Temperature gauge acting strangely

[Kassie]

 

My dash board temperature gauge will spike suddenly while driving. Sometimes it falls back to normal before I even get a chance to pull over. Other time it will fall after I turn heater on. It doesn't do this all the time. Sometimes it can be a week before it does it again. There is no rhyme or reason to it. My car is a 2000 Subaru legacy sedan. Here is what I've done so far....new radiator cap, complete radiator flush/refill, changed thermostat (twice), "burped" radiator, new coolant temperature sensor. I don't know what else to try. Oil looks fine, heater works great. HELP!!

[Kassie]

It's also has an automatic transmission, 2.5 engine

[Rooster2]

Did you replace the thermostat with a genuine Subaru OEM model, or top of the line after market thermostat? If not, it is the "cheapie" low budget after market thermostats that cause problems like you are describing. The cheapies don't open and close properly, and can cause over heating.

[Kassie]

The first one that I put in was cheapie. The second one(the one installed now) is the best aftermarket my parts store had(around $30)

[Rooster2]

The first one that I put in was cheapie. The second one(the one installed now) is the best aftermarket my parts store had(around $30)

You should be ok with the $30 aftermarket unit. That is what I spent for an aftermarket for my 99 OBW. Do you remember if the 2nd unit had more spring winding coils then the cheapie?? The minimal coils on the cheapie indicate that it is a poorly made unit. The better units have more coils, and therefore there is more coil to insert into the block upon installation. More coils do a much better job controlling the thermostat's action.

 

Next time, when you see that the motor is beginning to over heat, stop driving.... open the hood and look at the radiator over flow reservoir that sits on the side of the radiator. With the engine running, do you see bubbles rising to the surface of the coolant in the overflow tank?? If so, then that indicates a head gasket problem. Older Subie motors did that...........However, since your engine is I think you might have the 2.5, single over head cam. Head gasket problems are seen as a water leak out of the motor that forms a wet spot or puddle on the ground under the car. Hope this info helps...........

[idosubaru]

When is it overheating - day time, night time, sitting still, moving or both?

If it starts to run hot - pop the hood and see if the fans are running (without letting it overheat obviously).

If it starts to run hot - turn the heater up high - does the air stay hot?

 

That engine requires Subaru's Coolant Conditioner - like $2.50 a bottle.  Was that added?  Probably not the cause of this, but should be done.

[Kassie]

When it overheats it can be day or night, moving or not. The heat continues to blow hot. Conditioner wasn't added(didn't know about it, thanks)

[Rooster2]

When it overheats it can be day or night, moving or not. The heat continues to blow hot. Conditioner wasn't added(didn't know about it, thanks)

The Subaru "conditioner" is simply the marketing term of what Subaru calls their coolant stop leak product, that they advise adding to the cooling system to prevent coolant loss when head gaskets loose their seal. The sealer does a good job of stopping coolant loss, so the engine doesn't over heat due to coolant loss.

[okamikai]

Are the fans working properly? Is the coolant level proper? Air bubbles can make the temp gauge raise and then drop when the coolant passes. Check all cooling lines an hoses; they can crack as they get older and could leak near the fittings. Good Luck

[bajaalt]

I have been having the same problem. When it runs hot I checked and the fans were running. The radiator seemed cold so I was thinking it is the thermostat. It looks like a bitch to replace. Mine is a 04 Baja.

[okamikai]

If the coolant in the radiator is cold with the engine running the thermostat must be stuck, you should avoid driving it like that, the excess heat may warp the heads, the job isn't as hard as you think. 
 
DO NOT DO THIS JOB WITH THE ENGINE HOT, WAIT TILL IT COOLS DOWN! USE SAFETY GLASSES!

 

- Remove the radiator cap and locate the drain plug on the radiator. Remove the coolant (don't toss old coolant down the drain, its ILLEGAL), if you haven't changed the coolant in a long time, do so, old coolant looses its anti-rust chemical properties.

 

- The thermostat should be located at the end of the inlet water hose that goes to the pump, looking from below to your left, you should see the inlet hose attached to the inlet fitting with a hose clamp. You should be able to remove the clamp with a flat head screwdriver. There may be coolant left in the hose and in the engine, when you remove the hose try not to let it fall on you.

 

- The inlet fitting should be screwed in with two 10mm bolts, remove the inlet fitting to expose the thermostat; you should be able to pry it out with the screw driver. At this point you can perform a test on the thermostat, If you wish. You can do this with a lighter of with hot water. Heat the center brass piece of the thermostat and watch if the valve moves, if it does you have a working one, if not, garbage it.

 

- Install the new thermostat (OEM or Original, no cheaps), don't forget the new O-ring, I recommend you use grey silicone to put between the mating surfaces of the inlet fitting and the water pump inlet; make sure NO silicone residues are left inside the inlet or the thermostat.

 

- Tighten the bolts evenly, this will make the silicone set proportionate and will avoid the O-ring from setting down oddly. Wait at least 2 hours to allow the silicone to dry before you put new coolant in the radiator.

 

- Reattach the hose with the hose clamp and refill coolant, make sure to massage the water hoses to remove any air bubbles, to complete this step you may need to run the engine for a few seconds without the radiator cap on so the air bubbles can come out, repeat as necessary until no air bubbles come out.

 

Hopefully this will solve your problem, good luck with the project.

[Gloyale]

FWIW, I repaced a faulty sensor in a 2001 legacy recently.

 

The old ones had two seperate sensors, one for the gauge, one for the ECU.

 

Sometime around 99 they cahnged to one sensor with 2 circuits in it.  This is the type that was in the 2001.

 

 As I warmed up the car the Temp gauge went very high, very quickly...... not immediate, seemed related to engine temp/time running but only idling 5 mins the temp was almost to red.

