I'm getting ready to start my first 3.4L rebuild/swap and have a question about the cooling system. The cooling system was completely dry so I'm concerned that I will have a lot of air bubbles trapped in the system. Since a break-in period of 30 minutes of non-stop running is required, I'm concerned that trapped air might work its way to the thermostat and not allow the coolant to flow correctly.

Should I leave the thermostat out during the break-in period?

What the recommend way to deal with the coolant during the break-in period?

Thanks,
Nick

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Nick D.
'88 Fiero GT 5-spd
'03 Jetta GLS TDI 5-spd

I never had a problem with my Fieros, I just filled the radiator thru the front cap, then put a floor jack under the rear to hold it up higher and filled the engine cap. I made sure the heater was set to max heat. I just left off the rear cap and started it. I stayed beside it so if it needed more premix solution, I was there to add it. After its run and temp stayed at limits, i tightened the cap and let it run a little longer, standing there and monitoring temp. Then let it cool down on its own a few hours. Then I open the rear cap only and check, adding if needed. Then take a short drive on the freeway, come back and let it cool again and recheck. With a regular car, I just run it with the cap off, then tighten it after its checked for level. I also test drive it a few minutes, let it cool and recheck. Lastly, I add any fluid to overflow to marked limit. Thats the ways Ive done them forever, someone else might use different methods. I do leave thermostats in for either case.

Thanks Roger,
So, you did this for an engine break-in period? You had someone inside maintaining engine RPMs at 2000 while you stood next to the engine thermostat cap?
If the rear cap was off when the engine was running at 2000rpms, didn't the coolant come out?
Was the thermostat installed during this time?

Sorry for ignorance, this is my first rebuild ever.

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Nick D.
'88 Fiero GT 5-spd
'03 Jetta GLS TDI 5-spd