car overheats, heater is cold... thermostat?
 

Hey recently my car has been overheating. When it's overheating, the heater blows cold air. The heater works perfectly, it's hot and nothing appears to be wrong. As soon as the temp starts rising above normal, the heater starts blowing cold air. By cold I mean the same temp as outside air, unheated.

Does this mean my thermostat is bad? The car runs fine without overheating most of the time, but sometimes it overheats. I'm trying to track down the source of the problem.

Help, thanks for replies!

Re: car overheats, heater is cold... thermostat?
 

had the same shit last month it was my water pump do ur thermostat and if it wasnt that ull have a new thermostat and u wont have to worry about it then u can check ur water pump

Re: car overheats, heater is cold... thermostat?
 

I will replace the thermostat tomorrow. I won't do the waterpump until I hear more experienced peeps comment on this. If the waterpump was dead, the car would overheat constantly, as far as my understanding.

Re: car overheats, heater is cold... thermostat?
 

Sorry to thread jack, but does anyone know why you ccant use a stock thermostat on a kswapped car? Y do you have to use a different one?

Re: car overheats, heater is cold... thermostat?
 

sounds to me like the thermostat. my water pump went bad last year. just started leaking underneath it out of the weephole. you losing coolant? either way the thermostat is where i would start. water pump was a pretty good job to change. my crank pulley bolt was insane to remove.

Re: car overheats, heater is cold... thermostat?
 

My thermostat failed recently (to open) and the heater blew hot air.

I would suspect the valve for the heater or some kind of blockage in the heatercore or heater hoses. As far as the overheating it could be the thermostat, waterpump, leak/low coolant, fan not coming on or clogged radiator.

Thermostat, waterpump or coolant low should cause the car to overheat right away once it warms up.

Fan not coming on will overheat when car is driving slowly/sitting (no air blowing through the radiator)

Clogged radiator will slowly heat up more and more as you drive at higher speeds/rpm/engine load.

BTW - when I noticed my temp at 7/8 I turned the heater on and the temp gauge went down to normal. I suspect this did not keep the engine temp at normal because the head gasket still gave way (205K miles). According to the gauge the temp never went into the red. I am now in the process of replacing the engine with a remanufactured.

That's my Capt. Obvious report for the day.

Re: car overheats, heater is cold... thermostat?
 

r u leaking from anywere

Re: car overheats, heater is cold... thermostat?
 

it could be the thermostat or that you are low on coolant. It probably is not the water pump because the car would overheat constantly if it was.

Re: car overheats, heater is cold... thermostat?
 

I will replace the thermostat when I next get to a parts store.

This reminds me - after changing the clutch/flywheel I now notice a coolant leak. It's weird because it doesn't seem to be actually leaking coolant, just blowing air and making a sizzling sound. Maybe I'm losing coolant in the form of steam...

It's right where the top radiator hose connects to the motor, near the little air-bleeder valve. It's not the bleeder, that's tight. It seems to be coming out between the hose and where the hose connects to by the clamp. I don't think the hose is bad, maybe I cracked something on the metal flange the hose goes to when I was breaking nuts loose on the clutch/flywheel job. I was thinking originally that I accidentally dropped metal shavings or some chunk of garbage into the thermostat hole and that was funking it up.

Hopefully I didn't crack the flange. Hopefully it's just corrosion on the outside of the flange that needs to be sanded off preventing a good seal to the hose/hose-clamp.

any ideas? thanks much for the posts!

Re: car overheats, heater is cold... thermostat?
 

it makes sense now... little sizzling noise is coolant escaping in the form of steam, which means less coolant, air in cooling system, cooling system not cooling properly, overheating. The heater not working makes sense too... there's air blowing through the heater core, so obviously it's not going to get hot. There must be hot liquid (not air) in the heater core for it to work.

Now I just have to find the source of the leak....

Btw I never notice my fan going on. This obviously adds to the problem... Why wouldn't the fan be working? It's plugged in, so what could it be? The radiator is only a few months old btw, brand new and I just flushed it last week. I even used distilled water instead of tap water.

Helps Meeeezzzz! thanks much fo the wordz

Re: car overheats, heater is cold... thermostat?
 

I had a problem like that on an Integra a few years ago.....it ended up being the rad!

The radiator did work, but only partially, it had so much built up calcium deposits throughout it, it had a very low flow rate!! Replaced, problem fixed :)

Re: car overheats, heater is cold... thermostat?
 

you can jump the Fan so that its on as soon as you turn on the ignition. Thats what i did.

