Loosing coolant. Underhood coolant smell

[Matahoe]

Buy contrast dye... put it in the resiviour. Also check you engine oil of you havent already.

then use a black light. Also pressure test with radiator tester, both hot and cold... you maybe able to simply heat engine up and look without the tester once it is to pressure.

How many miles are on your truck?

It has 202,000 miles on it. Bought it one owner in 2015 with 130K. The only thing rusted out is the rocker panels, torsion bars, a bit of the frame and all brake lines (that's another project).

It's been babied and garaged most of it's life but I have towed an 8000 lb RV and 4000 lb boat about 5000 miles in the past. 19 mpg at 70 mph. Lots of torque and sporty exhaust from factory. Man them stainless exhausts last a long time (knock on wood). Hehe. Kinda loathing I don't have Onstar service anymore. Was kind of nice. Last time I was at the dealer they said it was in extraordinary shape. I owe it all to you folks and your advice! She still runs like new considering I am in the rust belt...

 

[Matahoe]

You've a ship of Theseus that's about to hit its 20th anniversary.
Might be wise to consider which replacement/upgrade parts you'd like to either
have on hand in case of failure after 20 years, or
preemptively replace before failure.

I've witnessed coolant leaks so small, that a magnifying glass was needed to confirm.

Your knowledge of ancient Greek is impressive. I've done my fair share of replacing parts without adequate diagnosis. Can you please expound?

Thanks!

 

[Ken Casher]

Yeah that. I put my nose around the driver's side tank and that's where the smell is strongest. Looks like it might be time for a new radiator. But I'll check a few things before splurging. Any chance the coolant got into the oil or transmission fluid? I hope not. Thanks

I would replace the radiator. I finally realized that radiators go out between 200k and 300k. It's better to replace it now and be done with it. Mine failed at 270k when I was in the north Ga mountains with no cell phone reception.

 

[Matahoe]

I would replace the radiator. I finally realized that radiators go out between 200k and 300k. It's better to replace it now and be done with it. Mine failed at 270k when I was in the north Ga mountains with no cell phone reception

Wow! 270k miles. I wonder if it had been replaced before...say maybe around 175k? That's a long time. But I guess with proper coolant changes anything is possible. Never seen that with my previous 5.7 or 4.3 liter engine radiators. You're probably right. Time to invest in an appropriate preventative maintenance item. This wouldn't necessarily be considered parts swapping and she has been paid off for some time now. Thanks and I'll let you folks know.

 

[strutaeng]

Nah, probably not likely on the oil/water mixing. I've actually never had a radiator leak on me on the GMT 800 since I've had my 99 Silverado that bought in 2007. I only replaced it when I swapped the engine to gain the wider version. That was like 4 years ago. Original one had 260k on it. It did have a lot of gunk that was partially blocking the lower side.

My 06 Suburban radiator I think is also original (?) and has 262k on it. I bought that one with 225k, so not certain actually.

But they do crack on the plastic sides

 

[Matahoe]

you can do the free rental deal from a parts store and get a pressure tester that you leave the rad in and the system fully connected.

most common leak is the plastic side tanks on the rad. they just crack with age. its just plastic after all. thanks GM!

I think you're referring to a radiator pressure tester. I don't have one. I looked at the Mityvac kits and they are rather expensive with all the attachments and such. Last time I used a rental it looked iffy and abused by previous renters. I didn't trust it...but it did show it leaking down if I remember. But I attributed the loss of pressure to the expansion and then contraction of the coolant. That was about 5 years ago. Might be worth a shot to rent one again just to verify and I can provide the results. I guess I'm not confident about that kind of test.

 

[Matahoe]

I've had two difficult very small leaks in my coolant system to troubleshoot in the past 22 years. Both in the past 5 years. One was the radiator as described. The other was from the front steam vent crossover tube as described in this video:

Ok, I lied - I also had a water pump leak at the weep hole. But that one was quite obvious.

Hmm interesting. But I replaced the tube and o-rings some time ago when I did the head gaskets. The back side of the intake didn't have a tube...just a couple block offs which I replaced the o-rings as well.

I think the best course of action is to just black light the whole system, pressure test and replace the radiator if needed

 

[Matthew Jeschke]

@Matahoe you can typically rent a radiator pressure tester at your parts store. Note you may have to clamp off the resivour overflow hose depending on the pressure tester's design.

@Ken Casher 's suggestion to replace radiator is solid advice. It's only a matter of time till the plastic end caps break. Mine broke at 222k The radiator / plastic can form very small pesky hard to find leaks like you're experiencing too. Either way, it's lived it's useful life in my opinion.

Only regret when I changed mine not swapping in this "Cold Case" radiator. I there's quite a few complaints on them about mounting alignment. I think they're jigs at factory must suck or they get bent in shipping but from what I hear the tabs may need shimmed with washers for a flush fit. Not really a big deal. I recommended this to a friend locally for his build and he bought the radiator and liked it. I'd go with the one that has provision for oil cooler too. Cold Case told me I can leave it blocked off until the lines and oil filter / block adapter are installed and it'll work just fine. The part number is Cold Case GMT569A... It'll also give you some more capacity for trans cooling at same time.

 

[Marky Dissod]

I've done my fair share of replacing parts without adequate diagnosis.
Can you please expound?

One of my friends is still an NYC livery driver, driving a 2011 Lincoln Town Car that recently crossed
SIX HUNDRED THOUSAND MILES, on the original engine.

She's replaced more parts without 'adequate' diagnosis than any five of us put together.
She and her mechanics took educated guesses about how long things should / would last.
At 75,000 miles, she started replacing parts before they failed, based on those guesses.
Original engine, body & frame. 4th 4R75E rebuild, ATF drain & refill yearly.
3rd rear live axle rebuild - upgraded to 3.27 at my suggestion, her city MpG improved.

Since 2011, it's only been towed 2x, never due to a parts failure.

 

[Matahoe]

The part number is Cold Case GMT569A... It'll also give you some more capacity for trans cooling at same time.

I'm sorry. When you said "part number is Cold Case GMT569A" I was expecting a GM part number. Can you please rephrase that? I also have a local dealership gmpartsnow.com. It's Berger Chevrolet in Grand Rapids, Michigan. Largest Chevy dealer in Midwest afaik. They give me a veterans discount and no shipping cost if I pick the part up at the warehouse. Sometimes they (and a few other local GMC dealers) give me wholesale pricing depending on how nice I am, how expensive the part is, or how the wind blows. Lol. It's only a mile away from me. I get most of my OE parts from them. I can look up the part number on their website for sure. Just didn't know what you mean.

Looks like we are in the making of a GMT800 coolant leak encyclopedia! Good stuff for anyone to know. I will definitely keep everyone posted and report back here.