Cold heater heater wasnt really warm last nite today heater is blowing cold engine temp is ok fans coming on but expansion tank is bubbling when u rev engine bubbling gets worse i think thermostat any advice would be appretiated

Low coolant, if there is an air pocket in the engine it will make it to the heater core. Once there , the air coming out is cold/cool. Once the coolant fills the heater core, it gets hot. If the coolant is fine hot or cold, then have the HVAC system scanned.

i had something similar once, it ended up being the intake radiator hose, it has a metal coil inside, mine was broken and when you revved the motor it would **** the hose shut and overheat, but under 2000 rpm it was fine .

when car is at operating temp both heater pipes should be more or less the same temperature. If one is cold, try getting the car up in the air so the radiator or expansion tank is higher than the heater...release (carefully) the pressure cap and give the engine three good revs, see if any air comes out and heater pipes equalise. I there is no air in your system you may have a heater water valve fault. Try to locate valve and see what contols it (mechanical , electrical, vacuum)..maybe itcan be manually moved to open, maybe it neds to be replaced.
If you replace it, the air must be bled from the cooling system (see above), but run car until warm with cap off and air will bubble out.
always check coolant levels later when car is cold. Top up coolant as required.

First check if you have any leaks in the cooling system , then check if level is correct(radiator and expansion tank , check level when car is cold , never open radiator when it's hot).
Then verify operation of radiator fan , if it's electrical fan it should comes on when temp. goes over normal,
if it's a clutch fan- it should pick up a speed and be more loud. If fan is not on and engine is starting overheating , check upper and lower radiator hoses.
If upper hose hot and lower hose cold or warm then you might have stuck close or prtially closed thermostat , difference between lower and upper hoses when t/stat works ok is about 10-15 degrees,
not really noticeable for hand.So if you don't feel a lot of difference between hoses temp. , and fan is not on , check fan or fan clutch itself.
If lower hose cold , replace thermostat and purge system.
If everything above is working properly , and it's still overheating , you may have bad water pump or head gasket.

After warmup it still blows cold, or only when cold? Normally the fan will operate independently of engine temp except in some climate controlled vehicles. As long as it blows warm air after engine is at temp that's a good thing. the heater uses hot water from the engine. Obviously the heater can't be warm before the engine is. If it's cold after the engine is hot, there are vacuum controlled "motors" on top of the heater box under the dash that move doors that control heat. Either one of the control motors or one of the doors have stuck or failed. Many also have a control valve on one of the heater hoses under the hood as well. If the engine comes up to temp then the thermostat is good (should be at about 210f) Only remaining item is the core itself which may be internally or externally obstructed.
All this being said, if it's good when the engine is up to temp, leave it alone...it's fine.

dear friend-there is a couple of things you can do to find the problem,when the engine is cold remove the radiator cap start the engine then look inside to see if the water is circulating,all so look for bubbles in the water,if there is bubbles,you might have a blown head gasket,if there is circulation the water pump is ok,then get the engine up to working temp,then feel both the top and bottom radiator they should be the same temp,if not then the termostat is at fault

Let your engine warm up with the rad. cap off and see if the coolant level drops. and make sure your overflow is full. It blows cold air because there is no water getting to the heater core. And it shows a normal(ish) temp because the water needs to be touching the temp. sensor. I really do think there is air in the system and there is not enough coolant but hard to tell from here. Also as with overheating any time make sure to check your oil and look for any coolant as the head gasket seldomly holds together if the motor overheats.

Is your temperature gauge working now? That is of more concern then your heater as you wouldnt know if your engine was overheating until its too late. Your heater core could be clogged, they get clogged quite easily. You can flush them or replace. The part is inexpensive but on some models you have to take out dash to replace them, but on other models it only takes about 30 mins and a few bolts.

dear sir,

the solution to your problem is simple. yes you say that it has a new water pump, but the reason that a vehicle bubbles out of the expansion tank is because the water pump is not circulating coolant, the coolant boils in the engine and bubbles out of the expansion tank. secondly the reason the fan never kicks in is because the temp sensor is not seeing the heated coolant because the water pump is not circulating the coolant through the cooling system. 3rd. the heater never gets hot because the water pump is not circulating coolant through the heater core in order for it to get hot and provide heat. and the temperature gauge never seems to go up because yup you guessed it, the water pump isnt circulating coolant in order for the engine temperature sensor to see hot coolant and thus send a signal to the engine temperature gauge as to the coolant temperature. i know you said it has a new water pump, but i have heard that this type of vehicle may come with a plastic fin pump. i would remove the pump and check the passages for foreign matter{ trash} in the passages as well as the condition of the new pump. also one last thing, the reason the vehicle died on the road in the first place was probably because it overheated. happy hunting and please post to see what you found. i am a mechanic by proffession.

sonds like air in your pipes!!! run ya engine with the lid off your expansion tank and put your heater on low until water starts bubbling and may start going down in your expansion tank and if so keep topn up to max mark!!!