Why is my engine overheating?

[Lurkable]

(This is on a stock KA in 95 s14).

Last night my engine overheated and I noticed two things:
1. I was extremely low on coolant
2. The radiator-to-engine hose was loose where it connects to the radiator, and coolant had been evaporating through there.

So I pushed the hose back on all the way and re-tightened the clamp, and filled up the coolant reservior. I didn't really know how much coolant I had lost but I filled up the reservior once and barely made it home after stopping about 5 times to let the overheated engine cool a bit. At home, I filled up the reservior 4 or 5 more times, each time the reservior was drained (to the engine I hope - I didn't see anything leaking on the ground).

So I get home and begin to investigate. Here is what I found:
- Both coolant hoses INTO and OUT of the radiator are HOT (thermostat must be working)
- Both fans are WORKING (I can see the e-fan spinning down after turning the engine off)
- Heater in cabin blows COLD air half the time (this part I don't understand...)

I don't understand why the heater blows cold air when the engine is overheated and the car is running sometimes...I know there's enough coolant in the system now because the last time I filled the reservior to max and drove it around, I came back and there was extra coolant in the reservior. At this point the only thing I can think of is air bubbles in the system from when that radiator hose was loose, although I'm not sure how that causes these symptoms, but I guess I'll try running the car with the radiator cap off and squeeze those hoses to dislodge any bubbles.

If anyone has any other ideas...please let me know. I have to leave for work in 30 minutes and I'm freakin out!

[Grenade180sx]

... first thing is when the car is cool. fill at the radiator. not the res.

your heater hoses will either blowcold air because A. they are hooked up backwards. or B lack of coolant.

FILL DIRECTLY INTO THE RADIATOR ITSELF NOT UR OVERFLOW. blast your heater as your filling it up then start the car and let idle up operating temp

[MELLO*SOS]

You need to bleed the system otherwise you'll have some air in there which will cause you to overheat. There is a bleeder screw you need to open up as you fill the radiator (NOT the over flow tank), keep filling until water squirts out of the bleed screw. Then replace the screw, rad cap and refill your overflow tank halfway.

Like the guy before said, run your car with the heater on, let it cool, bleed/fill, then go for a drive around the block to get back up to operating temp. Let it cool enough, check the coolant level and re-bleed if needed. Sometimes you have to do this cycle two or three times to get all the air out.

GL

[pignose4life]

is there white smoke coming from exhaust?
it might be the headgasket check the oil if its light and creamy most likely it is.

[civilized_drifter]

why in the hell would you fill the resivor?

[Lurkable]

I thought the reservior was an overflow tank/fill point. :-/
No smoke in the exhaust.
Thanks for the help guys!

[ericcastro]

if you are too lazy to find the bleeder valve, or are having a hard time. then fill the radiator up, leave the top off, and turn the car on. Watch the water in the radiator.
Are there airbubbles coming up?? or is it just coolant rippling from vibration??

Usually for me, I do this method. its not quite as surfire as the other system, but it works for me.

I also squeeze the radiator hoses, giving them a couple pumps to push any air up to the top. Once your radiator stops pushing up air, and its topped off, put the cap back on.

do so on a cold engine too.

PS, this is more the way that you would carefully refill an overheating engine when you are just trying to limp a car home.

[kcndizzle]

Yeah like everybody else says, jack the front of the car up, fill until it pours out the top, top off the overflow, close the cap, and open up the bleeder screw. Last time I bled my s14 it took like 15 minutes on idle to get it properly bled. So just take your time with it.

[g6civcx]

Check heater hoses. Mine leak and I was losing coolant = overheat.

[wonkuuzenki]

Remeber when you do take the cap off to let it run Jack the front end up as high as you can off the ground. Helps the air escape.

[used240sxparts]

ya, or just put your car on an incline or hill...

[Lurkable]

Rock on guys! I think I fixed it, I just still have a couple questions mixed with a little commentary.