 

I hooked up the car to a scanner that showed real time data

.The the ECU showed a temp of only 145, not even warm yet.

 

By the time the thermostat opened, and the car was at normal temp......the gauge was PEGGED to the max in the red.  But the ECU only showed 185, and that matched the engine condition which was not steaming or boiling over, not actually overheating at all.

 

In the end, I swapped the sensor on the coolant tube, and all was normal after that.

 

The owner had been to 3 shops, had head gaskets, radiator, thermostat and fans changed to solve "overheating" when in fact it was just a faulty sensor lying to the gauge.  Could have saved himself $2000 in parts and labor.

Edited October 26, 2013 by Gloyale

[Kassie]

Car still not fixed so I'm adding to this "puzzle" with new info.

 

First, the antifreeze is going somewhere BUT the oil looks normal. Whenever I take radiator cap off I hear a whoosh of air and the force of air makes bubbles in my reserve tank (my truck doesn't do this). After changing thermostat and sensor, my heater blew really hot and now it's only warm. Lastly, whenever the heat gauge would rise it would come down after "playing" with heater blower and now when it rises, I have to pull over and let if cool (hope that made sense).

 

Any questions, please ask. I need all help/advice I can get.

[mwatt]

You've tried the inexpensive stuff.  Unfortunately the symptom you describe is the beginning of a headgasket failure.  Exhaust gasses are blowing past a small "break" in one of the headgaskets.  That causes an air pocket to form in the cooling system, resulting in intermittant overheating without any particular pattern to it.

 

My '99 Legacy GT is doing this same thing.....temperature guage will display overheating ONLY when the car is brought to a stop after being on the highway at 75 mph for a while.  When the car is stopped, If I momentarily rev the engine, the temperature guage moves back down, because the coolant circulates faster when the engine is revved. 

 

Headgasket replacement is inevitable.

[okamikai]

I was fearing the same, you should fix this soon; water in the oil can do some serious damage to the engine. the sooner you do this the less it will cost, it cost me around 1,200 dollars because I had to rebuild the entire engine and replace the pistons, and that was me doing the labor. Original gaskets can be around 85 to 95 dollars; repairing, porting, and polishing the heads would cost around 125 dollars for each, change the timing belt (if you haven't done it), kits are sold for around 250 dollars which include everything you need to install it. I hope you can get your car fixed soon.

[Lawsonmh15]

You've tried the inexpensive stuff.  Unfortunately the symptom you describe is the beginning of a headgasket failure.  Exhaust gasses are blowing past a small "break" in one of the headgaskets.  That causes an air pocket to form in the cooling system, resulting in intermittant overheating without any particular pattern to it.

 

My '99 Legacy GT is doing this same thing.....temperature guage will display overheating ONLY when the car is brought to a stop after being on the highway at 75 mph for a while.  When the car is stopped, If I momentarily rev the engine, the temperature guage moves back down, because the coolant circulates faster when the engine is revved. 

 

Headgasket replacement is inevitable.

^^^^^^This.

 

Mine did this exact same thing before mine failed. If you had the coolant drained and filled recently, I'm guessing they didn't do the burp procedure properly and created a bubble. Depending on when it was done, you may still be able to burp it, but...

 

I got the shop that caused the failure to pay for the replacement.

[efseiler]

I thought the redesign they implemented in the latter half of '99 solved that problem in the 2.5L engines but that does kinda sound like a blown HG to me.

 

 

I don't those years of Subaru well but I would get a 2.2L engine put in there if you can.  They are as tough as the toughest Samurai warriors.

 

 

 

--Damien

[bstone]

The first one that I put in was cheapie. The second one(the one installed now) is the best aftermarket my parts store had(around $30)

You need a genuine Subaru part. There's also an aftermarket one that uses the same as the Subaru part, but I can't recall the name.

[Kassie]

I know everyone is telling me head gasket but I haven't replaced it yet, I'm also not driving the car. I have let the car run/idle in my yard and I've noticed a few things.

 

When the temp gauge goes up now, it does not come back down like I earlier posted. It only comes down after letting the engine cool. The radiator will push the coolant out into the reservoir but it will not pull it back in. Also, my heater only blows cold air.

 

Can all if this be due to head gasket??

[Kassie]

One more thing. If I remove my radiator cap the next morning, there's a lot if pressure still on it.

[Rooster2]

I know everyone is telling me head gasket but I haven't replaced it yet, I'm also not driving the car. I have let the car run/idle in my yard and I've noticed a few things.

 

When the temp gauge goes up now, it does not come back down like I earlier posted. It only comes down after letting the engine cool. The radiator will push the coolant out into the reservoir but it will not pull it back in. Also, my heater only blows cold air.

 

Can all if this be due to head gasket??

All classic symptoms of a blown head gasket, especially your writing that the heater only blows cold air.

[Kassie]

Thanks. I guess replacing head gaskets will be the next thing I do.

[okamikai]

There is a replacement for these gaskets on ebay, I found it the other day, some of the members here may know about it, its 100% stainless steel so it shouldn't be affected by rust issues caused by the factory defect, I will be buying one of these to put in my engine as soon as they give up on me. Here's the item, there are a few more, but make sure they are stainless steel of other rust resistant material.

 

http://www.ebay.com/itm/COMETIC-C4264-027-HEAD-GASKET-100MM-027-FOR-SUBARU-EJ25D-EJ251-2458CC-2-5L/121024873762?_trksid=p2047675.m2109&_trkparms=aid%3D555012%26algo%3DPW.MBE%26ao%3D1%26asc%3D18241%26meid%3D2526473997350253807%26pid%3D100010%26prg%3D8344%26rk%3D1%26rkt%3D15%26sd%3D231057871166%26#ht_3756wt_997