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Bypass coolant tube seeping

04-16-2012, 08:46 AM
I am chasing a small coolant leak on my 2003. I suspect it's the bypass tube seeping around the o-ring at the lower intake manifold. I cannot actually find liquid coolant lying on the metal underneath.

Does this coolant evaporate when it seeps out of the seal? I expect it to only leak when the engine is hot enough to be under full pressure. I found a teaspoon of coolant under the car on a plastic piece I had put down after driving it 90 miles back from Columbus a few weeks back.

I have put fluorescent & UV dye into the coolant and don't find a lot of the color on the metal under the bypass tube, but there did seem to be some--dry? When I used water to flush that area, the dye seemed to show back up.

I had suspected the water pump at 130,000 miles. But the inside of the pulley shows no signs of dye, dry or not. The pump has a slight wobble to the pulley and very slight bearing feel, so I have a replacement here ready to go. But it's not my leak source.

How can I verify my leak problem. (It's not internal: an oil analysis showed no coolant in the oil.)

Tech II
04-16-2012, 09:31 AM
The plastic elbow must have a slight crack, and is slowly leaking....when they completely break, it pours out.....usually a pressure tester will show the replace, you have to remove the whole tensioner assembly.....there is a second elbow down below....not the same size...should be replaced at the same time.....clean out the bores of all crud and lube the orings with petroleum jelly for easy reassembly......use OEM elbows/orings....there have been some problems with aftermarket brands....

04-16-2012, 09:57 AM
As a preventative & precautionary measure @ 130K, I would replace the pump and bypass elbow. The pump has a weep hole in the drive shaft neck, that allows coolant to seep out when the seal fails. This particular drip/seep will not necessarily show up behind the drive pulley, it just leaks down the front of block, or evaporates. Contrary to popular belief, (unless cracked) the bypass elbow/o-ring will NOT normally leak @ operating temp, but as the engine cools down and goes from pressure to vacuum. During normal driving, heat & pressure tend to provide expansion of the elbow & o-ring, thus preventing leaks. In addition, the elbow/o-ring leaks seem to be more prevalent with the engine cool & ambient temps below 50 deg.

04-16-2012, 10:21 AM
The plastic elbow must have a slight crack, and is slowly leaking.

The bypass elbow was replaced in July 2010 when a local independent changed my upper and lower gaskets for me. I didn't trust doing it myself with a trip planned the next week.

I did use a pressure tester on it last summer/fall to see if I could determine a slow, occasional seep. ON the hot engine I got nothing other than a drop in pressure due to cooling of the water within the engine. Leaving pressure on it cooled down, overnight at least 9 hours, I got a drop to 12# (from cooling?) by morning and a 10-12 drops of green coolant under the bypass elbow at the LIM. This supports the idea that the o-ring leaks when everything has cooled with their individual expansion indices.

I'll check from underneath the water pump to see if I get any UV fluorescing from coolant through the weep hole and down the block. The water pump is getting replaced for sure. But it doesn't require removing the alternator and idler unit.

04-16-2012, 06:59 PM
As a side note get an oe elbow from a GM source I have had no luck with a/m parts.

04-19-2012, 08:59 AM
Replaced water pump. On 2003 leSabre, it's easy. The access to 8 bolts if good. The difficult part of scraping the old gasket off the engine facing. It would look smooth but there would be a layer of old gasket in places. I would scrape vertically with the razor blade or putty knife and the surface would roughen again with the paper layer. Soaked with antifreeze which made it easier to peel and got it all off.

I see why people have trouble with leaks when the replace the pump and didn't get all the old gasket off because of the way it looks after removing layers with the blade.

Question: While the pump was off I looked at the bypass tube in the UIM. It's way back. How hard is it to remove the old (fairly new) tube and clean the sealer the mechanic put around. It's back in deep.

What sealer do I use to replace the o-rings and new tube for lube and sealing?

I'm tempted to take it back to the original mechanic now that I know it didn't seal perfectly from two years ago.

Tech II
04-19-2012, 04:24 PM
As I said before, no sealer is necessary......problem is, some of the aftermarket parts used, do not seal well....the bores just have to be thoroughly cleaned, and like I said, apply petroleum jelly to the O-rings, and it will seal can't remove the tube without removing the whole tensioner assembly.....and when you do that there is another elbow(different size) located in the lower part of the assembly that has to be replaced too......this is a fairly simple job......just line those elbows up straight, and install the tensioner evenly, and there should be no problem.....anyone who puts sealer on these elbows doesn't know what they are doing....

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