99er

I was wondering if you guys know what a common leak locations on these on these Tahoes with the 5.7, and also if there is some kind of diagram out there of the coolant system? I do have the Haynes manual but it does not have a diagram. Now I know how the cooling system works basically. I had changed the radiator about a year ago on this car and it has been running fine since, with no loss of coolant. I kind of wish I changed all the major coolant lines as well when I did this, sigh.

Now I know the Intake Manifold gaskets are an issue with this car, but if that was the only problem then there wouldn't be an external leak correct?

External leak location seems to be be just to the right of the oil pan on the passenger side. I can see the coolant on what I believe to be are these metal transmission cooler lines. Not sure if the leak is from those lines however. I just see drips forming there, for all I know the leak is coming from above that area somewhere and just dripping down. It's a very fast leak and a puddle forms right away when the engine is on. Note that all this happened right after I changed the spark plugs, spark plug wires, distributor cap, and rotor. Coincidental? Possibly.

But some times I think that perhaps through the wrenching process of installing the new cap, plugs, etc. I had to get in between a couple of coolant lines, maybe unintentionally stressed a line where they connect and that could possibly be the leak. I ride with my windows down all the time and before this, for the past year, never smelled coolant, never leaked coolant. I just find it funny that driving the car right after performing this basic tune up, I immediately smell a coolant leak, and drips and a puddle form fast. I did go underneath the vehicle while it's running to try to find the origin of this leak. But it's not just on the oil transmission lines, and I doubt the reservoir is cracked but I might just double check that since it's easy and something I can cancel out right away.

73shark

My only suggestion would be to clean the engine well and see if you can see it better then and get a bright lite to help.

MDTAHOE

The intake leak is a very common problem. Most of the time it is only a external leak.

99er

I am noticing some seepage / wet spot around the coolant temperature sensor. Not sure if it's coolant as I haven't ran the car in a few days. The leak coming from this plug makes perfect sense since it's right above the transmission cooler lines, which is where I spotted the coolant drips. I think this was one of the sensors that I had a hard time removing when I drained my coolant last year. There was one that I could not remove. Not sure if this was the one. The one I did remove however, I'm wondering if there is an o-ring on it. I did not replace the o-ring when installing this so perhaps it went out.

Edit: Well looks like it was exactly what I thought it was. The temperature sensor plug was a little bit loose. I tightened it up, took the t-hoe for a spin, and it's not leaking any more. Glad it wasn't a major issue. I am wondering if it might get loose again over time. It's been a year since I last put it in. I wonder if it will loosen up again over time.

DoubleO7

My 99 leaks at the intake/block joint in the back and runs down to the same spot as yours.
I do not yet have milky oil, although I can taste antifreeze condensed to the inside of the oil filler cap.
I am getting the parts to do the manifold gasket change in a week or two.

99er

Yah, well, it looks like the cause of my leak was something else. It's not leaking from the block, it was leaking from the temperature sensor plug. I had removed that last year to fully drain the coolant. I believe I was suppose to add loctite to the threads when reinstalling it so that it wouldn't loosen over time. So that mistake finally presented itself after a year's worth of driving. I just re-tightened the plug and it's not leaking any more. I think I will just leave it for now, and add the loctite when I change the radiator hoses soon for good measure.

DoubleO7

I am guessing the sensor has a pipe thread connection into the block.
I would be using teflon tape on the threads instead of locktite.

99er

Well it wasn't a leak from the coolant sensor. When I had tightened the coolant sensor the car didn't leak after running it. I suppose the leak was intermittent still, but I started noticing a coolant puddle forming again.

The leak was coming from the heater hose quick disconnect on the manifold. Apparently these tend to give out over time. I'm guessing this is a 11 year old part and just finally wore out. You can buy this part at the dealer for maybe $60. Alternatively the cheap fix: pipe at home depot, some new heater hose at autozone, teflon tape, and hose clamps. Special tool required: Pipe wrench.

Admosin

That's a nice looking engine block for being 11 years old, good job keeping it nice.

And a 60$ heater hose is a rip, no offense. they should be priced around 20-30$ if that helps you find a good priced one

in2pro

I second the kudos on the clean engine