SOLVED: Diagnosing/replacing a leaky radiator + flushing coolant (for the inexperienced GMT400 owner)

[slow_c1500]

Dumb question but is there a correct way I should fill the system with water to do the test? And to drain it when I’m done?

 

[454cid]

Dumb question but is there a correct way I should fill the system with water to do the test? And to drain it when I’m done?

Just through the radiator neck for filling, and for draining either pull the lower hose, or undo the drain if your radiator has one. The drains are not very accessible on our trucks, so I wouldn't bother.

 

[RichLo]

Dumb question but is there a correct way I should fill the system with water to do the test? And to drain it when I’m done?

Yea, fill with water and run the truck like normal for a couple weeks.

 

[slow_c1500]

I would only be filling it with water to pressure test the system, and simultaneously flush the block. Once I find the leak (most likely rad) and fix it, I will burp air and fill with green coolant. I don’t really have time to do a multiple-week flush.

 

[slow_c1500]

Couple newb questions: When I do the test, do I have motor off and have the test pump running at 15 psi? And also when I fill the system with water (to do the test) do I need to do all that stuff where you have motor on, fan on low speed high heat, or can I literally just fill the cap with motor off?

 

[Road Trip]

Couple newb questions: When I do the test, do I have motor off and have the test pump running at 15 psi? And also when I fill the system with water (to do the test) do I need to do all that stuff where you have motor on, fan on low speed high heat, or can I literally just fill the cap with motor off?

You've been given good guidance, but from the tenor of your questions this sounds like you are trying to
develop a new skillset. No problem, for once upon a time everyone in here was in the same exact spot you are.

****

So here's a quick description of how you are going to pressure test your cooling system.

Once you get one of the 'free rental' tools from the local parts store in hand (see attached for 1 possible choice)
you will top off your cooling system with water, and then connect this tool where the radiator cap normally
goes. You will then use this tool to pump up the pressure to ~12-15 lbs. (Look in your repair manual for what
pressure your truck is supposed to run and use that.)

Now the waiting game starts. Instead of a continuously running pump, we are actually going to give the system
a good leaving alone while looking for *any* drop in pressure. And the longer the system will hold the original
pressure that you pumped in without dropping, the healthier your cooling system.

For example, once I'm done with a build or repair session I would set the pressure to 12 psi, let it set overnight,
and if it was still in the same spot the next morning then it passed a confidence test for a 'DD level +' vehicle.

NOTE: A tiny weep might take an hour to lose 1 psi of pressure. Most small leaks will show a loss in 5 minutes or less.
And of course if you have a big enough hole in your radiator you will have a hard time madly pumping in order to keep
up with the pressure loss. (The silver lining is that kind of leak will be really easy to locate. :0)

For what it's worth, something that barely leaks and is hard to locate under zero pressure will usually become much
more productive/easier to find under pressure. By the way, if the pressure is dropping pretty quickly and you aren't
seeing an external leak, please be sure to check your engine oil level. If you've magically gained a quart of oil on the
dipstick then you need to drain the pan, confirm the failure, and then see what's going on mechanically with your motor.
Also be sure to check the interior to see if the heater core is the part that's let you down.

So if you are talking to a mechanic, knowing how long it took to lose how many PSI from the initial test pressure
will help the troubleshooting process. If the pressure is dropping ~1 lb every 30 seconds, then you and your onsite
mentor aren't going to be looking for a weepy/corroded freeze plug, intake manifold gasket just starting to go going
bad, etc.

But if you lose ~1 psi overnight then that's exactly the kind of thing you will be on the hunt for.

It sounds complicated, but really it isn't. If you have never troubleshot with a pressure gauge like this, it's always OK
to first prove to yourself how the process works on a known-good leak-free vehicle. (This goes double when using
rental test equipment, for you may have been handed a tired unit that would lead you down the garden path by showing
a pressure loss even on a perfect vehicle. (!)

As a matter of fact, if they bring you a really beat down rental unit, ask them if they have another one? Or thank them for
their time, and go down the street and see if their competitor has a better 'free' tester to use? Disciplined testing is
enough work without adding needless frustration from a bad tester to the mix.

And once you use the tester to locate the failing part (radiator?) make sure and use the tester again after you've replaced
the bad parts. A cooling system that passes the pressure test is a lot easier to burp & get back on the road.

Apologies for the length, but this is what I was taught by a mentor many moons ago. Except that he was talking and
pointing at stuff, where I have to use the keyboard remotely to share the same thing.

Best of luck finding & fixing your leak --

 

[Cadillacmak]

Hello all, the other day I noticed my truck was low on coolant so I topped it off at the overflow tank with some orange dexcool I had lying around. At the time I thought the existing coolant in the truck was compatible with dexcool, it was done by a shop a few years back. Turns out it actually had green coolant in it, and after driving it about 20 miles with dexcool mixed in there, I noticed a burning coolant smell. Popped the hood and saw that coolant had spat over the top of the engine. None of the radiator hoses were leaking, but the radiator was wet with coolant. I can only assume the mixed coolant is what caused this. I am obviously going to drain the system and replace with all green. My question is, should I replace the radiator? I see no other part that the coolant could have spat out of, but I’d like to hear any suggestions, or any kind of explanation for how mixing coolant can somehow cause this to happen. Thanks!

Check out this link. https://sharena21.springcm.com/Publ...2d889bd3/7e69eb8c-e29c-e711-9c10-ac162d889bd3
Dexcool was created to prevent aluminum corrosion (among other things) using organic acid technology (OAT). This is different then IAT or HOAT. So, no they are not actually compatible but they are mixable. For a you to get the benefits of each coolant, you need to only run that coolant. To put it in perspective, you can add organic 10-30 in your motor and it mixes with you synthetic 10-30, and then add some 20-50 and it mixes, but you no longer have the motor protection and performance of the synthetic 10-30.

 

[454cid]

Often the leak will appear before getting to 15psi.

Engine off.... otherwise your building heat and pressure, you don't want heat at this point.

 

[1998_K1500_Sub]

Yea, fill with water and run the truck like normal for a couple weeks.

I would never fill an engine with only water for longer than a day, and then I would try to drain it fully, or immediately backfill with antifreeze or an anti-corrosion additive (e.g., Red Line’s “Water Wetter”).

I did that once (ran water-only for 2-4wks maybe) in a new crate L31 and a bunch of rust particulates formed in the system. I’ll never do that again.

Purging them from the coolant system is a pain in the a$$ / waste of valuable time.
I have no idea if some particulates remain lodged in the radiator or heater core.

I’m pi$$ed to this day that I ever did such a thing.

Learn from my mistakes.

 

[454cid]

I agree water only for anything more than diagnostics or emergency is not a good idea.