Overheating problem.

[craaaazzy]

Hi guys,New guy to this forum, great place for information. I have searched and have read all i could about the issue but am still a bit confused.

Here's my problem. Car starts to overheat about 5 minutes into driving, the needle goes up near the H, never gets to the H, but then goes back down to normal if still moving. If I am moving at a slower pace, say 10-25 mph, then the needle goes to about 3/4 - 7/8 up and stays there until i start going at highway speed again (60 mph).

i have done a full coolant change (coolant was brownish in color with only maybe 5 drops of oil in it), flushing the system twice. i have changed the water pump, the thermostat, and radiator cap. i thought maybe my head gasket was the culprit but after a compression test, all seems well (160, 168, 162, 160). also no signs of coolant in the oil.

do i still have an air bubble in the cooling system? should i also replace the radiator?

oh, i've got a 93 240sx w/ 156k miles on it.

funny thing is that i had a slight hesitation problem between 2-3k rpm's which i had tried to solve by new cap rotor, wires, plugs, fuel injector cleaner but nothing seemed to work but after flushing the cooling system, no more hesitation...??? car was also stalling out previously but no more of that either.

any help would be greatly appreciated. tia!

fred


Modified by craaaazzy at 6:07 PM 5/31/2006

[teddy]

I don't have a definite answer for you, but it could be that you still have an air bubble(s) in the coolant system somewhere, or youv'e got some blockage somewhere, whether it's in the radiator or coolant passages somewhere.

Also, is oil still mixing in with coolant after the change?

[craaaazzy]

i just editted my first post when you replied...but no, no coolant in oil.

another weird thing is that my gas mileage was terrible before the flush but much better afterwards...

[GIsvt]

Do you have a E-fan? sounds like the fan might not be rotating until it get hot enough. Could also be a stuck thermostat.

[RPS13.5]

try to replace the thermostat...maybe it doesn't open up until it gets really hot. Get a Nismo thermostat.

[stonybrookadam]

This is a classic fan clutch problem. Basically, you're not getting enough airflow through the radiator when sitting still. You have a little at medium speed, and enough passive flow (no fan) at highway speeds to keep your coolant temp down. Between the water pump and fan is a fluid clutch that senses temperature of your radiator (or water pump, depending on how you look at it). When this little guy dies, a couple of things can happen-- The fan is "disconnected" from the belt, and moves relatively slowly. This will cause overheating. The fan is ALWAYS connected, and sucks HPs from your engine.

If I remember correctly, the clutch disengages around 2000 RPMs, so you fan doesn't go completely haywire.

I just replaced my fan clutch with an aftermarket (~75usd), and all of the above problems went away. I'd be worried about "a few drops of oil" though, unless it was just a transient leaking from your overheating engine... The replacement is easy, and doesn't even require a coolant purge.

[nightkid86]

Try bleeding the system with the heater on full blast...to me it sounds like air in the system.