3300 - watch for the plastic nipple failure at intake manifold

[Cressida]

I had a very small coolant leak that was showing up at the top front of the engine around the intake manifold gasket area (on the 3300 engine). It seemed to be worse in cold temps. It looked like coolant was seeping out from the manifold gasket. It turned out that the plastic nipple for the short 5/8” coolant hose that goes from the water pump inlet pipe into the intake manifold had cracked. When I was checking around and checked that hose connection, the nipple completely separated on me. I had to slowly remove all the old plastic that remained in the manifold threads and then replace the nipple with a metal one from Napa (3/8 x 5/8” NPT ?) for about $6. O'reilly's also carried one that would work that I believe was a Murry brand.

If this nipple would have failed on a road trip it would have left me in an overheating position quickly as the coolant gets dumped. At best, I would have been stranded for some time. I would recommend 3300 3.3L owners to watch that area for any signs of coolant leakage. I suspect all of them are pretty brittle by now from 20+ years of heating cycles. I started to say you may want to go ahead and replace it at your convenience, but it's probably going to snap off if you try and back it out which may mean a time consuming task of using a small pick to get all of the plastic out of the intake threads. So maybe it's best to just leave it alone? Your call; but be alert and keep an eye on it if you see any signs of coolant in the area.

[93CieraDude]

It's deja vu all over again! (I know its football season, but I have to credit Yogi Berra for that line.) Hey Cressida, I just resealed my intake manifold due to leaks, including a coolant leak at that very same plastic fitting you give a heads-up on in your post.

I keep an eye on a line I previously marked on the coolant recovery tank and noticed that the coolant level was gradually dropping. I periodically had to top-off the coolant to bring the coolant level back up to the line on the tank. Upon closer inspection, I found that the coolant bypass hose was leaking at the plastic fitting you mentioned and one of the heater hoses was leaking at its connection with the heater core. Not only that, the intake manifold was also leaking coolant in two places, as well as a small amount of oil in one corner. With winter coming, I wanted to nip all the small leaks in the bud before they became big leaks. During the intake manifold re-seal, the OEM plastic fitting looked ok, so I opted to leave it alone, but you make a great point about keeping an eye on it. Maybe I'll go to NAPA and buy the metal one to keep as a spare just in case.

From my upcoming album on my intake manifold re-seal, here are some pics showing good views of that plastic fitting and surrounding area during the repair work I recently did. Hope the pics help someone else confronting same issues.

My easy-to-see magic-marker reference mark on the coolant recovery tank.


Bypass hose leaking coolant at the plastic fitting threaded into the bottom of the intake manifold.


Coolant leak on passenger side of 3300 engine - under the alternator, above the water pump/timing chain cover.


Close-up of "four corners" coolant leak; found oil seeping out in same area.


Another coolant leak on top of the drivers side of the engine, under the thermostat outlet below the throttle body.


Close-up:


With the alternator, coil packs and ignition control module removed, the short coolant bypass hose is visible just to the left of the much larger coolant hose connecting to the outlet at the bottom of the radiator.


Close-up: plastic fitting is located at top of bypass hose, just under the larger black wire harness loom.


Removing the bypass hose from the plastic fitting.


Good view of timing cover nipple that the bottom of the bypass hose mounts to.


Needless to say, I cleaned up all that grungy stuff.


View of original OEM plastic coolant fitting on right, 2-pin coolant temperature sensor in center and 1-pin coolant temperature sender on left. Sensor is for fuel management by the engine computer; sender is for the coolant temperature gauge on the dashboard cluster.


Close-up of plastic coolant fitting; seems intact - no cracks. Following the "if it ain't broke don't fix it" school of thought, I decided not to replace it for now. Thanks to Cressida, good to know that a metal equivalent is available at NAPA.


Retained OEM plastic fitting to the right of newly-installed coolant temperature sensor & sender.


Image shows newly-resealed intake manifold and newly-installed PCV grommets and valve cover gaskets & grommets.


New coolant bypass hose.


New coolant bypass hose installed between the plastic fitting threaded into the intake manifold and the coolant passage nipple protruding from the top of the timing chain cover.


With everything disassembled, and given the age & mileage of the car (24 years & 81k+ miles), in addition to cleaning up the intake manifold, I also cleaned the carboned-up idle air control valve & throttle body. I installed new heater core hoses, throttle body coolant hose segment, fuel injectors, valve cover gaskets & grommets, and spark plug wires. Installing new PCV grommets turned out to be a real challenge, though. That's a whole 'nother story, but I eventually finagled a way to get 'em in. The radiator hoses were still in good shape, but I did buy new ones for replacement in the future.

