Radiator Cap and Overheating

[Lextreme II]

This is very complicated but i will try to explain this event. Recently I upgraded my LS400 radiator to a Supra TT (Koyo) with 2" thick. The stock radiator doesnt have a cap in it. The cap is at the reserve tank. Anyway, the Koyo radiator doesnt come with a cap. So, in order for the car to run it will need two caps. One for the radiator and one for the reserve tank.

The radiator was filled with a combination of water and a gal of the red radiator fluid. I make sure there is not air bubbles. The car kept over heating and overflowing of the fluid. I kept refilling the radiator and change out the cap from the stock pressure of 13 psi to 16 psi. The problem still occurr. I switch the caps from reserve tank to the radiator and vice verse, but still overing and overflowing.

Change the thermostat but the problem still not going away. So what I finally did before switching back to stock was to modify a cap and delete the spring and seal. Basically I just want the radiator to cap it off and allow free flow of water from and to the reserve tank. The overheating problem solved.

This is an experience I would like to share with you guys. For the past few days this has been giving me hell. Just a cap can cause so much problem.

 

[Toysrme]

Exactly. Several of our systems use a dual cap system also, and I always have people change them. The problem for us is very common. Toyota/Lexus decided that the no cap system was better. That's fine, fewer parts & all. Then they turned around & refferanced the new radiator as our replacement radiator. (and it still is).
So every few months I run into someone overheating that's had a radiator, cap & thermostat change. Has good compression. What's the problem??? Someone put in the "wrong" radiator!

When you figure every psi increase you have raises the boiling point 3.25*F. That can be huge once you add it up.
You start going from 13-16psi stock caps to 19-21psi caps. You're talking 9.75*F to 26*F changes in boiling point.

Off a "nothing" part LoL!

 

[Lextreme II]

Anyone know if the Lexus LS400 take S-typ or N-Type cap. I know the Supra TT radiator cap would not work. Its too short (seal). I have seen some TRD caps with 21 psi. I think the seller gave me the wrong radiator. OEM Supra TT cap would not work. I think they gave the 7MGTE radiator. Secondly, anyone know where i can get a cap without spring or seal. I just need some to cap off the radiator.

 

[Nick M]

I think pressure cap placement has more to do with a high spot.

 

[1uzvl]

i dont know about you guys in the US but from memory the 2.8 turbo diesels Nissan Patrols have a blanking cap on the rad and a normal cap on the side header tank if that helps.