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

[JDGMC]

My manual says to add them. But idk if I should trust it because it is assuming you are using dexcool, and I am using orielly green.

If I did need the tablets, is it ok to add them a few days after filling it with coolant, or do they both have to be added at the same time?

You don’t need the tablets and I strongly suggest not to add it since they will contaminate your coolant. The tablets are used for addressing leaks. Sealing tablets or liquids are generally comprised of silicate, metals and fibers and the GM/ACDELCO version are walnut shells, ginger root and binders. If you're worried about left over water/coolant - check the coolant voltage potential between a ground and coolant from time to time with a digital volt meter. Probe to a good ground and place the other probe in the coolant without touching the filler neck. Should be near 0-.1 with a a clean flush and new fill depending on the type of water used (DI will be the lowest). The limit is around 0.3. Anything higher may indicate the electrolysis inhibitors aren’t doing the job or coolant is out of balance causing accelerated electrolysis. It’s all about the stoichiometry for the various brands, what they chemistry they chose and how much of it they add to their formulation. They are not all the same! Diluting or concentrating with other antifreeze brands, losing water or adding too much coolant (antifreeze contrate) can degrade the inhibitor chemistry even though you have the correct PG or EG ratio for freezing temps. There are inhibitor test strips based on type of inhibitors used. Some brands offer strips for their products so that would be the way to go for accuracy.

 

[slow_c1500]

Awesome thanks for the info. No tablets then.

Would my method of filling block first, rad second be better than just filling everything by the rad?

Also what about the air that will be the trans cooler lines?

 

[JDGMC]

Sure you can. Fill the block first and button up the system then fill from the radiator. Just be ready to add when the thermostat opens up. If you follow the procedure in the service manual that's all you really need to do. Unless you lost a butt load of fluid, the trans will purge itself when you go through the gears - then check fluid. Don't fill it to the mar. It needs to be hot for the final top off. Hot is not just engine temp - it needs to be driven. Again, follow the service manual and you'll be fine. Will the truck be sitting for some time or is this a daily driver?

 

[slow_c1500]

It is a daily driver.

How do I tell when the T stat opens, and how much longer after this point do I have to run the engine to burp all the air out of the coolant?

And when you say it has to be hot for final top off, you are referring to trans fluid, correct?

 

[chris032188]

A tip ill give you - Drill a small hole in top of the thermostat (in the flat metal portion of it). Itll help the air bleed out. I just did this, kept having air bubbles causing my system to bubble over. This help tremendously. I did this, filled radiator, filled reservoir. Let it idle with cap off for about 10-15 minutes. Kept an eye on radiator level and the reservoir tank level. Slowly revved it to about 2k-2.5k and held it there for a couple minutes. Shut her down, put radiator cap back on (I'd put a new one on if you were spraying out of last one). Restarted let it idle, and watched the temps from the gauge and IR gun. Once it seemed good at idle, I revved it again watched temp rise and come back down a few times as T - stat opened up. After that filled reservoir and took it for a ride.

 

[rebelyell]

I’ve been flushing the block for hours now and I’ve gotten the water itself to be clear but it always has some small amounts of rust bits no matter how long I do this. Is it very important that I get every single last bit of rust out? I mean it’s been way dirtier in there for 28 years and the truck has never had problems with overheating. Should I be worried about the little bitty rust bits in the bottom of the block or no?

neither you, me or anyone else will get that rust and sediment and scale out by simply flushing a lot of water through it. That job requires a real Cleaning. AFAIK, there are only two ways to Clean it.
1) total engine disassembly and having a shop either Vat OR Bake & Blast the block & heads; that's probably Not practical here.
2) With a running motor in frame, you can DIY Clean its coolant passages by using a Strong Chemical Acid. GM published a TSB on this about 1999; I don't recall its number but you can google that as well.
You do a search for Oxalic acid, DAP Wood Bleach, discontinued Prestone AS100, discontinued GM 12346500. That procedure WILL DISSOLVE the rust & sediment & scale that coats entire system. There's a long procedure that I'm NOT gonna drag out or write up --- YOU google and find it. It's a Strong Acid and Requires Eye protection and Rubber Gloves. Told ya. Also, the stuff on parts store shelf today is Not strong enough. Told ya.


here's a helpful link with that TSB spelled out

Best cooling system flush chemical? - Page 2 - Don Terrill’s Speed-Talk

 

[JDGMC]

It is a daily driver.

How do I tell when the T stat opens, and how much longer after this point do I have to run the engine to burp all the air out of the coolant?

And when you say it has to be hot for final top off, you are referring to trans fluid, correct?

The coolant level will drop when the thermostat opens. In addition if you have a working temp gauge you can watch the temp go up to approx. 200 or so when the engine is warming up and then slowly drop in temp below 195 as the thermostat opens. Install the radiator cap and let it run for 10 min or so. Look for leaks and feel the top and bottom radiator hose to confirm they are indeed hot before you take the 15 mile drive to check the level of your trans fluid. Keep an eye on your temp gauge while driving. When all this is completed check the coolant level again when the engine is cold.


GM Manual

Coolant Fill

• Check the radiator drain **** to be sure it is closed.
• Check the engine drain plug to be sure it is tight.
• Premix the antifreeze with clear water in 50/50 mixture.
• If the old coolant is being used, check it for glycol/water mix of 50/50.
• Place a large top funnel in the radiator fill hole.
• Slowly pour in the coolant. The filling may be slowed because of the thermostat being closed.
• After the cooling system is filled to 1/2 inch below the fill hole, start the engine and let the cooling system warm up. When the thermostat opens, the coolant level may drop. If the level drops, add cool ant until the level is up to the fill hole.
• Replace the radiator cap.
• Check the coolant level in the recovery tank. Add coolant if needed.

Transmission Fluid Checking Procedure

• Warm the transmission fluid to operating temperature by driving the vehicle about 15 miles (24 km)
• Operating temperature is 180-200°F (82-94°C).
• Park vehicle on a level surface, place shift lever in “P” park and apply the parking brake.
• Check fluid level on the dipstick (read the lower level).
• If fluid level is low, DEXRON ®-III Automatic Transmissions Fluid is preferred, if unavailable DEXRON®-IIE is acceptable, add only enough to bring the fluid level in to the hot area.

 

[JDGMC]

Slowly revved it to about 2k-2.5k and held it there for a couple minutes. Shut her down, put radiator cap back on (I'd put a new one on if you were spraying out of last one).

Be careful when running the engine at higher RPM without the radiator cap on. A good amount of hot coolant may burp out of the radiator fill neck when going back to idle or off.

 

[Erik the Awful]

There's no need to pre-fill the block and then fill the radiator. Just park the truck facing uphill and fill the radiator.

I do highly recommend the Lisle coolant funnel.
www.amazon.com/Lisle-24680-Spill-Free-Funnel/dp/B00A6AS6LY

 

[slow_c1500]

Since I flushed it while the truck was parked on a slight incline facing uphill, should I be worried about water being in there that never drained out?