Thermostat....right?

[C91BLX7]

So yesterday night being one of the first cold nights this year, i noticed after about 20 minutes of highway driving the temp needle was still all the way down.
If i stopped at a light I could watch the temp rise up to the normal spot. Start driving again and watch it go down.

Also the heat wasn't anywhere as hot as it should be.

So I believe the thermostat is stuck open, or not closing enough? Does that sound right?

[EJX_Michael]

Do the hose test... From ice cold, let it idle and feel the hoses.

The top hose should get hot, but the bottom will stay ice cold until your thermostat opens which should take a good 7-15 min.

So if they both get warm in the first few min, its stuck open.

[9tAkord]

So yesterday night being one of the first cold nights this year, i noticed after about 20 minutes of highway driving the temp needle was still all the way down.
If i stopped at a light I could watch the temp rise up to the normal spot. Start driving again and watch it go down.

Also the heat wasn't anywhere as hot as it should be.

So I believe the thermostat is stuck open, or not closing enough? Does that sound right?

I think your thermostst is broken and it is stuck in the "open" position. Good thing with it is that you are not overheating, although you still need to change your thermostat...

[batever]

My understanding is that the temp gauge gets its reading from the temperature sending unit, not the thermostat. Your thermostat and entire cooling system could be fine and if the TSU is bad, any the gauge will read wrong.

It sounds like you may have air in your system though (an air pocket around the TSU will cause it to read low, then when coolant sloshes on it it will heat up and the gauge will increase.

First bleed the system. put the heater temp. to high (to open the heater core) and open the radiator cap. Make sure both the radiator and the overfill container are up to the top and to the full line, respectively.

Open the bleed valve near the thermostat on the upper hose.

Now start the car. watch the bleed valve and close it when a clear stream of coolant comes out. Top off the radiator now.

With air out of the system the TSU should be able to give a good reading, as reflected on the gauge cluster.

Now make sure the cooling system is basically working:

The first thing to do would be to make sure that the thermostat itself is working correctly, because if it is the cooling system at least is working.

put a meat thermometer or instant read therm. in the radiator, then start the car. Watch the temperature on the thermometer. It should rise slowly, then when the the coolant at the thermostat melts the wax pellet in it (around 180F) hot coolant will flow to the radiator and you will see a faster temperature rise to 185-195F. The fan will come on, too. At this point your gauge cluster should also indicate normal operating temperature, the needle slightly above the halfway mark. If the TSU is bad or there is air around it, it will still read low.

If the thermostat doesn't open within like 7 or 8 minutes of starting (the engine feels hot already and the fan doesn't come on,) stop the car because you don't want the engine to overheat. In that case you may also have a bad thermostat.


If this bleeding procedure and test shows that the cooling system is working correctly, and the temp. gauge is still reading low, I would say you have a bad TSU. However, I suspect you just have air in your system, probably from a leak in one of your hoses or in one of the clamps or joins.

good luck

[batever]

i reread your post and after that i agree that yes, it could be the thermostat being stuck open, as opposed to there being air in the sytem, makes sense. The gradual rise on the temperature guage when the car is stationary yet running would be consistent with that. The "hose test" suggested by EJX Michael is a quick and dirty way to check it, definitely.

The thermometer test will show that too. YOu will see a fairly constant rise in coolant temperature in that case, with no "spike" in temperature because no coolant is being held back from the radiator at any point.]

Also the fan may come on almost immediately on starting, rather than waiting until the coolant gets to a certain temperature. I am not clear on whether the fan runs off the thermostat or the TSU, though I believe it runs off the thermostat.

[MikeW]

^^^Wow!

I kinda have the opposite problem. Mine goes to, and sits in, the middle and when i stop, it goes up. Heat makes it go faster, AC keeps it down.

I'll have to try this bledding technique.

Drew GL with it, whatever it is.

[batever]

^^^Wow!

I kinda have the opposite problem. Mine goes to, and sits in, the middle and when i stop, it goes up. Heat makes it go faster, AC keeps it down.

