Hi Everyone,

I have a 2001 Monte Carlo SS with a N/A 3800 that's sitting at around 240k miles right now. Everything still runs pretty well and while I don't drive it every day anymore, I still use the car pretty regularly. 5 years ago when the car was at 160k miles, I replaced the upper and lower intake manifolds and gaskets (originally was just going to do the gaskets, but the lower manifold cracked during disassembly so I just did everything). I used all Dorman parts including their redesigned upper manifold. Today, I was topping off the oil in the car like I usually do every few months (it consumes/leaks maybe 2/3 of a liter every 3k miles) and I noticed that the inside of the oil fill cap was pretty frothy looking. I also noticed that the coolant reservoir was below the fill cold line even though in the past the car hadn't been losing coolant. I shook out the oil cap and got some watery liquid that was almost definitely coolant, the exhaust has also been a little "steamy" lately even when the engine is warm, which might be a side-effect of a northeast winter, but could also be coolant consumption. I'm pretty sure at this point the car is burning at least a little bit of coolant, and I want to fix this before it becomes a real problem (or gets too cold to do it).

Does anyone have experience with the expected lifespan of the Dorman intake manifolds / gaskets? I've put 80k miles on them since installing so I'm wondering if maybe its just time for a new set of gaskets. It's honestly not a lot of work to change them so I probably will, but I'm also wondering if maybe its also worth the effort to change the head gaskets. I know they don't normally fail, but 240k miles is a lot. Sometimes I let the car sit for close to a week without driving it, so that might be accelerating the wear on things a little bit. Any ideas or insight is greatly appreciated!

 

No experience with Dorman manifolds. The mileage you have since you did the gaskets is good chunk of miles. Did you use the standard replacement plastic gaskets? If so, they are most likely failing again. If you did the metal core gaskets, they might be alright.

Your best move is get a radiator pressure tester from the auto parts store loan-a-tool, pressurize the system, then look and listen for a leak. Since your description basically confirms coolant in the oil, my guess is a failed upper or lower intake gasket and/or a failed upper intake. The upper intakes can develop a hole where the EGR stove pipe comes up, which is between two coolant passages. If a hole develops, coolant can spray into the upper intake (if it does, you might also get white smoke out of the exhaust).

Pressure testing can help you quite a bit.

 

I'm having a hard time remembering exactly what the replacement gaskets I installed were made of. I can't find the details from when I originally ordered the parts, but it looks like Dorman only sells plastic lower gaskets now, so that's probably what I currently have in the upper and lower. I know I bought the updated design upper manifold, so I don't think that will be a problem but when I open everything up I guess I'll find out.

Does anyone know what the generally recommended upper/lower gasket manufacturer and part number are? I see ACDELCO has a metal lower gasket design that's supposedly for supercharged applications, but I can't seem to find one for the L36. Fel-Pro has a metal gasket (model MS98014T) that looks like its designed for the L36. I'm probably going to order them and try to get it done soon.

 

The upper intake gasket is all plastic (but it's usually less likely to fail, but I would replace it any time you are exposing it).
I am 99% sure the lower intake gaskets are the same for L36 and L67.
Here is the listing Rock has for the FelPro metal ones:
https://www.rockauto.com/en/moreinfo...68402&jsn=1031

 

So a little bit of an update, its been busy lately but I've just had some time to work on this so I tore everything down and replaced both gaskets. When doing the uppers, I noticed that there was a redish film (pretty sure it wasn't oil) under the upper manifold, which might indicate that coolant was entering via the upper manifold in very small quantities, kinda like what I was seeing. I also noticed that the upper manifold bolts were really loose (some of them felt hand tight) which could be a problem caused by me when I replaced everything the first time. I think I didn't fully torque the bolts because I was afraid of cracking the lower manifold (which happened the very first time I attempted the repair). This time I torqued everything to spec, and in a week or so I'm going to go back in and re-torque everything because the gasket could compress. I used an ACDELCO 89017554 replacement upper manifold gasket.

Here's the engine with the upper manifold off, you can see the red film under where the manifold was meeting the engine. I'm not entirely sure where or if the coolant could have been entering the manifold, but it certainly shouldn't be anymore. I have a redesigned upper manifold on there and I couldn't see any signs of a hole forming near the EGR pipe. The engine looks a little gross in this picture but I used this process as an opportunity to clean things up as much as I could.



Upper intake removed

It turns out that the first time I did this repair, I used the Fel-Pro metal gaskets for the lower, but it's a good thing I opened it up anyway because it looks like the manifold end seals were starting to leak oil down both sides of the block. It didn't look like metal gaskets themselves were starting to fail, but I replaced everything anyway with an identical Fel-Pro set (MS98014T). Here's the block with the lower manifold removed and the old gaskets still in place:



Lower manifold removed

After swapping the gaskets, I changed the oil and ran the car for a while checking for anything out of the ordinary. I haven't driven it enough yet to definitively say it's fixed, but now I don't see any steam/smoke out of the tailpipes once the engine warms up, which seems like a good sign. I'm going to keep an eye on things, and if I'm still losing coolant I'll do a pressure test to try and track down where. One other thing I noticed is that when I drained the coolant, it was crystal clear with no sign of oily film. I wasn't originally planning on reusing it, but it looked brand new to me. This suggests that oil isn't getting into the coolant, which makes me feel a little better about things.


Crystal clear coolant!

I'm going to keep an eye on things and let you know if there are any updates or new discoveries. Thanks for the help!