?

You can easily make a 3100 make the same power as a 3400......
 
I think the hdeo is a good idea, but I would want as much viscosity as possible.

Given the location and time of year, I'd go with the cheapest 20w-50 I could find, and replace it maybe every 1000-1500 miles.

I wouldn't worry about the filter, just get the oil swapped.
 
Originally Posted By: addyguy
Originally Posted By: Robb235
Replacing the 3100 with a 3800 requires replacing the 4T60-E transmission with a 4T65-E. While the L67 (supercharged) and the L36 (non-supercharged) will physically bolt up to the 4T60-E, the PCM will not be able to control it. That, and the hassle of having to repin the C100 connector so that the 3800 engine harness will be compatible with the interior wiring harness. Another reason to use the 3400 is that 90% of the parts on the 3100 will swap over. This means I can continue to use my lifetime warranty alternator, water pump, powersteering pump, etc. I plan on tearing down the 3400 once I get ahold of it and replacing the gaskets.


If you're going to the trouble of tearing down the 3400, why not re-build the 3100?

You can easily make a 3100 make the same power as a 3400......


Because I suspect that the heads are warped on my current engine, and it would be easier to find a low mileage 3400 where it's unlikely to have warped heads. Replacing LIM gaskets on a 3400 > Replacing/Machining heads + LIM change. Plus the 20hp boost from the 3100 to 3400 will be a welcome change.
 
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Originally Posted By: addyguy
That's exactly what I would recommend - Rotella 10w30, or even 15w40 during the sumer.

You want a HDEO to protect from corrossion. Kepp changes to 2-3k miles.

Why on earth would you replace this motor with one that has the EXACT same problem? I'd put a 3800 into it - MC's came with them.


Once the LIM gaskets are changed to the Fel-Pro pieces, there is no problem with this engine. Period.
 
the cheapest oil you can find. which will most likely be a HDEO 15w40 and change the oil/filter often.

If you willing to fix a 3400.. dude just fix the LIM in your 3100.

I would rather fix a LIM then fix a LIM AND swap motors.

...just read about the possibility of warped heads. Well while the LIM is off that's a prime time to pull the heads too. I still think servicing your 3100 is still the best option.

I think you can swap 3400 heads onto the 3100. don't quto me on that. But if you want specific advice I would join the 60 degree v6 forum
 
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Originally Posted By: vxcalais
Problem is the L36 and L67 3800 engines have the same issue with the leaking intake manifold gaskets. Have changed them on both engines already.

Like the 3.1, there is no problem with the 3.8, but only after you put the Fel-Pro intake set on. Both are excellent engines capable of going 250K+. Unless it's already been done, I'd consider this the first step after purchasing any vehicle with either of these engines.
 
Originally Posted By: labman
How about the cheapest stuff on sale and change it often?


This is exactly what I do on our Windstar that does the same thing. Why waste your money on a good oil, when you need to change it more often anyway?

It's the concentration of coolant in your oil that damages bearings..I need to change it every 2,600 miles or less otherwise the coolant will start eating the bearings, per Blackstone.
 
I'm already on 60degreeV6.com, as well as MyMonte.com, w-body.com, clubGP.com, and L67swap.org.

I just don't think that repairing the 3100 is the best option. It's been exposed to coolant/water for long enough that I don't trust the bearings. The heads are most likely warped so that's something else I'd have to fool with, so just replacing it with a 3400 should be cheaper, and gives me the added bonus of an extra 20 hp (which this car needs).
 
My views on this:

-Swapping out a 3100 for a 3400 is going to harm your resale value for an everday person is buying it.
-Fixing this engine you have is cheap on parts, and a slight pain in labor for you.
-Replacing the engine is more money and a BIG pain for you in labor.
-If your true intentions are to sell it, why not just fix this engine and get rid of it?

Anyways if you have not done so, switch to green coolant now at a 70% water 30% coolant mix, and use a cheap oil every 1.5-2k miles for the time being.
 
Warped heads can be milled. We do several of these a year and always have the heads milled. Almost all of them are a little warped.

Swapping a used motor, whether a 3100 or a 3400 will be a gamble as the gaskets on those could go at any time.

Fix the gaskets and sell the car.
 
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