I'll have to try this bledding technique.

Drew GL with it, whatever it is.

While it's never a bad idea to make sure there's no air in your cooling system, I don't think you have a problem by what you said, unless that needle is going WAY up on when you are at a standstill.

It is normal for the coolant temperature to rise somewhat when you are at a standstill, because there is no wind blowing up against the radiator. If it goes up a lot though that could be a problem. In that case you might have a faulty fan (fan is supposed to help cool the radiator, particularly at vehicle standstill when there is no rush of air from the front of the vehicle)

Before jumping to conclusions I would do the thermometer test with your car and note what temperature the coolant gets to and check it against spec. I'm not sure, but I don't think it should get higher than about 200-205 F. You should double check that figure though.

Also, make sure your coolant mixture is correct, as if you get too far below 50/50 coolant mixture it can affect the anticorrosion ability and overboiling protection of the coolant, and if it gets above 60/40 it can decrease the heat carrying capacity of the coolant mixture I believe. You can get an inexpensive tester that measures your coolant vs h2o percentage, it's like a little thermometer looking thing.

[C91BLX7]

Good shit batever

Anybody know off hand how much a OEM Honda themo would be?

[MikeW]

I use the 50/50 mix so...

The needle never "shoots" up, but it does goes up to about 3/4+. And like i said, it only does it when i have the heat on. Take me about 15mins to get to work, and its usually doing it about the time i get to work.

It also doesnt usually do it on the highway. Id be worried if it did, cuz i know thats really bad.

Anyway, sorry for the jack Drew. Least im on-topic.

[C91BLX7]

I use the 50/50 mix so...

The needle never "shoots" up, but it does goes up to about 3/4+. And like i said, it only does it when i have the heat on. Take me about 15mins to get to work, and its usually doing it about the time i get to work.

It also doesnt usually do it on the highway. Id be worried if it did, cuz i know thats really bad.

Anyway, sorry for the jack Drew. Least im on-topic.

No problem

Do your fans kick on? could be the thermo not opening enough? waterpump good?

[MikeW]

WP's good. Fans come on.

Dont notice if they come on while im driving, but they come on after ive turned it off.

[batever]

I use the 50/50 mix so...

The needle never "shoots" up, but it does goes up to about 3/4+. And like i said, it only does it when i have the heat on. Take me about 15mins to get to work, and its usually doing it about the time i get to work.

It also doesnt usually do it on the highway. Id be worried if it did, cuz i know thats really bad.

Anyway, sorry for the jack Drew. Least im on-topic.

Sounds like your system is fine, I wouldn't mess with it. Needle 3/4 up sounds about right. It couldn't be a bad idea to throw a thermometer in your radiator though if you are concerned at all, and see how the temp. actually reads there. Are you sure it only does it with the heat on? it should be the reverse: AC dumps heat INTO the cooling system, while the heater fan bleeds heat FROM the cooling system. So that part is a little baffling to me: the heater fan should tend to cool the system down by transferring heat from the coolant into the air in the cabin, causing a relatively lower temperature reading.

The temperature needle doesn't go up as high on the highway because of all the air blowing against the radiator and cooling it down. The radiator fan is to kind of provide the same blowing/cooling effect when the car isn't moving fast. They also will run after the car is stopped, until the coolant temperature is low enough then they will stop.

[MikeW]

Yeah, now thats it gotten colder, i have the heat on, and the temp needle is usally up to 3/4 when im at the light by work.

Before, when i had the AC on, on the way home, the needle would never go above half.

[batever]

Good shit batever

Anybody know off hand how much a OEM Honda themo would be?

Thanks, C91BLX7!

I have no idea how much the therm. costs. I know it's not "expensive". but nothing beyond that.

[C91BLX7]

Thanks, C91BLX7!

I have no idea how much the therm. costs. I know it's not "expensive". but nothing beyond that.

http://www.hondaautomotiveparts.com/...ry5=WATER+PUMP

Thats not bad, but I hope the dealer doesn't jack up the price.