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Fletcher0077 · 05-25-2020, 05:49 PM

I have drained radiator and pulled plugs on block. I'm changing all hoses and antifreeze. I got out 23.5 qts. Just what the book says. I believe still some antifreeze around water heater and small house heater. I will do a complete write up once I'm done.
My concern....I got to thinking all antifreeze is gone around the cylinder water jackets and the thermostat is still in. Once I fill the radiator do I simply start and add more coolant. Will the bypass hose provide enough flow the prevent damage to the cylinders? Is my worry misplaced? I there another way to do it? Thanks for your thoughts.

Skip426 · 05-25-2020, 06:54 PM

I'm not 100% sure if the GM t'stat on your engine is vented ( venting is accomplished with a SMALL hole in the t'stat with a float ) to slowly allow air out of the block . I'll see if I can get the info on the t'stat.
If you measure what you putting into the rad , don't start the motor until you have 80% +of the coolant in , because heated air in the block , won't open the t'stat and the temp gauge won't see the correct temps in the engine, unless in contact with coolant.

Fletcher0077 · 05-25-2020, 08:00 PM

I have replaced the thermostat in the past. It's just a standard stat, nothing fancy with a housing bolted on with 3 bolts. There is a short thermostat bypass hose which passes a small amount of antifreeze around the stat when it is closed. Capacity of cooling system is 23.5 qts. I drained 15 qts from radiator and 8 qts from the block (4 qts from each side via the block plugs.) 80% is 18.8 qts. The radiator doesn't hold that much.

TMyers17 · 05-25-2020, 08:15 PM

Are you familiar with a Coolant Vacuum Pump? It's the best way to refill coolant. It will pull coolant throughout the system leaving no air pockets. They are fairly cheap or you may be able to rent one.

dieselclacker · 05-26-2020, 09:30 AM

Remove the engine water temp sensor, fill until coolant flows freely from sensor opening. That should get you well past the 80% you are looking for.

Arch Hoagland · 05-26-2020, 10:49 AM

My procedure for changing coolant has always been drain the system and then fill completely with distilled water and then drive the coach about 20 miles.

I'd then drain it again and fill it with coolant mixture.

I never worried about the thermostat and left it alone unless there were cooling issues.

After the engine cooled down overnight I'd check the coolant level and add more if necessary.

I don't change coolant myself now because I no longer can get rid of it, back in the old days we just ran it down the gutter. Against the law here now.

Which brings up the point...what did you do with your old coolant?

Years ago on my first 8.1 in a 2003 GMC truck there was a known problem of leaking engine drain plugs. I had one replaced under warranty.

I'd never remove those for fear of creating a problem. The drain, fill and then drain again removes all old coolant.

Fletcher0077 · 05-26-2020, 10:18 PM

Arch I like your idea of drain, fill DI water, drain, fill coolant. To late now I'v pulled the plugs. Tapered brass plugs do look good and I had no leaks but will keep an eye on them. Pulled them with 3/8" drive 6" handle. Only had to grunt once.
I'm checking with the city for recycle centers. I believe any business selling automotive fluids should be required to accept old fluid. I know another regulation but some seem to make sense.

Dieselclacker pulling temp sensor seems like it will work. Also I have pulled the t'stat bypass hose....cuss,cuss,cuss what a bear on 8.1. I'm thinking I could add coolant through the block end connection point of the bypass. I believe this should go straight to the water jackets.
Another idea although I don't if it will work is to leave bypass disconnected for vent, fill radiator and see if coolant will back flow through water pump into block.

Wow, 3 senior members answered my post. Thanks for everyone's well thought out answers

US1 · 05-27-2020, 06:48 AM

I just did a full flush and clean on mine last week. Drained system, filled with water and Prestone Flush/Cleaner and put on 600 miles. Drained all again, removing block drains, lower rad hose and rad drain plug, along with all heater hoses. Flushed real good with garden hose till clear, then drained all again. Then installed all new hoses, leaving 1 heater hose open. Fillled with premix coolant thru the rad till full, funnel at heater hose to fill the lines going to the water heater and motor aid heater. All back together, filled the overflow bottle full, and then let the motor run to clear out air pockets. So far it hasn’t required more coolant. Used 6 1/2 gals to fill.
Have read all the recommendations of using tap water, soft water or distilled. Seems always was reason to not use one of them, so I just went the full premix method of the Dex-Cool and called it good.