Overheating problem

[devnull1260]

My '99 q recently started heating up, not to dangerous levels, but higher than usual. The temp gauge usually reads just under the halfway mark, no matter what, and lately I have noticed it will meander to about 20% over the midway mark if it is extremely hot outside, and especially in stop and go traffic. The fans seem to be operating ok, rad is clean, and there is no collapsed hoses, etc. I run 50/50 and just replaced all the coolant about 5 months ago (caps, thermostat and hoses too). It seems fine if I am moving along at a good pace, though once last summer the temp was > 122 outside and the temp gauge consistently showed higher than normal. I have about 78k miles on it, and it has been trouble free, until now, with the exception of a leaky turbine sensor.... which I still need to fix.

[elwesso]

have you replaced the Tstat?

[devnull1260]

Yup, I replaced the thermostat, the radiator caps, the hoses, and it has new coolant (5 months old) 50/50 mix.

I see no bubbles in the coolant, the fans are operating ok, and the hoses are not collapsing.

I'm not sure if this is something to worry about or not, since it does not get anywhere near the "hot" levels, but it concerns me that it moves at all once heated up to "normal" operating temps, it has never done that before, it used to stay just below dead center.... always.

[elwesso]

The only thing would be to see if the coolant is actually getting that hot... One would need a consult to verify.

[Q45tech]

Dirt, leaves, trash between rad and condenser?Bent fins on rad/condenser............rubber seal around rad?As new often requires new parts...................1999 is 8+ years old.

Never trust the inside gauge unless you recalibrate it with Consult so you know where the real 200-220F points are.

[devnull1260]

> Dirt, leaves, trash between rad and condenser?> Bent fins on rad/condenser............rubber seal around rad?> As new often requires new parts...................1999 is 8+ years old.> Never trust the inside gauge unless you recalibrate it with Consult so > you know where the real 200-220F pints are.

Thanks for the replies....

fins are fine and there are no leaves or anything. I took a look at the fan blade (the belt drive one), there are some very small cracks around the center hub, not on the blades themselves, looks like I need to replace that, but would that cause the temp to fluctuate that much?

[maxnix]

Are we talking OEM thermostat or some Chinese knock off retailed to you by a national automotive chain store?

Sytem purged of air?

[devnull1260]

I purchased the thermostat from infiniti directly, so it is the real deal. I am assuming that these minor fluxuations in temperature in high heat (105+) are not "normal" in the first place. Is that a fair assumption? In the past, the temp never varied... and yeah, I know the gauge may not be telling me the right temp.... but what is your experience with this? Should the temp remain constant under all conditions or is some variation "allowable"? As I said, the temp *never* gets much above the half way point, whatever the hell temperature that is.

also, it only varies in stop and go traffic, or right when i start up after stopping briefly, then goes back to the "normal" position once I get moving again.

And yes, the system was purged of air.....

[Skibane]

I sound like a broken record on this one, but...

Have you checked the fan clutch? They tend to develop more "slip" as they get older (resulting in less fan speed for any given engine speed). This causes higher engine temperatures when stationary or driving at low speeds. (Out on the highway, enough wind is forced through the radiator to cool the engine without any assistance from the fan).

You can test it by spinning the fan blades by hand (with the engine hot): The blades should stop spinning almost immediately - and there should be plenty of resistance felt when you spin them. If the blades continue to spin for more than fraction of a revolution, your clutch probably is no longer doing its job.

[devnull1260]

I think you are on to something skibane, i tried your test after running it on the freeway for a while, and in stop and go, it is certainly hot, (ambient was reading 110 from the street, i live in az).

Anyway, the fan spins almost 1/4 of a turn when i give it a spin, and there is very little resistance.....

the cooling fan has little cracks in the hub anyway, i may as well replace the clutch too.... thanks for breaking the record....

[Skibane]

If you replace it, seriously consider getting an OEM clutch. Just about every local auto parts chain has several cheap alternatives, but none of them are nearly as good as the original...

[devnull1260]

Will do. I have only used infiniti parts for replacement after I tried some crappy generic brake pads and learned the hard way.

I'll post the results, thanks again.

[devnull1260]

I installed the new fan and fan clutch today, and took it out for a rigorous test drive. temperature stayed put with no variation from just below center, the new clutch was noticeably more stiff, even when cool.

Thanks again for the help!