thunderfck23

Hey guys - newbie here

I have a '97 Civic Ex and for the past year or so my car has been overheating when I'm at a stop, specifically when I have the AC on. Since then I've replaced the fan sensor which fixed the fan, flushed the radiator, had tune ups done and made sure all hoses are on correctly. None of this has worked.

Every 2 days I have to replace the coolant because there's no more in the overflow tank.. and then it overheats again. From what I've seen, there's no coolant on the ground after driving so it's probably not a hose.

Anyways, a mechanic 2 years ago said I had a cracked manifold. Could this be causing my car to overheat? I smell a burning smell every time I get out of the car. Could the coolant be evaporating on the engine?

I don't really know much about cars so thanks for any help.

thunderfck23

Also, I had my thermostat replaced 2 years ago

zXeX

There's a freeze plug on the back of the block on the drivers side, it could be leaking there when the engine is under pressure. Look back behind the alternator or under the car along the bottom of the block/above the oil pan to see if you can see any traces of coolant seeping down. You could possibly be leaking around the water pump, water bypass/crossover hoses or perhaps even a leak around the coolant port on the head gasket which would blow the coolant out the exhaust (worst case scenario). All the others could result in a subtle loss of coolant without leaving a puddle, it just seeps out under pressure as you're going along and burns off on the hot engine. Check along the radiator itself as well, a worn rail could be leaking as you go along.

arizaga8799

the easiest way to figure this stuff out is start small and work your way up. head gasket should be the last thing to worry about, altho they seem to be pretty common on these cars. i have a feeing its due to people inadvertently (or on purpose, thanks honda owners manual) driving their car in winter til the temp gauge reads in the middle/normal, then cranking the temp dial from cold to hot. on this particular gen, this opens a large heater hose valve and allows ice cold coolant sitting in the heater core and dash hoses to go straight into the hot engine head. as you can guess, this is really bad for the engine. instead, leave the temp dial on hot for the whole winter and just turn the fan to OFF before the car warms up. this allows the car to still warm up fairly quickly, and you will have all the coolant circulating already when the car is warmed up. then adjust the fan speed to your liking or leave it off and air will blow in when driving on its own. on the freeway, i doubt you even need the blower fan at all.

anyway, ordered list of overheating checks:

1. thermostat. drive the car til its fully warmed up, at least 30mins. open hood and feel top and bottom radiator hoses (the big ones). top should be hot, bottom should be hot. this means coolant is going to the radiator and everything is normal. if bottom hose is cool or warm, thermostat is either stuck closed or not opening enough. can cause overheating under certain conditions. solution: replace with oem honda thermostat.

2. fan motor, fan relay, fan fuse, or fan temp sensor. something is causing the cooling fans to not come on like they should when the car is at idle for extended periods of time in hot weather. turn the a/c on and see if both fans come on immediately. if so, motor/fuse/relay is fine. fan temp sensor in the coolant passage could be bad. on a hot summer day, outside temp of 90F or higher, drive the car til it warms up fully. park car and leave it running. within 5 mins the fans should turn on. if not, bad fan temp sensor. replace it and retest. a fan problem can cause overheating at idle in stop and go traffic, but not while the car is driving above 35mph (then the radiator will be doing its job).

3. air bubbles. can cause real or fake overheating. air in the cooling system is usually caused by doing a coolant drain and fill on these cars, since the radiator passages are so tiny compared to cars with larger engines. air bubbles around the cooling passages can cause hotspots to develop, which can cause serious problems with the engine. air does not cool anywhere near as good as liquid. air can also confuse the engine coolant temp (ECT) sensor and cause it to read a higher than normal temp. the sensor must be inside the coolant to work properly. to limit air bubble formation when doing a coolant change, you can turn the temp dial to full COLD before shutting off the car. you can also choose not to open the engine block drain bolt. note that doing these things will allow some old coolant to stay in the system. so you may want to do a second drain and fill later on once the new and old coolant mixes. after coolant change, make sure you bleed the majority of air out by following this procedure. drive car til fully warmed up. park on a sharp upward incline or jack up front of car. carefully remove radiator cap using a lot of shop towels to catch the coolant spray. leave cap off, start car, turn temp dial to max HOT. turn fan on one notch. feel the air coming out. if cool, you have a long way to go. watch the radiator and add coolant so that you can see the level near the top. keep watching for air bubbles for at least 30 mins, or until no large bubbles are coming to the surface. you can tap or squeeze the large radiator hoses and rev the engine to 3k rpms occasionally to speed up the process. when bubble formation has stopped, put cap back on and turn off car. go for a drive and turn the fan on. hot burning air should be coming from the vents. some water bubbling noises may be heard in the dash for up to a year afterwards, but these small bubbles will eventually come out. make sure the temp gauge does not go above normal.

4. radiator cap. a faulty cap that does not pop open and allow coolant into the overflow tank can cause cooling system pressure to rise above normal. this can lead to hoses failing, water pump leaking, and a variety of other problems that can make it seem like a headgasket leak. replace cap with a new honda oem part every 5 yrs to prevent any problems.

5. ECT sensor. already mentioned, this sensor is extremely important. not only does it tell you how hot the coolant is (via the temp gauge), it also tells the ecu so it can adjust how the car runs. usually you will get a check engine light for a bad sensor, but not always. replace this if you seem to be overheating for no real reason, and the engine bay does not seem to be hotter than normal and the coolant level is normal.

6. clogged radiator, cooling system, or other. if you have an older car where the coolant was never changed, chances are you have junk inside that could be clogging parts of the cooling system. you can check for radiator clogs by warming up the car, then using an IR thermometer to check the temp of various areas of the radiator. if one or more spots are very cool, you may have a blockage. if you drain the coolant and find any sort of debris, try a power flush of the system and hope that most of the chunks work their way out. it can be a huge challenge to clean up a cooling system like this because there are so many small passages where clogs can occur.

7. physical coolant leaks. if you are losing coolant and there are visible leaks, trace where they are coming from and fix the leak (hose, water pump, engine block, etc). failure to fix leaks can result in overheating when enough coolant is lost. if the overflow tank becomes empty, the cooling system can suck in air and make the situation even worse.

8. head gasket. you finally arrived. it wasnt easy, but now you are almost sure the overheating is caused by a gasket leak between the engine head and block. how can you make sure? lots of ways. a large leak can easily be detected by checking the compression of each cylinder. the stock rating is roughly 128 psi, but you are looking more for one or two cylinders that are very low compared to the rest. with a small gasket leak, compression can come back normal on all cylinders. if the oil looks milky, and the coolant looks oily, more than likely the two are mixing together. if you have a misfire when cold starting the car (whole car is shaking violently for a minute), that can be an indication of a slow leak where coolant is filling one or more cylinders. when the car warms up, the coolant burns away and car runs fine. you can have the cooling system pressure checked as well. lower pressure can mean a physical leak or also a gasket leak. pull all the spark plugs and look for white deposits that can indicate burnt coolant.do a gas test of the coolant that can indicate the presence of hydrocarbons leaking in from combustion. be complete and do as many tests as you can. a blown headgasket, if small, can be driven on for a while. but it will get worse and can eventually cause serious damage, even if you are not overheating right now. usually coolant that disappears from the reservoir with no reason always points to it being burned in the engine from a headgasket leak.

arizaga8799

could a bad oil pressure switch cause random overheatings?it seems to only overheat when I go up a hill or countinously run high rpms.

arizaga8799

is their anyway of checking to see if the cap is bad?