Transmission cooling line leaking at radiator after rad replacement.

Asked by Jun 25, 2015 at 09:03 AM about the 1997 GMC Sierra 1500 C1500 SLE Extended Cab SB

Question type: Maintenance & Repair

I replaced the radiator in my 97 GMC Sierra
yesterday and after a short test drive I see a
lot of transmission fluid all over the place
under the upper fitting. How does one go
about getting a proper seal on that fitting? It
looked like a flange fitting, and I was very
careful to not cross thread or strip the fitting.
I tightened it to a firm snug on both. Am I
supposed to have used a thread sealant?

3 Answers


You shouldn't need a sealant, I use Teflon tape on my lines and has worked well. You could also use Permatex High Temp sealant.

1 of 1 people found this helpful.

I've used both and they work to give you that seal you want.

I actually got it to seal by backing off the nut and jiggling the line and I guess I got a better seating the second time around. That problem is solved. Now I'm seeing a small amount of coolant below the filler neck. I'm guessing I should replace the radiator cap as it must be where it's coming from?

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