RB20's can the lower rad hose collapse?

[Cpt_Impossible]

I have been struggling with an overheating problem strictly at freeway speeds for almost a year now. I have tried just about everything but if I dont blast the heat and take it really easy, the car will overheat at freeway speeds. Yes, I know that it is overheating because it has topped out before and spewed fluid. Also, I can see the fluid level raised int he resivoir after a freeway drive. The car has no problems blasting around the streets, but the continual 3k or so on the freeway just kills my engine. I have tried:

System is fully burped, does not require any filling after drivingUpper rad cooling panelLower Rad Cooling PanelNew Radiator CapNew ECU temp sensorNew OEM ThermostatTwo 12" E-fansCutting out the pignoseHonda OEM coolant with distilled water and water wetterKoyo Radiator

I recently took it to a shop and they said that the pump and headgasket tested out fine, that coolant was flowing just fine (as evident by my blazing heater) and they thought the FMIC was just blocking too much air to the radiator so they had me cut out the pignose. Ive done that now and there is still a problem. 90% of the air that hits the fmic has no other option than to go to the radiator because of the upper and lower cooling panels I have added and at freeway speeds, I would think with all the ducting the radiator should be getting plenty of air. And besides, the car overheated on the freeway with the side mount intercooler I had too.

So I got to thinking and searching and I found that a lot of other cars have overheating problems when the lower radiator hose gets old and soft and then collapses under the vacuum created by the pump's constant sucking at freeway rpm's. Most manufacturers seem to install a spring inside the hose to keep it's shape under these conditions. My lower hose is soft and I was wondering if this is a feasable cause of my problem. I am thinking of getting a Mr. Gasket SS ribbed hose to replace mine because I think gettign an OEM one will be a pain. The appropriate length hose from Jegs though is around $60 and I dont want to waste the money if my theory is flawed.

Any thoughts?
Modified by Cpt_Impossible at 3:31 PM 3/30/2007

[DJButton]

I have a metal spring type lining in my upper rad hose, I needed a new hose anyway and you can purchase multiple lengths at your local parts store, (Advance Auto Parts in my case) Cost me like $9 or something with my dealer's discount, worth it in my opinion. I also replaced the lower rad hose with a similar shaped molded hose. Even without the metal wire just putting a new hose on should fix the problem of compression due to older weakened rubber.

[Sil240]

Hey Try taking out your rad and taking your hose on full blast and cleaning out the rad.

I know my Block had rust in the water passages.

(PSA..... Do not use Straight water even if your in a hot place. It's a Iron block It'll rust like a Mofo)

I'm assuming you have pressure in your rad and your cap is good. Because you said that it spewed fluid. (guessing from your overflow bottle.)

Change your HO-ses and your check your Rad Cap pressure.

[uber95]

"Burp" the system. Air pockets trapped in the system can cause overheating. There is a 10mm bolt on the square block on the factory intake in the front on the top, right above the fuel rail. crack that to let any trapped air out. I don't have my camera or I'd post a pic of it.

[Cpt_Impossible]

Yes, I know about burping and the koyo was added recently so it isnt clogged, it is still gleaming.

[Sil240]

thats crazy....What the hell can it be??If your have a good rad,twin fans, ducting, good thermostat, and good flow through the block. I dont get it???

Wash out the rad from the opposite ditection.It'll take up some time but thats about it.

[Cpt_Impossible]

Quick Question...

Which radiator cap should I be running? the KA one or the Z32 one? The 300zx one is a higher pressure cap than the KA. Right now I am running the KA one is this correct?

[Cpt_Impossible]

A quick reference for the caps is:

KA24DE: 13psi 0.9BarVG30DETT: 16psi 1.1bar

Nismo, Greddy, HKS, Power caps 18.5psi 1.3bar

Question is, what is the RB20 supposed to use?
Modified by Cpt_Impossible at 1:10 PM 3/31/2007

[Cpt_Impossible]

Answered this one myself, according to skylines australia the KA .9 bar one is the correct one.

[Abdo]

i recommend a nismo low temp thermostat (only $60), it opens at 62 degrees C (169 degrees F), while the oem thermostat opens at 76.5 degrees C (195 degrees F)

i had that same problem with my KA-T setup, but it only overheated after 20 minutes of idle instead of on the highway.