unknown coolant leak GM 3100 V6`

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Hello. I noticed one, single drop of coolant on the ground when I changed my oil yesterday. I had originally assumed the water pump was starting to weep, but alas it's holding strong. Doing a little looking around, I found some puddled coolant on the drivers side, originating near/under the throttle, and dripping down from there. It's not landing anywhere hot enough to boil it off, and I'm not really sure what gaskets are in that area to begin the process of stopping the leak. Picture 1 is a sensor directly below the throttle body, a few inches in from where the upper radiator hose meets the engine block. Picture 2 is simply a lower puddle from above, just including as a just in case. I've already cleaned the area with some dawn power scrubber in hopes of better pinpointing the leak. Anyway, those of you with knowledge of the 3100 V6, or with more knowledge than I, any ideas?
 

RichardS

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RockAuto has a list of options, with Mahle being the only set to include all the miscellaneous gaskets And seals, along with the manifold bolts. it's not the fel-pro that are usually suggested, but Mahle is still a good gasket, yes? edwardh1, by the time they built mine, they'd been building it for 23 years. The GenII in my car originated in 1984. Was there a big change in the later years that you're referring to? Other than the well known manifold gaskets (making itself known here), I'm not familiar with any major issues.
 

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As a sidenote: 901memphis, would it be any easier to change the rear plugs with all of the parts off to replace those gaskets? If I'm going to have it apart anyway, it would be a perfect time to replace those.
 
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Run your hand under the heater by-pass hose/pipe in that area just to rule out that out before blaming the intake gasket. If the lower intake manifold gasket is leaking its not the end of the world. There is an improved design Fel-Pro gasket set available. This is a labor intensive repair for an advanced DYI'er, or around $800 or so by a competent mechanic, preferably one who has done the job before. Once repaired the 3.1 engine can easily go 200,000+ miles.
 
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Originally Posted By: RichardS
it's not the fel-pro that are usually suggested, but Mahle is still a good gasket, yes?
No, get the Fel-Pro gasket set, this is not a job you want to do twice. Yes, good time to change out the rear plugs. FYI- I've reused the intake bolts, cleaned with a generous amount of Loc-tite and carefully re-torqued in sequence.
 
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There's two fel pro sets make sure you get the metal ones! Good time to do the plugs, get iridium since the waste spark system is hard on plugs. I agree with taking a closer look just to double check the source of the leak, but the LIM gaskets are way too common of a failure point
 

Nick1994

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When the words GM 3100 and coolant loss are used in the same sentence, it's automatically a no brainer what the problem is. Lower intake manifold gaskets.
 

RichardS

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Where the coolant is at, from what I can see online, it's either the LIM, or the housing for the thermostat is cracked. That would also explain the goop O found when I flushed it. Must not have been old Dexcool goop, and instead was likely oil. I haven't found any in the new coolant, but it was down a little in the overflow, and I'm sure there will be oil when I take off the radiator cap. I did see the iridium was oem, and with the $3 a plug mail-in-rebate, they're only $2.45 a plug. Eh, I still went with the Mahle/Victor Reinz. There wasn't a fel-pro kit that included all the seals and new bolts. If I have to do it again in a few years, I'll let you know so you can tell me you warned me. The Mahle is metal with rubber seals, identical to the fel-pro. It's also being cleared out, so it was a painful $46 for the kit. I can live with that. Looks sturdy enough to me, no?
 
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Originally Posted By: edwardh1
GM did a huge disservice to people when they built that engine. why did they change from what they were using before.???? without testing
There were several engines which had intake gasket issues. Once done with improved gaskets, those engines will go a long time.
 
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Originally Posted By: 901Memphis
There's two fel pro sets make sure you get the metal ones! Good time to do the plugs, get iridium since the waste spark system is hard on plugs. I agree with taking a closer look just to double check the source of the leak, but the LIM gaskets are way too common of a failure point
+1 Given the picture I would lean LIM because it is a common problem on those engines. Without really getting in there myself the armchair mechanic in me says LIM. Also, I would def. change the plugs with Delco Iridium. Those engines can be a pain to change with all the stuff on top of it. Might as well do it while you have the room
 

e40

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Originally Posted By: Bgallagher
+1 Given the picture I would lean LIM because it is a common problem on those engines.
Same here. Helped a friend do his almost 4 years ago, it took us about 8 hours including a trip back to Autozone to exchange the gasket. (The wrong gasket was in the box). It's still holding up good.
 

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Originally Posted By: Trav
The second picture is troubling me, is that outside the engine just below the head and no where near the LIM?
Trav - that is directly below the upper puddle, but at the very bottom of the engine. Away from any hoses or gaskets, down by the starter I believe. After a cleaning yesterday, and a drive to/from work, both have returned. The upper leak is literally where the LIM gasket sits between the manifold and engine. I'm going to clean both areas again, and let the car idle to see where they're coming from.
 
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Most likely the LIM but warped heads are not unknown on these if it got hot. Just make sure before you go doing the job and find out later it was all for naught. The ACDelco is a great plug made by NGK, it is essentially the same plug, copper core, iridium tip with nickel ground electrode and a platinum puck. Be sure to put new wires on at the same time as you will probably either break one or have to cut the boots of the rear bank to remove them, ACDelco OE from Rock are a great buy for this one.
 

RichardS

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Trav, thank you. Beyond just cleaning and watching for the leak, I'll also put a rag at the source of the upper leak to see if the lower puddle returns, or is just drip down from the upper leak. The car hasn't over-heated since I purchased it in January, and this weekend was the first time I've noticed the leak. When I bought it in January, the coolant in there looked like the original Dexcool; beaten, battered, and driven through [censored] and back. It didn't show any signs of having newer coolant added to it, or look too off color or diluted by the addition of water. if the ACDelco and NGK are the same plug, then the price point on the ACDelco after MIR wins the race! I'll add in a set of wires, I had initially just figured I'd reuse them but it's better safe than sorry. Are you aware of the difference from the ACDelco and ACDelco professional? The professional are under the 'premium' tab, and just about half the cost of the standard replacement ACDelco wires.
 
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Originally Posted By: RichardS
901Memphis, any reason you prefer the NGK5599 over the Delco Iridiums? $2.45 a plug is hard to pass up for iridium plugs
Whichever is cheaper they are the same part from what I've seen. I ended up getting the Delphi XS10390 for about $29 they seem really similar to the OE wires for a little cheaper.
 
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