Auto Repair Help

by Mark Davidson

The engine overheats or boils over. The temperature gauge reads higher than normal or the instrument panel “hot” light is illuminated.

The most common cause of an engine overheating condition is a defective thermostat. However, there are numerous items that can cause an overheating condition. Coolant loss will also cause an overheating condition. If you are experiencing coolant loss in the form of a leak, refer to the “Coolant Loss” symptom on this site. If the vehicle overheats and has excessive white smoke from the tail pipe, refer to the “Excessive Smoke From Tail Pipe” symptom (also on this site).

You should start your diagnosis with a visual inspection of the cooling system. Ensure the coolant level is at the proper level. Do not remove the radiator cap when the engine is hot! Inspect for warped belts and leaking hoses. If the engine overheats a few minutes after start up, the most probable cause is a defective thermostat. If the engine overheats after several miles of driving or only overheats at low speeds, you should inspect the cooling fan operation and radiator. On vehicles that use an electric cooling system, ensure the cooling fan is coming on at when the engine reaches operating temperature, usually between 195F – 220F. Let the engine idle with all of the accessories in the off position (such as A/C). Monitor the engines temperature by observing the temperature gauge. The cooling fan should automatically come on prior to the gauge reading hot. If it does not, promptly shut the engine off. If the vehicle is equipped with air conditioning, turn it on and observe the cooling fan. If the fan comes on, the most likely cause is a cooling fan thermostatic switch. If the fan does not come on, further diagnosis of the fans electrical system will be necessary.

On vehicles with a conventional radiator fan, inspect the fan for damage. Ensure the fan clutch is operating properly. Have an assistant turn the engine off while observing the fan. The fan should only spin for about 2 seconds after the engine is shut off. If the fan continues to spin for several seconds after the engine is shut off and the engine only overheats at low vehicle and engine speeds, fan clutch replacement may be necessary. If the cooling fan operates properly, inspect the radiators external cooling fins for excessive debris, such as bugs and dirt. When the engine has cooled down, remove the radiator cap and inspect the inside of the radiator for excessive scaling. The tubes that run accross from one tank to the other should be clear of build up. If the radiator is not equipped with a conventional cap, it may be necessary to remove one of the radiator hoses to perform an internal inspection. You should do this when the engine is cold. If necessary, the radiator can be removed and inspected by a radiator shop that will provide advice. A radiator that is plugged may require a “Rod Out” to restore proper operation. If the radiator, cooling fan, coolant level and thermostat are in proper working order further diagnosis will be necessary. It is possible that the impeller on the water pump is damaged or the vehicle has a blown head gasket or cracked cylinder head. White smoke from the tail pipe is a key indicator of such a failure.

Use extreme caution when working on the cooling system. The cooling system is under pressure when hot and can cause extreme burns if opened when hot. Use caution when working around hot or rotating engine parts. On vehicles with electric cooling fans the cooling fan starts automatically. Keep your body away from the cooling fan at all times. Radiator flush agents may be an aid in removing scaling from the radiator. Use these products as per the manufacturers recommendations.

(Mark gave up on sports when the Browns left Cleveland and now spends his Sundays working under a shade tree in the back yard tuning his son’s soap box derby car.)

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52 Comments on "Diagnose Engine Overheating"

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3 years 6 months ago

engine still overheating after replacing heads,headgaskets thermostat and has a new raditor and cap’ only thing i having replaced is the water pump itself.please help me with this problem.

1 year 2 months ago

Check your oil levels. If oil type is right (10w30 or whatever your vehicle requires) then check all the hoses. If all the hoses are good (no bends, kinks, collapses) then double check your coolant levels and that correct coolant type and blend are in your vehicle. After this, make sure you installed the thermostat with the air valve in the up position (some thermostat do not have this, google for further explanation). After that assuming your head, gaskets, radiator and cap have all been replaced, check the belt (engine off of course) that runs your water pump; check if it is loose (should only give about 1/2 inch of play. Wether it’s loose or not, at this point you should probably replace your water pump and belt at the same time. I understand this is a lot of work, but I believe that’s the culprit. If you wanted to procrastinate this potentially incorrect diagnosis, you could flush your cooling system with a kit or a shop to make sure that won’t be an option in fixing your overheat condition. Otherwise just make sure you nail the timing from start to finish and if the timing is off once your finished, don’t run the car (if it will run at all) until the timing is corrected. Best of luck!