Re: car overheats, heater is cold... thermostat?
 

that sounds smart, even smarter than getting a different fan switch so it comes on at a lower temperature. I will do this as soon as I research it and find out how. Another thing I did already was use washers to space up the back of my hood 1/2inch so there's a bigger gap for air to circulate through the engine bay. Looks ghetto as, but beauty, function, or practicality - choose two.

can't I also get a lower temp thermostat so it opens at lower temp? Or can I just take it out so it circulates coolant at all times? are there any downsides to this?

Re: car overheats, heater is cold... thermostat?
 

coudl be early signs of a blow head gasket check you coolanr level and keep an eye on it may be a pocket of air deveoping in the heater core.

Re: car overheats, heater is cold... thermostat?
 

A non-opening thermostat would not cause the heater to blow cold air.

Re: car overheats, heater is cold... thermostat?
 

The heater is behind the thermostat so as long as there is coolant, the pump is pumping and nothing is blocked you will get heat with a closed thermostat. I had a K car back in the day which had this problem and it was due to a bad head gasket. If there was a coolant leak somewhere it could cause the same issues as a faulty head gasket.

Re: car overheats, heater is cold... thermostat?
 

How did you do it? Remove the Crank pulley bolt I mean.
I'm working on replacing the water pump right now, and i don't know how to get it off without it spinning all over the place.
Any tips? Warnings?? Thanks!
-Mark

Re: car overheats, heater is cold... thermostat?
 

I've used an impact gun. It has always come off pretty easily but I have heard horror stories. Also once the bolt is off you need to use some kind of puller to get it off as I recall. It's been almost a year since I did it last. As I recall there is a rubber bushing in the pulley so you can't use heat or brace against the pulley itself. In the guides there is a description of it being done. The fellow there just took the cover off of the flywheel and had someone hold a flat head in between the teeth to keep the crank from moving while he got on the bolt with a breaker bar. Impact gun is the way to go though IMO if you have one / can get your hands on one.
An other bit of advice: when putting the belt back on it is easy to skip a tooth while tensioning. Get a paint pen or something to mark the belt and cam pulley so you know right away if you lost timing. The first time I changed the timing belt I did just that and didn't find out until I had it all back together and tried to drive away. The I had to essentially do the entire process over again. = sucks pain in the ass. It's an awful job on a Civic because there is essentially no room between the area you are working on and the wheel well. I think I might be loosing my rear main seal so the next time I do it I'm just going to pull the engine out.

Re: car overheats, heater is cold... thermostat?
 

SNap on sell a toll for it. Or get it from the dealer its called a harmonic balencer holder. It comes in handy. Or impact gun. You can use a torch. But you need to keep it on the bolt itself. of course everything it touches will get hot. But if you cant get off any other way its the last resort. It does suck though. If honda engines spun the way most engines did it would be as simple as putting a breaker bar on it and spinning the engine but... good luck

Re: car overheats, heater is cold... thermostat?
 

Why dont you do a coolant pressure test to see if anything is leaking. if its not leaking then when the car gets hot feelthe hoses if all the coolant hoses get hot its not the thermostat. if one of the heater core hoses isnt getting hot than your heater core is clogged. pull your plugs see what they look like. do a compression test. take the radiator cap off and see if the coolant level drops when you hit the throttle.

Re: car overheats, heater is cold... thermostat?
 

Thermostat may not be sealed right in the housing, had that problem just last week so I replaced the thermostat and seal while i had it apart just because lol, fixed all these problems. Idle surge at all?

Re: car overheats, heater is cold... thermostat?
 

bad head gasket

Re: car overheats, heater is cold... thermostat?
 

sounds like a bad head gasket to me.

Re: car overheats, heater is cold... thermostat?
 

Fix the leak first. take off the hose, clean teh spout and the inside of the hose from deposits, put the hose back on and clamp it tight. Then bleed the system properly.

Do not jumper the fan to the ignition. Do not install a lower temp, thermostat. At least if you want to do it properly. But don't install a lower temp. thermostat. Seriously, I graduated a 2-year auto course, am ASE certified, and work at a dealership. Don't do it. . . lol. An engine is designed to work at a certain temp, that's where it's most efficient.

Re: car overheats, heater is cold... thermostat?
 

and did you reverse flush the cooling system with water? make sure you do that to clean out all the crap from your engine passageways :)