Hi guys this car is beginning to kick my hind end. Wife was driving from phx to flag and there is a pretty good grade coming north. After creating the grade the temp light began to flash. Looked at it differance in hose temp....changed cap and thermostat. Whent back to phx same thing cam up grade and light started blinking. Also when it does this it pukes coolant from the overflow tank everywere. Tried to "burp" system. When down to phx and it bean doing it going down the hill. Talked to local subui guy and sugested radiator. Put in new radiator, still puking coolant out the overflow. ......which leaves head gaskets or waterpump. Put a block tester on today and couldn't get it to do much, still seemed to remain blue. Is it possible a waterpump could be giving me all this greif? Or do I need to keep testing for head gaskets? Any help would be great. Oh and when I did the block test ran for approx 20 min and removed some of the coolant so as not to get a poor result

Kinda sounds head gaskety.

Block test don't work on these.

Need a leak-down test to confirm a bad head gasket.

 

Shouldn't have any real problem getting air out of that engine. Fill it, let it run until the cooling fans cycle on and back off and the thermostat opens, then turn it off and let it cool. Top off if necessary.

 

Thermostat should be Subaru OE or an OE similar design. The cheapos can cause more problems.

Well here is some more info. If you start the car, take the cap off it wants to start pushing coolant out the top of the radiator. Not sure if that's normal, never paid much attention to it. I don't see any bu bled in the overflow, or milky oil. My gut says head gasket but don't want to go down that road unless it completely nessiary.

Also on the thermostat both upper and lower hose seem the be fairly compatible in temputure unless the little air valve in the thermostat is faulty

Ever had the engine overheat before this happened?  If so, the heads could have warped causing a premature head gasket failure.

 

Was any work done on the head gaskets before?

No head work, just timing belt, thermostat (not oem) if it turn out to be head gaskets can I mill the heads.

Also what is the most definite way to rule out head gaskets. Since a block test won't work on these

First off, only use a OEM thermostat.

 

If it is the head gaskets, then you can check the decks for warpage using a machinist's straight edge.  If out of spec ( >0.0025") , then a machine shop will have to machine the heads flat.

 

From your description of things, overheating and 'puking' coolant out of the overflow tank points to head gasket failure.

Well here is some more info. If you start the car, take the cap off it wants to start pushing coolant out the top of the radiator. Not sure if that's normal, never paid much attention to it. I don't see any bu bled in the overflow, or milky oil. My gut says head gasket but don't want to go down that road unless it completely nessiary.

All cars with cap removed will start pushing coolant out the top of the rad, so seeing that is not telling you that anything is amiss.

 

Suggest you replace the thermostat with an OEM unit from Subaru. That may well fix the problem, if not, then head gasket problem is next best guess. On your 2010 model, it is not known for a bad head gasket causing over heating by exhaust gas entering the cooling system. If head gasket goes bad on your model, it causes a coolant leak, that then causes over heating because the coolant level is low in the cooling system. Have you ever seen coolant leakage on your garage floor, or elsewhere where car is parked after driving it for a while??

Crawled under car and looked for the tell tale coolant leak between engine and head, no coolant leaking. No drips on driveway. Just pukes it out once it gets hot.

A little more food for thought is it is appointment 130 miles from flag to pheonix. The car acts fine just put zing around but once you drive it for a prolonged period of time it tends to act up.

First, follow Roster 2's advice.  Second, is the car a NA 2.5?  If so, it has the new MLS HG's, and it should not have a HG problem? So we will be interested in follow up on it.

Make sure it's not slowly getting low due to an external leak and then overheating when it's low on coolant.

 

If you replace the head gaskets just resurface the heads no matter what. It's pointless to check for "warp" because you want the proper finish and they all have high and low spots on the surface anyway. And Subaru heads don't warp anyway unless you install a supercharger and run it overheating til it stops. Lol

 

You can resurface yourself if you're doing the head gaskets yourself it's really easy actually. Read thread on here about it.

Thanks for all the help, I will put the oem thermostat in the car and see what that does. Would have never bought the brand. X if I had known that it could possibly cause me headaches.

Well I think I just got my answer today. Put new OEM subaru thermostat and got burp funnel filled overflow to full line drove home , approx 20 miles and opened hood when I got home and saw the dreded bubbles in overflow, which also rose from previous level.....so yes a 2010 with the mls head gaskets can fail at 130,000 miles. Very dissapointed but still best car for snow. So I will be pulling an engine and doing my fist set of subaru head gaskets.

Might be a silly question....But have you pressure tested the cap? 

 

your coolant system needs to remain air tight in order to work. It doesnt sound like you have even looked at that possibility.

New oem subaru cap as well.

Resurface the heads. These never warp but will have high and low spots and not ideal roughness.

 

They're cheap and easy but For all the radiator cap comments seen online it's unlikely.