Possible symptoms of bad intake gaskets?

[93Bonneville]

1993 Bonneville. 180K miles on her.

In the morning taking off from a cold start the car sputters and jerks like its misfiring real bad. If you floor it and launch for a second it clears up and no more problems. Car runs fine other than driving from a cold start. In addition to that the coolant level is always low when I check it.

So between those two things I am suspecting bad intake gaskets and water is leaking down into the cylinders when it sits and cools down. What do you all think?

[J Wikoff]

It's possible. The cold start jerkiness sounds more like ignition related stuff to me or maybe even a transmission fluid thing, but that is hard to tell over the web.

Is there any milky gunk on the inside of the oil fill cap after it's sat for a few hours? Usually, bad LIM gaskets will let coolant seep down into the lifter valley and into the crank case, and the gunk will be the telltale. The Series I didn't have near as much issue with the LIM gaskets that the Series II did, but they can still eventually fail. At your mileage, it wouldn't be a bad idea to swap them. Though I've personally seen the original gaskets go twice as far and further.

If/when you are replacing the gaskets, I'd replace the plastic water neck for the heater hose on the passenger end of the LIM. There's metal ones at most parts stores.

It's not a terrible job. Having done a few, it would take me 2-3 hours.

[93Bonneville]

No the oil is nice and clean. The cooling system has nasty gunk in it from Dexcool, which I already know to flush out.

The car had a bad TPS and did a similar thing from a cold start as well. I can't remember if it went away after replacement and is now coming back again meaning its time for another TPS. I will also be cleaning the MAF sensor and see if that gives an overall performance improvement. This car is some what of a "dog" when driving.

Its not my car but I am trying to keep it alive. I am also ditching these cheap ass Champion copper plugs in favor of some T55 or whatever they are NGK Platinums.

[J Wikoff]

You had dexcool in your 93? Change your LIM gaskets.

[RJolly87]

To clarify, is the coolant always at the same low level every time you check it, or is it consuming coolant constantly? Is it smoking when it is running funky? Any smells in the exhaust? Have you checked the fuel pressure lately to see if it is where it should be?

Also, Platinum's are not a good idea. They don't do well in a waste spark ignition system usually.

[93Bonneville]

I assume it had Dexcool as it has that typical Dexcool sludge in it. This car has the Series I L27. So whatever that means. I have no idea if this motor is even original to the car...

The coolant level is always low when I check it. I add some, check it again whenever and its low again. Not dramatic, but I fill the rad up and a week or a few weeks later when I decide to check it, the coolant is low enough to where I can stick my finger in the rad and don't feel anything. Surprisingly it does not run hot...No smoke. Haven't checked fuel pressure and probably won't until I have a gauge available to me.

As far as the platinums go, that is what I read on here as a recommendation.

[1oldman]

You have a coolant leak somewhere. My guess it would be the plastic by-pass fitting, if it is original. It is underneath the thermostat and in the LIM. There is a small "L" shaped hose connected to it. The GM replacement is metal. Otherwise, check around the engine.

I've been fortunate when my LIM leaks it has always been between the LIM and heads and you could see the coolant laying between the LIM and heads. Never got into the engine.

It could also be the overflow tank, the overflow tank hose, radiator hoses, and the radiator. - BC

[93Bonneville]

Looks like your on to something. I looked around and I am not sure what I am looking at is what your talking about, as I am pretty sure there is no rubber L hose connected to it or anything plastic under the thermostat, but as you can see there is some red crud and a tinge of green along with general dampness. Also around the throttle body. Looks like this is my issue...

[RJolly87]

Not quite. The bypass fitting that is being described is on the passenger side. It is right under the alternator, it is a hose that comes up, curves around, and goes in to the top of the LIM. The leak you are descrbing is likely coming from the coolant passage that runs from the LIM up through the throttle body.

If that is the case, I have the exact same leak. Plan on pulling off the upper intake manifold off, which you may as well replace the LIM gaskets while you are in there. The only thing between you and the gasket is a series of exposed bolts.

If you do this repair, please take pics, as I am still in the process of sizing this one up.

[93Bonneville]

Yeah I thought that might be backwards as I saw the hose by the alternator.

I will run this by my parents, the owners of the car, and see what they want to do. I would totally be all for taking photos of the process providing my parents don't blow it off and decide not to buy the parts or don't care enough about the car to get it done.

If we do both lower and upper gaskets I was told there is a better upper plastic manifold available for sale I should buy and use? In fact I think I saw a kit on eBay for it all. I guess I will go back and read over the threads about the intake gaskets and see...

[RJolly87]

The 'better' reference was likely in regards to the series 2, used in '95-05 on the series 2. The concerns with these upper manifolds are warping. I also am concerned with dryrot, as my car has been in the south all of its life. Engine bay temperatures can get pretty crazy around here.

I also figure, it has been on there for 20 years, a brand new one should last another 20 years.

Also keep in mind, you may want to plan on replacing parts too, o-rings for the injectors, oil change right after, etc.