3 years 11 days ago

Hi William, Please try and check all the radiator hoses followed by the water pump

[…] I'd take a look at this: Diagnose Engine Overheating – Auto Repair Help If turning the heater on makes a noticeable difference, the radiator becomes a likely source of […]

Ahmed Soorma
2 years 6 months ago

I just had the radiator removed from vehicle and found that one of the ends at the radiator metal body had a small section (ribbed) was slightly loose.
Had the radiator body internally cleaned and then used solder mix with “Magic Epoxy” and spread it over the affected area.

Replacement cost of that end is the next solution if the radiator leaks again.

Have the radiator checked by a good workshop who will not chisel you off.

john sooner
2 years 4 months ago

My engine is overheating the thermometer does not go off scale but is high. The electric fan runs does mean the thermostat does not need changing. I note you recommend changing the thermostat as a first diagnostic action but is that even if the fan works, I do get Blue smoke but not exceessive

terry bell
2 years 1 month ago

I have a Pontiac astex it is over heating new water pump new radior new thermostat new radior cap there is no white smoke from tail pipe it dosnt use water no leakes can you tell me what is next?

terry bell
2 years 1 month ago

fans are also working

Josh Cataldo
1 year 3 months ago

I have a 2000 Cadillac Seville SLS 4.6L. The car has 175,000 miles on it.
The car over-heats while driving faster and cools when driving slower but still stays at the half-way point on the gauge. The thermostat, lower and upper radiator hoses have been replaced and the fan does turn on. The car still run dangerously hot. Any ideas?

Josh Cataldo
1 year 3 months ago

I did do the chemical block test. Both times the fluid chemical did not change color. The fluid chemical stayed blue.

1 year 3 months ago

my alarm says “engine hot turn off A/C and idle enigine”
I changed the thermotat no help. it has no signs of leaks
and as long as I am moving its fine but when i stop i have to turn the car off once i start moving temp goes down fast

Ken Barnes
11 months 6 hours ago

Check that the fan is turning

Lisa Neufeld
1 year 2 months ago

My car only heats up when it is idaling or when is at a stop. The temp goes back to normal when driving especially on the freeway. I’ve replaced radiator, water pump, timing belt, cooling sensor, and thermostat. I’ve actually replaced the thermostat several times. Once repairs had been done car would be normal temp for a bit then it starts to heat up bout 2 weeks later. There are no leaks and head gaskets are good. Any suggestions?

Lisa Neufeld
1 year 2 months ago

Also all fluids are good with no loss.

9 months 18 days ago

This is exactly happening to me. Did you ever find out what it was?

1 year 1 month ago

my car is over heating while i am corsa el 43 ( 5 e )

1 year 1 month ago

i have a 02 300m 3.5 eng g, i had the radiator replaced for a leak, after that it would overheat below 2700 rpm in any gear,above it cooled fine, had the w/p replaced & all timeing parts while they were there, still same promblem, installed another radiator,flushed cooling system, put in correct fluid twice, the initial rad had wrong fluid put in, changed thermostat, hollds 15 psi for 24hrs then released, original spark plugs good,still the same problem, any ideas, thanks pete

1 year 15 days ago

Where is the thermostat found on hino ho7d

suzette van tonder
1 year 2 days ago

We have a 2003 opel zafira 1.8. The car keeps on overheating if driving on open road. The waterpump,cambelt,thermostat, radiator are all replaced and it still overheats. What can this be.

