Name that drip

Hey y’all - '99 Yukon, 5.7L Vortec, 113k miles. Drip under the engine bay, slightly oily to the touch, faint green in color. Where I see the drip hanging is where the front driveshaft meets the diff, and on the part just underneath it. Not saying that's where the source of the drip is, just where I see it hanging when I get down on a knee and look from the side of the truck (haven't gotten completely underneath it yet).

Coolant, right? Any guesses as to the most likely culprit, things I should look for as far as telltale signs so I can go to the repair shop a little more informed?

Many thanks!

Sounds like coolant to me. Check the water pump and the area where the water pump meets the block or the weep hole for the pump. If it is coming from the pump or the weep hole get a new one. I just picked one up for a '95 for 20 bucks at the local Flaps.

you are supposed to have colored Dex-cool for coolant. not green propylene glycol. inform the shop to flush out the wrong stuff.

Thanks guys. Sunlit, are you saying that having the wrong coolant in there could be the entire problem (because for instance it has certain characteristics that allow it to leak, whereas the right stuff won't)? Or, that there is likely a standalone problem (such as a bad gasket) and that in the course of resolving that issue I should also make sure that the right coolant gets put in?

PS when you say it should be colored Dex Cool, is there a particular color that is appropriate for my engine?

forget the ability to leak theory. green coolant silicates can help inhibit corrosion of the aluminum of the manifold. but that and other additives in green coolant wear out chemically more quickly. hence you have to change it often. it can also allow damage to other parts quicker before you would notice it. your leak is more likely a seal or gasket thing. it also can be part effected by the wrong fluid but those odds are lower statistically speaking. there should be no green fluid on the vehicle at all so either you just happen to have a typical leak to repair and possibly a fluid change is needed or something is very wrong with a correctly used fluid used in the vehicle. check your rad if it has green coolant then it may be obvious that you have a coolant leak somewhere. if that is the case flush out the entire system with the heater temp set to warm or higher, fan can not be in the off position but speed does not matter, water must come out clear. then disconnect the lower hose. pour distilled water down the thermostat housing opening with distilled water to flush out the regular water. put the lower hose back on and fill the engine with a 70% dex-cool/ 30% distilled water solution thru the thermostat opening and squeeze the lower hose to bleed out air. when filled to just below the housing mating surface install a new 195° stat with gasket. then hose. fil radiator while squeezing the upper hose. top of rad and fill reservoir to full hot. after a few heat cycles the coolant level in reservoir should be checked and refilled based hot or cold engine. do not ever mix green with orange coolant it can lead to serious damage. track you leak carefully. if you have too you could always uv dye it. dex-cool is orange.

Many thanks for your detailed response! Very helpful, most appreciated.

anything else just ask.

Update, as a token of my appreciation for this forum's willingness to help...

The green in the coolant, I'm told, is just dye - not that I know why it's dyed (I didn't ask), but I was assured the correct (Dex-Cool) coolant is in there. Anyone who has any knowledge on this and wants to provide it here, by all means please do....

Took 30 mins of pressure testing before the leak revealed itself but it was indeed at the water pump, so that was replaced. Parts (genuine) and labor, ~$600.

This truck did a lot of sitting in the garage for the last few years before I bought it from the old man, so these things are starting to make themselves known. But that's one more thing now off the list! A proper tune-up and a new A/C compressor and I do believe I'll have a basically brand new truck.

Thanks again!

$600 to change a water pump!?!?
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