I admit, I have been feeding mine coolant for quite some time.

We have the L27, used from 91-95 (exact years vary by application). Most marketed stuff is likely for the series 2. Ebay did have some that I just saw, ballparking shy of $150. If yours comes off without issue, with no signs of warping, I would not be afraid of putting it back in.

[1oldman]

An L27 has no upper gasket between the plenum and the lower intake manifold. The only gaskets are between the lower intake manifold and the heads & block, throttle body, the valve covers, the PCV valve cover, the thermostat bonnet, and the thermostat in the bonnet.

You will go insane if you try and get the gasket between the plenum and the LIM. The only LIM/plenum gasket made was for the super-charged L36. I speak from experience.

There are 3 "O" rings in the LIM and Plenum IIRC for the coolant, PCV valve and I don't recall what the 3rd one was for.

It's more than worth it to replace the injector "O" rings and anything else and everything else that may need replacing in the near future or not too distant future. - BC

[RJolly87]

http://www.autozone.com/autozone/parts/ ... 91417_0_0_

Here is a set. It seems like it would be a rubber bit that goes around to help seal. Also has all of the aforementioned o rings too.

I was expecting to replace this on the trip too. Was I wrong?

[1oldman]

http://www.autozone.com/autozone/parts/ ... 91417_0_0_

Here is a set. It seems like it would be a rubber bit that goes around to help seal. Also has all of the aforementioned o rings too.

I was expecting to replace this on the trip too. Was I wrong?

That looks like a gasket set for an L36 (supercharged) plenum to Lower Intake Manifold. My son used aircraft gasket maker for the Plenum to LIM union. willwren didn't use anything as GM did the same - no gasket. You'll see that when you tear down the Plenum/LIM.

LIM gasket: Fel-Pro MS94918-1 http://www.oreillyauto.com/site/c/detai ... old+gasket
- BC

EDIT: You won't need a new upper intake (Plenum) because it is all metal and does not have an EGR valve. - BC

[00Beast]

FWIW, while I'm not saying your car never had Dex in it (Dex is red/orange), it's OEM fill was normal, green coolant, which can do similar things over time, and if someone mistakenly added Dex at one point, it would sludge up like that. Just to be clear.

[J Wikoff]

http://www.autozone.com/autozone/parts/ ... 91417_0_0_

Here is a set. It seems like it would be a rubber bit that goes around to help seal. Also has all of the aforementioned o rings too.

I was expecting to replace this on the trip too. Was I wrong?

That looks like a gasket set for an L36 (supercharged) plenum to Lower Intake Manifold. My son used aircraft gasket maker for the Plenum to LIM union. willwren didn't use anything as GM did the same - no gasket. You'll see that when you tear down the Plenum/LIM.

LIM gasket: Fel-Pro MS94918-1 http://www.oreillyauto.com/site/c/detai ... old+gasket
- BC

EDIT: You won't need a new upper intake (Plenum) because it is all metal and does not have an EGR valve. - BC

The L36 was the Series II NA engine. And the L27 got an EGR valve and plastic upper intake in late 92, so that's what his 93 will have.

[93Bonneville]

Yes mine has a plastic manifold and an EGR valve.

I thought the same thing when I saw the Dexcool sludge. I can only assume some guy at the Autoparts store told a previous owner to use Dexcool and that is what caused it. They didn't start using Dexcool until later on...

As far as replacing the gaskets go, I am not sure when or if they will get done. After running it by my parents who own the car, they didn't seem to concerned or eager to get it fixed. It looks like once I am done fixing my own crap I will just do it for them for the sake of this car. The leak will only get worse and eventually kill the engine in a serious case...

[1oldman]

http://www.autozone.com/autozone/parts/ ... 91417_0_0_

Here is a set. It seems like it would be a rubber bit that goes around to help seal. Also has all of the aforementioned o rings too.

I was expecting to replace this on the trip too. Was I wrong?

That looks like a gasket set for an L36 (supercharged) plenum to Lower Intake Manifold. My son used aircraft gasket maker for the Plenum to LIM union. willwren didn't use anything as GM did the same - no gasket. You'll see that when you tear down the Plenum/LIM.

LIM gasket: Fel-Pro MS94918-1 http://www.oreillyauto.com/site/c/detai ... old+gasket
- BC

EDIT: You won't need a new upper intake (Plenum) because it is all metal and does not have an EGR valve. - BC

The L36 was the Series II NA engine. And the L27 got an EGR valve and plastic upper intake in late 92, so that's what his 93 will have.

I agree, the L67 is the series I and the L36 is the series II. I was incorrect. I did think the '93 did not have the EGR valve yet though. Since the upper is plastic, the parts I posted are incorrect. - BC

[RJolly87]

I was finding myself tempted to find a metal upper and block off the EGR, but not quite sure on it.

[1oldman]

I was finding myself tempted to find a metal upper and block off the EGR, but not quite sure on it.

There are plenty of really good threads on here on just how to do either IIRC. - BC