My question is, are brass compression fittings on a mild steel line strong enough to effectively seal and hold tight enough for transmission line pressures? I'm now using a barbed hose end attached to a standard compression fitting to better lock the rubber hoses on the lines.

The history of the situation. I had just cut the end of my trans cooler lines near the radiator to add a plate cooler. I used a small line cutter, deburred the lines, flared the end slightly with a tube flaring tool and used the correct transmission/power steering hose and two EFI style hose clamps, as they don't tend to cut the rubber hose like the Hygear clamps do.

I had issues with seepage and even had one hose come off and pump trans fluid all the way to my favorite taco stand.

During Normal driving the 200R4 never gets above 160. It takes it a while to warm up to that too. It has a deep pan, one plate cooler and it goes through the radiator cooler first to help the fluid warm up for daily driving; and then through the plate cooler and back to the transmission.

When I do repeated drag passes 3 or 4 or more, the fluid temp climbs to 220 and will go higher if I don't let it cool for half an hour. In order to combat this, I am adding a second plate cooler and am plumbing 2 ball valves just before the radiator cooler.

I open the ball valve and close the bypass valve so the fluid flows through the radiator cooler first to get some heat into the fluid for daily driving days.

I can then close that valve and open the second bypass valve, so the fluid bypasses the radiator and flows only through just the plate coolers.

I'll follow up later and report on how effective this is on keeping my fluid temps under control.

25 years ago I installed them on my Road Runner, still there.
Doug

Cooler lines aren't at line pressure. maybe 5-30 psi. as I recall. My pick-up truck has been like this forever also.

Peace of mind. Thank you guys!

I thought they could spike momentarily to 90 psi or more shifting into reverse. I was told that was why it was never a good idea to use the rubber hose kits that come with most coolers on a Torqueflite.

In any case a compression fitting is adequate to hold any pressure that might turn up in a cooler line.

Kevin

They can be used for brake lines too...which is high pressure. They can be a pain to do right..but they work.

I have used them on transmission lines , gas lines and also brake lines with no problem. On the brake ;one, it was a quick fix until I replaced the the rusted line. I would say the brake line is probably not a good long term fix .

Check dealers for thermal bypass valves - they may be cheaper or same price as two valves and you wouldn’t have to play with the valves. Set it and forget it.