So all I have at my apartment is the stock jack for the car, which I don't know if you can even use anywhere besides the 2 jack points on either side of the car, so I wasn't going to bother with that. Also, I live on a steep hill, but there's nowhere on the street to park in a good position so I just did this on level ground in the parking garage.

I removed the radiator cap, stuck a funnel in it, turned the engine on, turned heater in cabin to HOT and fan to 4 (full blast), unscrewed the bleeder screw and let it run for 15-25 minutes, and squeezed the top hose a bit. I'm assuming the most likely place for air bubbles was the top hose which was the one coming loose from the radiator. (Also, anywhere else is impossible to stick your hand down there an squeeze.) I really don't know though...could the bubble have travelled anywhere throughout the system by now? I only poured a little bit of coolant into the radiator at this point - it already looked full, and the reservoir was half full.

For future reference: is it better to remove the bleeder screw completely when you're trying to get air bubbles out through there, or just unscrew it a little, or a lot? Does it matter? I figure if the screw is removed completely and I'm squeezing hoses, the bubbles may be pushed out when the coolant gushes out through that hole, but more air could be sucked back in when you let go of the hose and the coolant falls back into the line.

Also, what is the reason for turning on the heater? Just to open that part of the system so it's also circulating? Or is it to help keep the engine cool so I can let it sit longer idling. Basically, did I need the fan on in the cabin or not?

And one more thing: I'm still not clear on exactly how the coolant reservoir works. I thought it was connected to the top of the radiator via vacuum tubing, so it acts as an overflow, but also the radiator sucks in more coolant from the reservoir fairly quickly if the system is low...

Anyway...back to the most important thing. My shit is fixed! I'm so much happier now and I don't have to have my girlfriend drive me to work today! :)

Thanks for all your help and good information, guys. Here's a picture of my reservior for kicks (it had no cap when I bought the car). Yes, it's pretty and functional.

http://home.comcast.net/~fastexpand/reservoirmed.jpg

At hot time, don't open. Abunai Abunai Abunai!!

http://home.comcast.net/~fastexpand/bleedscrewmed.jpg

[tig_tech]

Well the purpose of the overflow tank is a place for coolant to run to when the boiling point of the coolant in your motor passes the radiator caps pressure limit. You gotta remember the radiator cap is also to increase the boiling point of the coolant in your engine. Its like a pressure release cap and functions similar to a pressure cooker and needs to relieve pressure of the system when the coolant heats up and expands. It also keeps air out. When the coolant cools back down, a vacuum is created that sucks the coolant from the resovoir tank back into the coolant system. Hope this helps out.:)

[granttttt]

As far as the bleeder screw goes, as long as it is opened enough for air to come out you are good. I personally like to completely take the bleeder screw off because I am scared that if I leave it on it might fall to the ground while the car is shaking. There is that washer on the bleeder screw that you don't want to lose.

[sillydrift]

you might want to check the water pump, my s14 was overheating and i saw no leaks then one day i let it run and it was leaking from under the water pump, i changed it out along with the thermostat and worked like new, be sure to air bleed the system like mentioned above (my water pump would not spin well either i found out and was all corroded and messed up inside

[tig_tech]

Yea alot of water pumps have holes located on the underside where it leaks from when they go bad.

[MELLO*SOS]

you might want to check the water pump...

He said he already got it fixed bud. Air in cooling system = overheat as I'm sure you've learned sometime in the past...

Rock on guys! I think I fixed it

Lurkable, it doesn't matter if you turn the fan on or not. The heater is turned on so the coolant can circulate through the heater core and pull out any air that may be trapped in the lines or core.

BTW you should steal an overflow cap from the junkyard, that tinfoil, ducttape and zip tie mess looks atrocious LOL.

[ericcastro]

and as for squeezing the line, correct.
thats where i meant to squeeze it, gets the couple last bubbles out that can hide in that hose since its the highest elevated part.