Coolant replacement questions.

[lvermiere]

On my 07 12GT I just replaced the original special BMW coolant with the newest VW G12 coolant.

Temperature at highway and in town driving reads the same ( just over the second temp line in town when the fan kicks in)

The expansion tank has been reading between ther min and max mark level over a 3 ride period.

In testing 2 bars of pressure were maintianed for the required 5 minute interval.

My question(s)
1. If by chance I left a small residual amount of the original BMW coolant in the system will it be compatable with the VW coolant ( i.e will combining the 2 cause it to crystalize or jell?). How concerned should I be? When the temps really get up there do you think the VW coolant will do an adequate job?
If not compatable then either completely flush the system and replace the fluid yes?

2. How can one be completely sure that all of the air has been purged out of the system and no hot spots will occur? No air bubbles came out during the add/flush.
I've run the engine 3 different times and opened the top vents to remove any last trapped air. No bubbles at all in the expansion tank throughout this process.

Any last thought on how I can get some piece of mind on this? I was thinking of parking on a steep hill over night and then opening the expansion tank. The idea is that overnight any possible air would have worked its way to the highest point and could then be let off.

 

[kayakncycle]

Peace of mind comes with proper prep

You said: I was thinking of parking on a steep hill over night and then opening the expansion tank. The idea is that overnight any possible air would have worked its way to the highest point and could then be let off. Believe you think this because you've been around radiator systems for several years and know that air bubbles always work their way to the top. Well, they have changed the rules on us. Your GT and several automobiles have at least one nifty air trap designed in the systems. These traps work extremely well and will not move, i.e. no coolant flow. The recommended flush method is to use a vacuum flush system. You may purchase a UView 5500 for ~$100. Good money spent cause you will need it on your car someday. You use your air compressor to generate the vacuum.
Would have been prudent to check compatibility before mixing, but that's done, so lets move on. One could pour the two brands into a glass jar and watch it for a few days.
Or you could beg, borrow, buy a vacuum flush system and flush the GT a couple of times with distilled water before the final fill with your new coolant.
How much peace of mind do you need?
Dennis

 

[john1691]

I had my '05 K1200S at the dealer 3 years ago for a check after a light drop, had them flush and fill the rad. I asked how the new vacuum fill worked, they said it didn't, they use a funnel and fill the system. I wan't sure what to say, as I could have done that at home. 25k miles later, no issues. Not sure how I would know if I had "hot spots" anywhere.

 

[lvermiere]

I had my '05 K1200S at the dealer 3 years ago for a check after a light drop, had them flush and fill the rad. I asked how the new vacuum fill worked, they said it didn't, they use a funnel and fill the system. I wan't sure what to say, as I could have done that at home. 25k miles later, no issues. Not sure how I would know if I had "hot spots" anywhere.

Thanks for that John. It is kind of what I expected actually happenned at the dealerships. I did pressure test the system the required 2 bars for 5 minutes and i don't have any leaks so all is good.

I'm also thinking that the special ' engine ice' BMw coolant has about the same cooling capacity as the VW coolant I used so I shouldn't have any overheating problems.

cheers.