I replaced my radiator earlier this summer with a remanufactured stock replacement from NAPA and have a strange cooling issue. If I drive around town or even on the freeway in rush hour the car doesn't get hot, it stays around 1/2 way. If I get on the highway and drive 75+ the temp starts to go up? It's been pretty hot here in AZ but no hotter than previous summers and the only thing I've changed on the car other than the radiator is the rear diff. I swapped in a 3.69 VLSD last fall so the engine is at about 3000rpm at 80 mph. I've bled the system multiple times, it doesn't ever seem low or pull from coolant the reservoir and the heater blows hot. I even bought one of those funnels with the radiator cap and ran the car waiting for a big bubble to escape but it never happened and the car never got over 1/2 way up the temp gauge. My car is an early 04 so it has a mechanical fan, could the clutch be the issue? or did I get a **** radiator?
Thanks

 

...got the same problem. everyone's saying blown head gasket for me. Absolutely no DIY on this forums for a head gasket unfortunately!!!!

 

Have you changed your coolant temp sending unit? This doesn't necessarily sound like a head gasket if you aren't losing coolant.

 

may I ask where the coolant temp sending unit is located @? I've asked on your other thread as well. thanks for the info!! I really appreciate it
actually i might have found it... can you confirm with me this is the one you are mentioning? #4

http://www.nicoclub.com/FSM/G35/Sedan/2003/co.pdf

 

Could be something simple like the lower radiator hose collapsing under high pressure - typically happens when you're under load at higher RPMs, and not necessarily something you'd notice if you were mostly stuck in traffic around town.

 

Thanks, I'll give the lower hose a shot.
I don't think the sending is relevant to my car since it has a mechanical fan.
Definitely not a head gasket, coolant is always at the cap and the reservoir level doesn't change.

 

I'm updating this for anyone else that has a similar issue. I fought this cooling problem for over a year, I changed radiators (warranty), hoses, belts, bled, re-bled, re-re-bled (...) the cooling system more time than I can count, did leak down and compression tests, everything you could imagine except change the thermostat, turns out, it was the thermostat, go figure. anyways, I hope this helps someone down the road.

 

Thanks for the update, Peoria! Nice to see another g35 in phoenix, let alone Tempe. I have an 06 sedan, you have any goodies for me by any chance?