[Skip]

I replaced that plastic coolant bypass nipple long ago. They were known to be a problem back when I was at Buick Service and Parts and the recommendation was to replace it with a metal replacement. Mine is a stainless steel nipple. Don't remember off hand who the supplier was as it was over 20 years ago. But, yeah I would suggest everyone that has one of these still installed seriously consider replacing as they will leave stranded when they crack dumping out all of your coolant and if it doesn't destroy your engine first...........it may not be so easy to find on the road when your far from home.

[93CieraDude]

I didn't have the metal equivalent handy when I did this job because I didn't know one was available. But that sounds like prudent advice, so next time I drain or flush my cooling system I think I'll follow-up and replace the plastic original.

This is the kind of thing that trips up an unsuspecting/uninformed vehicle owner - at great cost, too, if the engine fries on account of a sudden catastrophic coolant leak. What was Government Motors thinking by installing a plastic fitting? Just to save a few pennies? Sheesh ...

Anyway, I hope to buy some time with the retained original plastic fitting 'cause right now I'm gonna have to replace clunking struts and worn sway bar bushings before I take the car in for next inspection. So hopefully by next spring I'll get around to it.

Thanks for your input, Skip !!!

[CorvairGeek]

I replaced that plastic coolant bypass nipple long ago. They were known to be a problem back when I was at Buick Service and Parts and the recommendation was to replace it with a metal replacement. Mine is a stainless steel nipple. Don't remember off hand who the supplier was as it was over 20 years ago. But, yeah I would suggest everyone that has one of these still installed seriously consider replacing as they will leave stranded when they crack dumping out all of your coolant and if it doesn't destroy your engine first...........it may not be so easy to find on the road when your far from home.

You had me wondering about ours now. I looked back through the timing chain pictures and I see a silver nipple! I'll probably change the intake gasket between Christmas and New Years anyway. Had the gaskets ever since we owned the car.

[chris.]

I'm about to tackle a water pump job on my 3300 ... anybody have a part number for that replacement plastic nipple?

[chris.]

I'm about to tackle a water pump job on my 3300 ... anybody have a part number for that replacement plastic nipple?

I went to Kohlweiss Auto Parts and they were able to find it for me. I found them to be way more knowledgeable and helpful than the typical local part store monkey. They had a couple catalogs that had the appropriate part, and they were able to get one in a couple hours for $7 and change (indeed, a metal 3/8 x 5/8” NPT, Gilmore part number AHV 90-402 Fitting, "replaces 84724"). They also sold me a "heater hose coupler remover" designed specifically for GM engines, a Lisle 62200, for under $10.

The Lisle tool was basically an easy-out bit, but with straight threads to cut into the plastic. It mostly worked -- the threads are now clear! -- but the plastic side stuck in the manifold just crumbled away when I tried to back out the bit and some of it may have gone into the engine. I got most of it out with some needlenose pliers and ran my shopvac over it to hopefully extract the rest. I might run a hose through there before I put everything back together, though, in case there are still some pieces floating around inside.

I looked up the nipple 84724 on Rock auto and they do have it, but listed as an "A/C service valve" with no known applications. Now why didn't I think to look there?!? #sarcasm ...Rock is half the price, but I'll gladly pay the extra $3 and save the shipping cost for the service from Kohlweiss.

[Young Guy Old Car]

What’s the thread type for a tap so I can get the plastic out of their easy without damaging the intake threads? Is it a pipe thread by chance? I was replacing my bypass hose and put it on the nipple and clamped it down went to the water pump housing and slid the hose on it and clamped it down went back to see the nipple snapped and the hose dangling over the sensor now I need my car in 5 days and I need help so please give me all the facts you got about this job I need them in 36 hours or I’m stranded for spring break

[Young Guy Old Car]

Oh and is it SAE or Metric Threads?

[CorvairGeek]

I'm pretty sure it is an SAE thread.

[Pontiac6ksteawd]

Off Topic - I still think thats an idiotic PCV design..

[Skip]

Off Topic - I still think thats an idiotic PCV design..

On which engine? The 3300?

[2tone]

I replaced mine with Dorman 56152 on the weekend, fits nicely, available from Rockauto. Recommend getting a 3/8" NPT tap as well, instead of picking out the plastic remnants. That would've saved me a couple of hours.

https://www.dormanproducts.com/p-28438-56152.aspx