Just went for a 5 hour drive from mile high elevation in Colorado to probably double that up in the mountains. I know from previous experience that major elevation changes can stress the cooling system. But my car has NEVER had any cooling problems in the 3 years I've had it, including many 30 minute 6000-8000rpm track days and driving cross country.

I first noticed the water temp gauge going up a little high to about the halfway point on the gauge; then it has consistently been reading low. Made it there and back ok..

*The LOWER radiator hose is cool.* Upper hose is hot. Expansion tank/reservoir is full, no noticable leaks anywhere. Heater blows hot, though possibly not as hot as it should.

94 B18C1 with 186k miles
Mishimoto dualcore aluminum radiator and OEM thermostat are 3 years/60k old. Coolant was probably flushed a year /12k ago when I put in a new OEM water pump.


Any ideas? I have to drive cross-country in a few days, need to make sure I don't get stranded!

 

Does the temperature gauge move depending on load?

 

I think it does seem to move a little under load.

Unless I hear any better ideas, I'm going to replace the thermostat and see if I can run water through the radiator to make sure it's not clogged.

 

surprised you didnt mention overheating, change out the thermostat, should work normally after that.

 

It's not overheating, at least according to the temp gauge.

So I replaced the thermostat with a new OEM one.. and still the lower rad hose isn't getting hot.
Heater is blowing hot air still, temp gauge reads normal now once the car warms up. Noticed the small coolant hose leading from the head to the thermostat housing (which goes through the hard line that the intake hose is connected with) is leaking a bit like it's got too much pressure.

I might try removing the thermostat.
Otherwise I'm suspecting a coolant passage blockage in the head someplace?

I don't get it, and I don't have the time or patience to spend much more time on this. grrrr.

 

tested both old and new thermostats by boiling in water = both were ok.

radiator flow seems ok; I dump water in the top and it comes out the bottom.

upper and lower hoses are ok, not blocked.

took the 1yr old OEM water pump out (PITA!), and it is ok, too. impeller fins are intact and it spins fine with the timing belt gear.

hard coolant line on black of block (from water pump to thermostat) is not blocked.


It seems like coolant is not flowing well enough from the radiator through the lower hose to the thermostat, but why? I'm completely stumped after checking all this.