Write-Up: Lower Intake Manifold (LIM) Gaskets

Well, we were able to figure out the LIM gasket ordeal. It made sense the more we looked at it. Like dummies, we bolted down and torqued the LIM bolts without putting the coolant elbow in place. I forgot to clean both openings too. My uncle took a piece of string and tied it around a screw. He fished the screw through the coolant openings and pulled outwards and all of the broken coolant elbow came out in one piece.

Everything else has pretty much been going smoothly. We just need to add coolant, bleed the system, put both belts on, put the intake tube on, and we should be good. Oh wait, forgot about the stupid vacuum hose. When I say we "ghetto rigged" some things, I mean it. As long as they're air tight, I don't care how they look.

I'll also change the oil in auto shop because I can use a lift in there. Makes things a little easier to do.

I thought I'd put the LIM repair to bed last June but find I'm still burning coolant.

My Blackstone Oil Analysis shows a decrease in Antifreeze contamination from about 0.42 % to 0.24% in the crankcase oil since the repair but the level in the overflow tank slowly goes down.  I'm burning a few ounces a day it seems.  

Was I supposed to use RTV or some other sealant on the LIM gaskets or the "O" rings that seal off the  Throttle Body coolant passage?  I wouldn't think so.

I torqued and re-torqued the LIM and Supercharger bolts to specification, in accordance with the FSM sequence after getting all surfaces scrupulously clean.

Does anyone have an idea why this LIM gasket replacement would continue to leak?

A friend suggests that the head gaskets could be leaking but this doesn't seem likely and I've not heard of that being a problem on these engines.

Can you smell coolant ever? The reason I ask is that a very small hole in the Radiator would make the Coolant level drop slowly. You'd smell it once the Cooling Fans kicked on. My Radiator has been doing this for about 4 years. It's not touching the ground, so I haven't bothered.

No, I don't smell coolant, but I do see suspicious puffs of whitish exhaust when the engine hasn't warmed up.

I've been chasing coolant usage for at least a couple of years and replaced the cracked radiator with the radiator hoses, coolant elbow with an aluminum one a couple years ago. The water pump right after I got the car with 98k on it. Those repairs didn't eliminate the coolant usage so then I did the LIM gasket replacement last summer.

I can't continue to ignore the fact that the coolant level consistently goes down so at the last oil change I sent an oil sample to Blackstone for confirmation.

Even if I'm losing a bit of coolant outside the engine, I've still confirmed there's coolant in the oil.

Has anyone found deteriorated head gaskets when they've had the heads off?

I am wondering if you have some porosity in the casting of your particular engine block.

Is there a way to test for that?

Does anyone have any other tests to suggest? I'm afraid I'm losing my grip on reality at this point

That, or I'm overlooking the obvious.

What you **can** do is put stop-leak tablets in the coolant. An old-school gearhead at any GM dealership will confirm that in the era of the Riv, standard procedure for changing coolant in a 3800 was to put stop leak tabs in the radiator. Basically the stuff is ground up walnut shells, ginger root and or some such, but it does work. If you look in the factory manual for the Riviera, you WILL ( I repeat WILL ) find that it says to drop those seal tabs in when you change coolant. In the past GM has issued warnings about NOT using the tabs. If you do a web search (google) "gm 3800 engine coolant leak stop leak tabs" you will find several posts about this, and a GM TechLink note from March 2004 on the topic.

I think that's (stop-leak tablets) the obvious solution that I've been overlooking.

With the FSM blessing I can stop obsessing over a minor problem and move on to fry bigger fish.

Thanks albertj

albertj wrote:

What you **can** do is put stop-leak tablets in the coolant.  An old-school gearhead at any GM dealership will confirm that in the era of the Riv, standard procedure for changing coolant in a 3800 was to put stop leak tabs in the radiator.  Basically the stuff is ground up walnut shells, ginger root and  or some such, but it does work.  If you look in the factory manual for the Riviera, you WILL ( I repeat WILL ) find that it says to drop those seal tabs in when you change coolant. In the past GM has issued warnings about NOT using the tabs.  If you do a web search (google) "gm 3800 engine coolant leak stop leak tabs" you will find several posts about this, and a GM TechLink note from March 2004 on the topic.

