WTF is going on with my cooling system

[Modest Throttle]

I realize that there's many posts regarding overheating, I've searched and searched and none match my siuation.
My overheating problem is that randomly my car's temp gauge starts to rise, then goes down again. For instance, tonight at work (I deliver pizza) on a couple runs the needle started going up at slow speeds then went back down at high speeds. This leads me to believe it's the cooling fan, but that was just replaced 2 weeks ago with a brand new one. It only happened tonight for the span of about 45 mins, then the rest of my shift it was fine (I was driving pretty damn carefully at this point). I'm plannin on flushing the system, and replacing the t-stat soon. I popped the hood tonight on a delivery and looked at the resevoir and the coolant did appear to be less green than normal. I hope oil isn't leaking into it. Car still drives like normal.
any help is GREATLY appreciated

 

[DODej1]

Check for milky coolant, but if you had a bad head gasket the car would run horribly.

I would flush and replace the coolant and see how it works.

When was the last time the water pump was changed? The seal in the pump could have wore out and the coolant is coming from the weep hole, my old gsr did that for 2 weeks before it finally gave out all the way and leaked all the time

 

[Modest Throttle]

Check for milky coolant, but if you had a bad head gasket the car would run horribly.

I would flush and replace the coolant and see how it works.

When was the last time the water pump was changed? The seal in the pump could have wore out and the coolant is coming from the weep hole, my old gsr did that for 2 weeks before it finally gave out all the way and leaked all the time

The water pump was changed in October 2008 along with the timing belt, I don't think the pump is the problem but I suppose it's possible.
Yeah, I think the coolant is actually fine, I'm probably just looking at things that aren't there and blaming them but i'm gonna flush the system and replace the t-stat on monday or tuesday. My dad knows a thing or two about motors and he thinks that should fix it.
thanks for the suggestions

 

[oc_civic]

as ridiculous as this sounds.. did you replace it with a factory fan? is teh fan spinning in the correct direction?

 

[Modest Throttle]

as ridiculous as this sounds.. did you replace it with a factory fan? is teh fan spinning in the correct direction?

The new fan isn't OEM. And no I've never seen it running, but it's kinda hard to tell when you're sitting behind the wheel going down the road But I pulled over last night with the car running and popped the hood and the fan was NOT running for the minute or so I was checking things out. We're going to check the fan to make sure it runs when we flush and change the t-stat.

 

[chromal]

Could still be the head gasket. My 98 CX's head gasket started to go out this March/April with about 210K on it, passing exhaust gasses into the coolant loop. Maybe this was a result of damage from failing to replace the thermostat earlier, as it had become stuck open. Anyway, this exhaust leak caused the coolant overflow tank to actually start spilling over and/or blowing steam, but it was not a dramatic leak, just enough to over-pressurize the coolant system when you put the hammer down, say, on a large hill. This led to vapor gaps in the cooling system and random overheat spikes. Eventually, I could see white vapor clouds coming out the exhaust when I put the pedal down after engine braking some distance. Good news is, a new head gasket did solve the overheating problem entirely and it's still running well some 10 weeks and 4000 miles later.

Good luck, whatever's going on with yours.

 

[evilrilla2]

the way to see if your fan turns on is to open the hood, let the car running with the heater full blast, in 20 minutes, the fan should turn on. or to be on the safe side 1-30 minutes. so you should, flush cooling system, change the thermostat, and then park on a slightly sloped pavement, upward. let the car run like i said before, this way you bleed the coolant system and at the same time you get to see if the fan turns on. it should turn on 2x within 30 minutes. If all else fails, its the head gasket, check for white smoke in tail pipe, check spark plugs for coolant decay, check your oil for coolant residue. The faster you figure out the problem the faster you should fix it, if you run while ur car is overheating then you could severly mess up your engine. AND, you will not bring my Pizza on time!!! and you will have to give it to me for FREE!

 

[Modest Throttle]

the way to see if your fan turns on is to open the hood, let the car running with the heater full blast, in 20 minutes, the fan should turn on. or to be on the safe side 1-30 minutes. so you should, flush cooling system, change the thermostat, and then park on a slightly sloped pavement, upward. let the car run like i said before, this way you bleed the coolant system and at the same time you get to see if the fan turns on. it should turn on 2x within 30 minutes. If all else fails, its the head gasket, check for white smoke in tail pipe, check spark plugs for coolant decay, check your oil for coolant residue. The faster you figure out the problem the faster you should fix it, if you run while ur car is overheating then you could severly mess up your engine. AND, you will not bring my Pizza on time!!! and you will have to give it to me for FREE!

Haha now you probably just cursed me by saying that last thing! But yeah I tried bleeding the system a couple weeks ago but the fan never came on in the 35 minutes I had the car running. Did the incline and heater thing too, but my mechanic says it was running after he installed it so who knows. Like I said, we're going to test the fan tomorrow. As far as I know, no white smoke coming out exhaust pipe. And yeah I never let the needle get past three quarters. If it does I kill the engine and let it sit, but that's only happened with this problem once.

Could still be the head gasket. My 98 CX's head gasket started to go out this March/April with about 210K on it, passing exhaust gasses into the coolant loop. Maybe this was a result of damage from failing to replace the thermostat earlier, as it had become stuck open. Anyway, this exhaust leak caused the coolant overflow tank to actually start spilling over and/or blowing steam, but it was not a dramatic leak, just enough to over-pressurize the coolant system when you put the hammer down, say, on a large hill. This led to vapor gaps in the cooling system and random overheat spikes. Eventually, I could see white vapor clouds coming out the exhaust when I put the pedal down after engine braking some distance. Good news is, a new head gasket did solve the overheating problem entirely and it's still running well some 10 weeks and 4000 miles later.

Good luck, whatever's going on with yours.

Yeah I know it's still possible that it's the headgasket, but I'm hoping it's just the t-stat. I'm saving headgasket for last cause it'll be a b***h if that's the problem. Might as well take care of the easier things first and see if that fixes it.

 

[evilrilla2]

Also, based on my experience, DO NOT use HeadGasket sealer if it is the HG, I used it and it gave me more headache because it wouldnt work. I had to flush my system 3 times to get rid of it. I'm still waiting for the reimbursement BarsLeak promised me.

 

[2slo4u]

Also try testing your fan to see if fits even working by hooking it up to the battery to see if it turns on

 

[mikemo]

My civic was running a little hot off and on , what I found on my t-stat was black housing(plastic coating) on t-stat had come off stuck in stat not allowing to open or close all the way replaced no problems.And my upper hose was hotter and had alot of pressure on it ,my lower hose cooler without all the pressure .