How does the dealership do a coolant flush when the engine is still warm?

I'm at the dealership currently getting a transmission flush and a coolant flush on my 09 DCSB, and they said the wait time is 2 hrs.

2 hrs is definitely not enough time for the engine to cool down before cracking open the radiator cap or to drain the system. How does the dealership do a coolant flush when the engine when it hasn't cooled down sufficiently?

Also, for those who say DIY, I DIY mostly everything else except for the transmission since it's a sealed system and I'm pretty sure I'll screw up the filling processes that's detailed here on the forum, and the coolant flush, it would be too difficult to dispose of it in my area since I would have to drive 45 min to a haz waste disposal to drop it off. Not worth my time.

 

I flushed out and refilled my motorcycle while it was still warm. Didnt seem to have any problems.

 

Why wouldn't they be able to flush it while it was warm? When I worked at a shop we used to flush warm systems all the time. You don't need to let it sit for 5 hours to come down to room temp or anything...

 

How do you relieve system pressure? Do you only need to wait a short time for pressure to subside then you can open the rad cap? I drove 40 miles to get here so my engine temps were 190 when I dropped it off.

 

Modern radiator caps have a 'half notch' that bleeds radiator pressure into the overflow/reserve bottle. The tech will put on a set of welding gloves, turn the cap until it hits that notch, and release the pressure into the overflow tank. Once the pressure's bled off he can remove the cap the rest of the way.

It's still not recommended that you do it at home, because you can still get a blowback from the system if you're not careful.

 

Ah. Thank you. This answers my question. Gracias.

 

No problem; happy to help.

Your radiator cap is basically a pressure valve. They're mostly set for 15 PSI. Having the system pressurized raises the boiling point of the coolant by about 50 degrees (if I remember correctly) to make it more efficient. It can absorb more heat from the motor without flashing to steam that way. If the pressure exceeds that 15PSI the spring on the cap will allow the valve to open and it'll bleed the excess pressure into the overflow reservoir by letting some coolant out of the system. When you shut the car off and the system cools down, it creates a vacuum in the system that opens a separate valve in the cap that pulls coolant back in from the overflow, so your system doesn't run dry.
Turning the cap to that first notch basically just opens the valve manually.

Not that you probably cared how it functioned, lol. But I gave that explanation to customers in the waiting room many times when I was writing service for a shop, haha!

 

I liked the explanation. Thanks.

 

They have had that as long as I can remember and I'm getting really close to 61 years old.

 

Lol, modern is a relative term. But, lots of people still don't realize why there's two notches on their radiator cap.

 

Because they are experts at this?

 

Throw an old towel over the top before you turn the cap; it'll help keep the cap from popping off if it's damaged or you turn it too far. It also helps keep the hot coolant from getting on you if something does go wrong.

 

Wouldn't the thermostat be closed on a cold engine and now allow coolant to be flushed through?

 

Typically (in my experience, at least) a coolant flush includes a fresh thermostat. Our techs always used to just pull the old one before they started the flush.

 

Once you release the pressure off the radiator via it's CAP The coolant system starts to cool down fairly quickly You can start working on it in 10-15 minutes after that with no issues. IMO, The coolant flush and tranny flush are both DIY jobs unless you don't have the time and or place to do it.