Why would it require stop leak tablets?  Were the tolerances to loose, a defect, or something else?

98riv wrote:

albertj wrote:

What you **can** do is put stop-leak tablets in the coolant.  An old-school gearhead at any GM dealership will confirm that in the era of the Riv, standard procedure for changing coolant in a 3800 was to put stop leak tabs in the radiator.  Basically the stuff is ground up walnut shells, ginger root and  or some such, but it does work.  If you look in the factory manual for the Riviera, you WILL ( I repeat WILL ) find that it says to drop those seal tabs in when you change coolant. In the past GM has issued warnings about NOT using the tabs.  If you do a web search (google) "gm 3800 engine coolant leak stop leak tabs" you will find several posts about this, and a GM TechLink note from March 2004 on the topic.

Why would it require stop leak tablets?  Were the tolerances to loose, a defect, or something else?

Why? I'll give you 3 guesses and the first does not count

1) elves that get drunk off pink poly-glycol have to get their binge from somewhere - why not your radiator expansion tank?
2) expansion-cooling mismatches between the cast iron block and aluminum head/accessories permit seepage over time
3) minor porosity in the water-cooled castings
4) because the plastic engine gaskets leak little sprays of coolant under heat and pressure
5) because the trade-off between quality and reliability versus marginal costs gets made by folks who have developed some skill in having others take the fall when they get it wrong
6) stop-leak-seal-tabs are cheaper than the metal they substitute for and last for the relevant warranty period

Which of the alternative answers above do you like best?

GM puts those tabs, or a form of, in every single car when it rolls off the assembly line.....it's probably not even a GM thing. They probably all do it.

Why tear engines apart to find a pin-hole when you can just seal it up with magic beans?

OK, I have started the LIM gasket and Valve cover gasket repair on my 98 RIV. I have the UIM and LIM both removed. Broke one Packard connector to MAP sensor and two vacuum fittings/lines that are in the MAP circuit as well. I was fairly gentle, but my machine is 22yrs old and everything is brittle....everything looks original too. Question, have any of you sourced a vacuum fitting/hose kit specific for this vehicle? Have any of you sourced a kit that may not be specific to the 98 RIV but had enough generic stuff that you could piece the system back together.

See attached photos for job in progress:

https://photos.app.goo.gl/ibm9QWMHXfc7suZg9

Last three photos will show some of the vacuum fittings/hoses in the MAP circuit i'm referring to. Any help and or feedback would be appreciated.

98RivOwner wrote:

OK, I have started the LIM gasket and Valve cover gasket repair on my 98 RIV. I have the UIM and LIM both removed. Broke one Packard connector to MAP sensor and two vacuum fittings/lines that are in the MAP circuit as well. I was fairly gentle, but my machine is 22yrs old and everything is brittle....everything looks original too. Question, have any of you sourced a vacuum fitting/hose kit specific for this vehicle? Have any of you sourced a kit that may not be specific to the 98 RIV but had enough generic stuff that you could piece the system back together.

See attached photos for job in progress:

https://photos.app.goo.gl/ibm9QWMHXfc7suZg9

Last three photos will show some of the vacuum fittings/hoses in the MAP circuit i'm referring to. Any help and or feedback would be appreciated.

You can still get the vacuum manifold from any GM dealer if the parts tech will bother to look it up,, knowing that it's the same as the one used on the late model SC 3800s. Or just order the kit from ZZP, it's 2 brass tees and a sufficient length of hose for $20 ++, OR a genuine GM replacement from Intense for about a buck less. All that really happens is the rubber fittings get hard and brittle, for some reason they designed in hard hose and soft fittings. The manifold replaces the entire vac line set from MAP to SC Bypass, including even the tee to the fuel pressure regulator.

Thank you Albertj, I ordered the OEM kit from Intense.
I thought you would comment on the poor condition of my TB, gonna clean it really good while it's off. It's in terrible shape.

brutusk1 wrote:

I think that's (stop-leak tablets) the obvious solution that I've been overlooking.

