Yes, the TB has to be removed in order to replace the plenum.

Here is a decent pictorial on how to remove the upper and lower plenums.

https://www.gmforum.com/mechanical-1...ts-l36-297702/

On another note, if your doing the LIM gaskets, get an oil change kit. Filter and 5 qt jug of oil so you can change the oil AFTER the intake job is done. You will get coolant down into the oil valley then into the oil pan. I suggest draining the oil first, LEAVE the drain plug OUT until everything is done. Then put plug back in and refill with oil and then change filter.

This car was in the family and I acquired it recently. I was told that it was leaking coolant but it was a slow leak and they could not find the source. I was told that it was so slight over a long period of time that they just added coolant. I drove the car Friday and it was a cold day; the exhaust was normal so I don't think it is burning any coolant that I could see; no clouds of steam.

I am going to drive the car today and then check how much coolant I find in the intake duct; the amount if the photo could have collected over a long period.

The LIM gasket does need to be replaced; so maybe I can get the shed vacated and just do what is needed; too bad they did not have the foresight to go ahead and replace the LIM gasket when the new UIM was installed.

Thanks so much for the pictorial; that is really going to help.

If coolant is leaking inside of there I'd highly suggest not driving it, if a little coolant gets sucked into your cylinders it will not compress, so it has a chance to break a connecting rod, possibly throw it through the block, and/or damage the pistons. If that happens you are going to be rebuilding the engine, or getting another one, which equates to a lot more money, and work.

I picked up the throttle body gasket today. My plan is to replace the throttle body gasket and see if the coolant leak into the intake duct stops and to keep a check on the coolant level. It is possible they may have reused the old throttle body gasket when the UIM was replaced. If it appears there is no coolant lost, then I can wait on doing the tear down to replace the LIM gasket after I have put the tractor back together and have the shed to use for the job.

What are the thoughts on this plan of action?

With how little coolant it takes to ruin a cylinder, it is hard to call.
If you open it up and find the throttle body gasket is definitively the problem with the coolant getting in the throttle body, then you may be ok for a while, but I'd not put it off for too long, those plastic LIM Gaskets always fail, at 133k miles mine fell apart when I took them off, it was bad, I have heard of some failing as early as 60k or so.

mine was 60 the first time but they didnt have the dorman stuff back then so the second time was about 160-170k. 3800s are tough, the only way you can wreck one is to let go a coolant leak. we see it here all the time and warn against it but people just let it go, sometimes it works out, most times you are in for a new engine. It seems very unlikely a TB gasket, the dorman UIM (any kit i have seen) kits come with new gaskets. having seen several and doing several UIM/LIM/aluminum elbow upgrades, my advise is still the same do it all at once, and dont drive it till you do. you can also get the haynes type manuals on autozone, if you sign up the have procedures and torque specs at least. make sure you use thread sealant on the LIM bolts. and the plastic elbow usually comes out in 50 pieces, make sure you have a hook or something and pick all the pieces out, and i put a little ultra black silicone on it for insurance

and a few of us block the coolant from being in the upper intake at all, heat is the issue, from the coolant and egr. the new dorman kit comes with improved egr and blocking the coolant is extra protection.
its not necessary but for as little work as it was seems justified to me
https://www.gmforum.com/mechanical-1...2005-a-304071/

Plastic gaskets? What idiot came up with that idea?. OK guys, you have me convinced; I am taking the UIM and LIM off the car and getting what is needed to fix this job properly. It should have been done the first time by the previous owners; they decided to cut corners. I am surprised they did not ruin this engine as it was loaned out to two family members to drive when their vehicles were down and all the time it had this coolant leak.

I will put the tractor back together enough to pull it out of the shed; I can cover it with a tarp, and the 98 Buick is going in to be fixed properly.

Thanks for the help everyone; this board is a valuable tool for GM owners.

What is the purpose of the coolant in the upper intake/throttle body; to warm the air before it enters the combustion chamber?

the only thing anybody has been able to come up with is that it warms the TB for cold weather, but i live near buffalo, and the guy i got it from was from new england, i think it would have showed up by now, it gets into the negatives for highs here and my wife drives the car like 80miles a day. i did it a few years ago and have not had any issues so far.