[…] resulting in an imminent fire. To prevent the engine heat up, experts advise all drivers to closely inspect the engine temperature, especially in hot summers. If you notice temperature rising too high, stop your car by the road […]

11 months 13 days ago

Dear ,
i have a nissan pathfinder 2004 running 123000 km .once i drained the coolant and i refilled it the engine started over heated , after that i change the thermostat and i flushed the radiator .but still the engine became over heated , special when you gave more torque the temperature will be increase .
can you help me to find the failure .


3 months 12 days ago

You may have created an air pocket in engine and engine needs to be burped. This can be done by elevating from of car removing radiator cap and letting engine run until thermostat opens. Then refill radiator to make up for displaced air. I’ve had this happen before too

11 months 8 days ago

Jeep wrangler 2000, will only overheat after highway drive around 25 minutes. Local drives the needle sits just above halfway. I replaced the thermostat.

10 months 3 days ago

So my cluster is marking its over heating but my engine is cold and am on the road the engine is not overheating at all is it my sensor?

7 months 22 days ago

did you solve it. having a similar problem now

9 months 7 hours ago

Willim . Cheek the water jacket hols he is open ?

9 months 7 hours ago

Willim . Cheek the water jacket hols their is open ?

8 months 16 days ago

yes i have a question my car overheated and i took it to a mechanic he said the the muffler is licking water and there is some white smoke coming out he said that the best thing is to change the motor what do you think i should do another person told me i could fix just half of the motor that will be doing the job but i do not know to much of cars and i do need that help

6 months 6 days ago

I have a problem with diesel engine. After rebuild (new piston rings bearings and gaskets) it wont start. Timing belt ok. It is posible to start it by pushing the car and then engine has no power, can’t work on idlle and over heating very fast (I remove thermostat). Also I check bearings and it looks good. Engine is not hard to move with key on crankshaft. All liquids ok. Help please.

Eng francis okpu pope
4 months 7 days ago

Recheck the timing & change moving disk or plate

5 months 29 days ago

I have 2002 chrysler sebring. Temperature gauge say normal but the car is overheating.

4 months 24 days ago

my car is overheat while driving and the speed is very low while pushing to drive. Could you help me with it??

4 months 24 days ago

the model is Nissan, Liberty

I really need to know the spare parts and also to be fixed if you know.

Cate ndish
4 months 7 days ago

My car is overheating,did ovahaul but stil overheating with alot of smoke.please help urgently.

2 months 16 days ago

sure head gasket problem

4 months 3 days ago

I have a 04 Ford Focus. In the last few weeks I noticed my temp gauge started moving up. It hasn’t reached red yet but it stops right before. At first it was only happening if I drive in hot temps/long distances and especially and stopped at lights. But now it’s been happening in cool temps without much driving. Coolant level good. I have been told I have a coolant leak but it hasn’t been a problem till now.


3 months 8 days ago

My boyfriend just put in a new thermostat, new top radiator hose and a new radiator my car is still over heating can somebody please give me a helping hand here and let me know what’s going on with my car I do not know nothing about cars

Tommy Rancher, sr
3 months 4 days ago

I have a 2003 Durango, it keeps shutting down when the guage reach the half way point. I change the radiator, starter, alternator, and thermostat. But it still shut down when it reach the half way point. Please help, I have spent over $500 in one week on this truck..

2 months 29 days ago

i have replaced gasket, radiator cap, water pump, and the sensor, and crankshaft sensor, cleaned my radiator but the vehicle is still overheating what might be now the problem please assist

2 months 27 days ago

My son has a 2002 Honda Civic with 70,000 miles. It broke down, it was overheating. We just got the radiator and thermostat changed. The temperature gauge is still going up but car doesn’t show signs of overheating. Running smooth. Any idea what else might be happening?

2 months 24 days ago

Hi my gmc envoy keeps turning off and the computer reading said faulty thermostat. Is it possible for that to be the cause even if the vehicle is not overheating?

