1983 Z/28 with transplanted 87 305 TPI. When I pulled the engine out to replace a rusted through oil pan. I noticed fluid in the coolant - See Picture 1. By the color, i believe it is transmission fluid, making me suspect the transmission cooler internal to the radiator is leaking. Since I have the radiator out, I was thinking about pressure testing the internal transmission cooler. I planned on pressurizing the transmission cooler section with 20-30 psi of air and then see if the pressure gauge

Picture 1 - what looks like transmission fluid in the coolant

Transmission Cooler Port 1

Transmission Cooler Port 2
drops, which would indicate a leak. However, when I pulled the an fittings out of the radiator ports, it looks like the ports where set up for either inverted or bubble flare. It appears that the shop that put in the radiator used just 1/4npt to an-6 fittings. It looks like the seats of the ports are damaged - See pictures 2 and 3. Sorry about the quality of the pictures, they were the best I could get.

Is it possible to repair these seats in the ports, or is there a work around that will not leak so I don't have to replace a otherwise perfectly good aluminum radiator. It's been too long since the radiator was put in and the shop is no longer in business.

 

It's hard to see for absolutely sure what you're trying to show in the pics. Too blurry etc.

That said, those do look like SAE flare fittings in the radiator though. Hard to say how fornicated the threads are. ¼" NPT threads are also 18 per inch, butt of course, they're tapered. Won't fit right even though they'll screw in partway without much of a fight. Until of course they ... DON'T ... anymore.

HOWEVER... try taking a steel flare fitting or adapter of whatever sort of the right size (5/16", seems like most places these days list them by the threads, which are ½"-18) and screw it in there, tighten it, remove it, repeat, do that a few times until it threads in eeeeezzzy. After that a 5/16" inverted flare to 6-AN (I'll assume for the moment that that's what you've got) adapter should be able to go in there with some degree of security. Being nothing butt aluminum, the steel should be able to cut sufficiently serviceable threads in it. A single wrap of PTFE tape on the permanent fitting will lube the threads and help it go in sanitarily.

[mr_spock]Humans.[/mr_spock] Never ceases to amaze more logical beings like me how these epsilon double-minus semi-morons can DESTROY everything they touch, and think they're still doing OK.

 

Thank you for the advise, going to try that. I admit the pictures of the radiator are not the greatest. I can restore the threads most likely without any problems. Through the pictures are not the greatest, the inverted flare seats inside the ports appear to be chewed up a bit. My biggest concern is will these seal when I put an inverted flare to them. If I use another an-6 to the port size adapter, like what was done, will it seal properly?

If the old fittings did seal, don't remember sealing anything dripping from the ports when I disassembled everything. Where did the transmission fluid in the cooling system come from? Only place I could think of is through the transmission cooler inside the radiator. Once I get the threads fixed, I want to pressure test the internal cooler to see if there are leaks. If no leaks, then I am confused to where the fluid came from

 

Can't guarantee that, but looks to me like the odds are good. Being aluminum, just tightening a steel fitting in them, should flatten them out pretty good. To improve them further use a very thin schmeeeer of the Permatex/Loctite "high-temp automotive thread sealer w PTFE" on the seat during final assembly.

Can't answer that with any certainty. As far as pressure testing though, you can do that yourself easily enough with compressed air, as you propose.

OBTW - the threads for the flare are ½"-20, not 18. Sorry about that.

 

Using your advise, I used a 1/2-20 fitting and ran in a few times and it cleaned up the threads. Flared some tubing and used them to block one port off and attached a air line to the other port. Held 25 psi (air) for 15 minutes, 50 psi for 21 minutes and then cranked the regulator up to 75 psi which held for 31 minutes before I released the air. There was no pressure drop during any of these pressure tests. I am not sure of what the line pressure would be, heard around 25-30 but not sure about that. So unless there is a leak that opens up when the metal gets hot from the fluid, I am going to call the internal transmission cooler good.

I've seen leaks that open up when hot in the induction coils at work but those temperatures in those coils are around 2200-2400 degrees. Pretty sure that the transmission fluid does not get that hot, if it does I have bigger problems. I looked closer at the an fittings that was in the ports and they were just open on that end, looks like they were just plain old 1/4 npt to an-6 adapters, not a 1/2 -20 inverted flare to an-6 adapter The only scenario I can think is that when the radiator got replaced with the current one. The coolant system was never flushed out and it ha.s been there since then. It has been so long since that was done, I really don't remember the details of why they ran the an hose instead of using the stock lines (probably rusted out would be my guess or leaking). Thanks for the information and the advise!