I wish I'd read this thread earlier. Since the problem is happening on the freeway then you can rule out the fans. Some of the ECUs don't even turn the fans on above a certain speed as the airflow from driving that fast should push more CFMs of air through your rad anyway.

The behaviour you describe is similar to air bubbles being in your cooling system. I have replaced hundreds of thermostats for being stuck open or leaking (car never heats up properly). I have only ever seen one that was stuck closed and that was the fault of the DIY mechanic who touched it.

If you've already burped it then it seems likely that it's a headgasket. Sometimes if you start with the car cold, remove the rad cap (make sure it was cold first). Then rev the car and see if you end up with either a geyser of prestone or a continuous stream of bubbles. Either one is a simple way to show a severely compromised headgasket. It could still be the HG but that is a simple way to check.

-Michael

 

Excellent suggestion. Sounds like the headgasket to me, youve exhausted all the other possibilities aside from that and a line blockage. How many times have you flushed it out? Did you get the proper amount of coolant on the drain, so there isn't any blocked up anywhere? That is highly unlikely, I would pursue the headgasket first.

 

It has nver been flushed out. I'll try reving I with the cap off after work tomarrow. I'll keep everyone posted.

 

Well I took the cap of and reved it and the coolant seemed to overflow out of the rad when reved harder. So I'm assuming this is the gyser you were talking about?

 

Well update, while driving round trying to fiNd a motor manual that I can't find lol the car heated only goin uphill but didn't heat like befor it only spiked up slightly then went down. No longer heatin on freeway

 

Well on the drive over there was no heating. Were doing a pnp on the intake and installing a pigg so we looked for all the signs of a bad head gasket non are there my friend seems to think there was air in the lines. Not sure only time will tell I guess

 

never seen a headgasket go bad in a japanese car this early in its service life, only on american cars, so if the headgasket is really bad i'd be pretty surprised.

 

Well I havnt had it heat since we did the work today. Bu on a side note after he port n polish of the intake mani and the install of he piggy I'm throwing a p0069 code. As well as the p0171 cod I've Been throwing since forever. Any tips on this? Car seems to run fine. Pretty nice noticable gains but now these codes.

 

p0069 is MAF sensor, no?

 

Says map/barometer I think

 

P0069 MAP-Barometric Pressure correlation.

 

On a stock car it means your MAP or your ECU are bad. If you've installed a piggyback then that's probably the issue. I think the 0069 needs a minimum of 3-4 cycles before it trips and the measured tolerance is very very close - about 0.1v.

Some minor overflowing of the rad is normal when you rev with the rad cap off. Coolant shooting up 5' in the air is not.

-Michael

 

Try getting your radiator cleaned or replaced, some shops disassemble the top plastic tank and use a thin steel line to removed clogged stuff from the lines, pretty cheap and the radiator works as new. Also another suggestion check the air passage behind the rad., one time a friend of mine got a serious problem with overheating and when he removed the radiator there was a plastic bag in front of the A/C condensor so the air was not really passing thru at all.

 

Well we burped the system real well like way better than after I put In the new ther
and so far so good. As fr the cel I think the piggy is making I throw but the performance is amazing on it it's not causing it to run bad.