Hello, for the past 2 months I've had a cooling issue. After the engine warms up, the fans eventually turn on and stay on even at highway speeds. But the temp gauge stays below the halfway point (in 50-70 degree weather). Only on above 70 degree weather with the A/C on does it actually start overheating.

Regardless of any conditions though, the top radiator hose is friggin hot while the bottom hose is bone cold. AND the heater blows cold air at idle, but warms up if I rev the engine for a couple seconds.

So far I have:
- Replaced thermostat (tested old one, it worked fine)
- Replaced temperature sensor
- Pulled out radiator and checked flow with garden hose: very good (radiator looks new)


The only thing I can think of, is either a bad water pump, or worse, a leaking head gasket.

I don't notice any coolant loss, it's always full. I don't ever see oil in the coolant, or coolant in the oil.

Any ideas? Thanks!

 

this was happening to my 95 i put a brand new water pump thermostat all hoses upper lower and even heater hoses and still same problem i then changed my radiator and bam! problem solved the radiator was clogged!

 

Running water through a rad doesn't make it 'good'

If crap got in there or it got 'gelled' up from mis-matched or never flushed/changed coolant, then it could be plugged. on a bunch of the cross tubes, but stillf low water just fine. That doesn't mean it's sufficient for cooling a lot.

Do you have any codes?

You changed the CTS, you said? The fans shouldn't come on before the car gets to operating temperature. Regardless if the Rad or thermostat are bad, the fans shouldn't come on until operating temp unless your A/C is on and you're not moving fast.

But you did kind of say it overheats? BUT you say it doesn't get to temperature? Which is it? Please clarify.

 

When I checked flow with a garden hose, I stuck it in the bottom, and it came gushing out the top very quickly, and the same from top to bottom. Also, the radiator is very clean, and new looking as if it had been recently replaced. I hope you're right though, this would be the easiest solution.

There are no codes or check engine lights (according to my basic code reader)

The fans do not come on until the car gets to temperature, unless AC is on, then they are always on. The engine seems to always be on the verge of overheating. Just warm enough to kick on the fans but cool enough that it does not exactly overheat.

Again, the cold bottom hose on the radiator has me concerned. Radiator flow is fantastic, even if it were partially blocked the bottom hose should at least be warm correct?

And the heater, cold at idle speed and warm after revving. Are these symptoms of a pump that's not providing enough flow? Possibly corroded impeller?

Thanks for the input/advice so far!

 

Dude i can solve ur problem immediately, i just solved the same problem on friday!!

Read this entire post
https://maxima.org/showthread.php?t=645652

It solved 3 ppls problems this weeks.
Long story short, we bought aftermarket thermostats from different places and they didnt work, only a niisan oem thermostat fixed all our problems, the OP even changed his waterpump for nothing. Read it and get back to us. My thermostat hose was cold just like urs same exact symptoms

 

I tested the old thermostat when i pulled it out, and it worked just fine. Guess it couldn't hurt to try anyways. I'll pull mine out, and just leave the housing so there is open flow. If this works i'm gonna order a new OEM stat. Thanks for the tip!

 

Ended up reinstalling the old perfectly-working OEM thermostat. And guess what? It worked! Thanks to everyone for the help. I think what started my issues in the first place was faulty radiator fans, which I replaced AFTER the thermostat.

Who would've thought a new thermostat would be faulty and introduce a NEW problem to troubleshoot?

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That's funny. Very happy you got it fixed, and were able to do this yourself, well done dude.

FYI, Thermostats have 2 temp ratings, Start to open Temp, and Full open temp.

If one or both of these is out of OEM range, then the fans and T-stat will not 'read' each other correctly. The Tstat will allow temps to be higher/lower than the CTS wants and that will trigger the ECM to turn the fans on.

Sounds like this was your problem.

 

Let me be the first to say, I TOLD YOU SO! glad it worked out