With the FSM blessing I can stop obsessing over a minor problem (small coolant leak) and move on to fry bigger fish.

Thanks albertj

Update: It turns out that the radiator - a brand-new A/C Delco radiator had been leaking since I first installed it.  When that radiator sprung a larger, structural, leak in a couple years, I replaced it with a Chinese-made radiator and it's been leak free ever since.  It was quite a disappointment that the A/C Delco radiator leaked from when it was new, and totally failed after about 35k miles.  

I love opening the hood and seeing that the coolant level hasn't gone down at all in since mid-year 2019.

brutusk1 wrote:

brutusk1 wrote:

I think that's (stop-leak tablets) the obvious solution that I've been overlooking.

With the FSM blessing I can stop obsessing over a minor problem (small coolant leak) and move on to fry bigger fish.

Thanks albertj

Update: It turns out that the radiator - a brand-new A/C Delco radiator had been leaking since I first installed it.  When that radiator sprung a larger, structural, leak in a couple years, I replaced it with a Chinese-made radiator and it's been leak free ever since.  It was quite a disappointment that the A/C Delco radiator leaked from when it was new, and totally failed after about 35k miles.  

I love opening the hood and seeing that the coolant level hasn't gone down at all in since mid-year 2019.

Thanks for the update!

98RivOwner wrote:

Thank you Albertj, I ordered the OEM kit from Intense.
I thought you would comment on the poor condition of my TB, gonna clean it really good while it's off. It's in terrible shape.

I don't recall info about your TB.

No info explicitly, just a photo of the TB throat in the link I gave in the OP. Its in horrible shape.

98RivOwner wrote:

No info explicitly, just a photo of the TB throat in the link I gave in the OP. Its in horrible shape.

I took a second look.  It's not that bad but will work better after cleaning.  Be sure to get the IAC air passages clean and be very, very careful not to damage or alter the air screen.  You will need to remove the IAC solenoid and the MAF. You may need a 'tamperproof' Torx bit. Brass orifice brushes may help as well.

Once upon a time a mechanic I know at my local GM dealer (who now is a service writer in dealer's body shop) told me he takes all the accessories off the TB and then soaks the whole assembly in a bucket of TB-safe cleaner.  Not sure I want that much solvent around, and I've been happy with results from the little cans of CRC TB cleaner.

CRC TB cleaner is what I plan to use. Just gonna clean it manually, no soak, but I do see how that might be more effective at getting to hard to reach surfaces. Will heed advice on screen, IAC and MAF.

Thanks.

Cleaned the TB, removed the IAC and MAF sensors, CDC stuff worked well. Gonna clean the UIM next.

BTW, I thought it would be wise to replace the heater hoses while I had the top end off. Man those things are a bugger to access. Got them off today, struggled with them for a couple of hours. My arms are too short and big to work between the engine and the firewall. I had one of these and it helped, but still tough.

https://www.amazon.com/dp/B01JBL7TA2?ref=ppx_pop_mob_ap_share

OK, I finished up this job on Saturday August 29th(been doing it as I had time, company in town etc). I replaced the LIM gaskets, UIM gasket, TB gasket, valve cover gaskets, cleaned the TB, replaced the coolant elbow in LIM, replaced the tensioner for the main belt, replaced both heater hoses and Orings, replaced PCV, replaced MAP sensor GM connector(broke locking tab during dis- assembly), fuel injector Orings, replaced oil in Supercharger, new air filter(found rats nest in bottom of air intake, cleaned that out) new Dexicool and distilled water and had just done the plugs and wire a couple of weeks before.

Been driving it a couple of days, had a SES light come on with a 1635 code( reference voltage to MAP, EGR and/or TPS out of range), turns out when I replaced that MAP broken connector mentioned above I got the A and C pin locations reversed on the repining effort, swapped those back to correct positions and all satisfactory now. No leaks that I can find. Runs better too.

Hose picks are a real life saver on this job - link

I cut the heater hoses Jack with a razor blade knife since I was replacing them. The upper radiator hose I removed from the thermostat housing cover after I had removed the cover from the LIM so the hose came off easy and I reused that particular hose.