2 months 16 days ago

last month i bought audi tt 2003 93000kms,it’s temperture gauge shows 90 whenever we starts the engine and after drive 5min, it goes 130 really fast ,but i checked radiator( water and coolent mix was just normal hot) ,we changed temperture sensor aswell but still same problem.please help

2 months 7 days ago

my problem started one month ago when i bought gmc acadia slt 2011. there was a problem in the differential and i solved by replacing it . i drove the car for five days and everything was fine. then the engine started overheating two lines after the middle. which means the first quarter. i took my car to the mechanic and he changed the thermostat , the fans and the sensor and some fuses , i took the car and after two days it started overheating and the ac started turning off. i took to another technician and he did know what to do . in liberty which is the car company said it is fine but actually it was not fine . one mechanic told me to check the condenser and i did and it was clogged and leaking and I changed it. then the car started reducing the engine power and makes white smoke with a fuel smell . i took to the company again and they changed the injectors and high pressure pump and some other stuff . i took the car and the ac was not working fine. and the car overheated again. i took to another mechanic and he changed the ac compressor and valves the front and rear and condenser again.I took the car home . it did not over heat. the second day it overheated . the car overheats in traffic and if turn the ac off it becomes fine . the engine is good and the power is fine . all the mechanics said there is no faults in the engine. I am still suffering , can you help.

1 month 26 days ago

I have a 04 Jeep Grand Cherokee Largo. I just replaced the cooling fan and it still overheats. What else could it be.

shawn michael
1 month 24 days ago

check for a fuse, i replaced my fan and let it idle so that i could see if it would over heat, it took 30 minutes? and it overheated, this told me there was another problem, i checked for the fuse and sure enough it was a fuse that was blown. now you would say, should have checked the fuse first, yes, but there was a reason why the fuse blew, and so by changing the radiator fan helped because it never occurred again.
so there are a few things to watch for
radiator, (leak) (low level)
rad fan
fuse relay
also, when in trouble and see the temp gauge hitting hot, turn off ac turn on heat and hit the fan to blow as much of that heat out of the engine into the car, open the windows. also, if you can, get your speed up and put into neutral and turn engine off and coast as far as you can before turning on engine again, and do it again, this will help cool the engine down so that you can get back, depending on how far.
a rad flush should be performed at times also. as per maintenance instructions.

1 month 21 days ago

i have a 2008 pontiac g6 gt 3.5L. i have checked all major problems for why my car is overheating. I’ve checked thremostat, water pump, there are no leaks on the hoses. coolint is full. kinda stuck on this one. any ideas on what my problem could be? i would be very grateful if someone could help me with my problem.

1 month 18 days ago

I have a 2005 Kia Sedona. Our van overheats after a few miles. It has no heat when the car is first turned on. After about 10 mins the heat will kick on and the gauge will go back to normal range… then it will start to overheat again and then heat will start back up and it will go back to normal range. Can you please help us figure out what could be the problem. We do have to add coolant to it also, but there doesn’t appear to be any leaks (or at least nothing we can see under the van). It doesn’t hiss when it overheats and no smoke from the engine.

1 month 10 days ago

how long does it take a large V8 engine to cool down after being shut off and parked in a one car garage in Florida

1 month 8 days ago

my engine is over heating..i replaced thermostat radiator cap fluids and passes the midway mark of the temperature gauge bout 3/4 of the way then cools back down a little then sits there havent had it hit the red mark..but i need to fix so i can drive with no worries..any help to solve this problem?

1 month 8 days ago

MY car was being driven by friend in a hilly area, he reported that at end it got over heated and there was some gas coming out of radiator bottle, after it cooled down approx 1.6 liter water was required to fill radiator and extra bottle.
After that car is normal i did nt experienced any change except some smell from bonnet, should i go for any inspection/maintinance?

1 month 3 days ago

Hi i have a Hino 500 1626 truck that overheats and cuts off while your driving what can be the cause of it, but when you try to start it – it starts with no problem.

Tabitha Patterson
7 days 5 hours ago

My car gets hot when u first drive it and then if u pull over and open the radiator cap it goes back down …. There is no water in my oil ppl keep telling me it might be a cracked head gasket but I’m wondering if I should replace the radiator ? Help me please