Engine running warm after new headgaskets

[bcward]

Ok - 99 Outback with 2.5 DOHC (Phase I), 114k miles. Car is relatively new to us, but ran great in town and short (<15 miles) highway trips. Recently replaced the timing belt, idlers, water pump, t-stat, since it was overdue and hadn't been done as far as I could tell. In road testing after this work, I noticed spiking temperatures (never overheated, but would spike pretty close to H and I would shut down immediately out of panic). At first I thought it was air in the system, but I was careful about filling it the first time and burped it. Tried to burp it again for good measure - no luck. Replaced new thermostat with another brand new thermostat, replaced coolant, burped. Same thing. Gave up and took it to a shop - they diagnosed combustion gases in coolant at higher RPMs (also some black gunk), so this seemed reasonable given everything HGs posted for this engine. The old headgaskets did show some signs of likely leakage. Had the heads milled flat too. They refilled coolant after HG job, thoroughly burped, and road tested - it all checked out OK according to them.

 

Now here is the weird part: After about 15 minutes highway driving on slight incline, coolant heat says that it is running a bit warm. Very slow increase, not like previous spiking. Its normal spot is just below half, as far as I can tell. Replaced radiator cap, but problem continued. Gradual buildup of heat over many miles at <=2500 RPM (either in town or on highway). I eventually figured out that if I bump it just over 3000 RPM, the temperature would drop like someone flicked a switch (in seconds, not the minutes it took to heat up). Running at 2500 RPM, even downhill with a COLD headwind, it still wanted to run warm. Bump it up to 3000 for a few seconds, temperature returns to normal, and would stay that way for several miles. I replicated this result many times on a 500 mile trip we did this weekend.

 

All this took place when air temp is in the single digits - should I be terrified when summer comes?

 

Any ideas?

 

Does this indicate a bad t-stat, water pump, engine ? Or have I lost it and this is normal for this era of engine?? It doesn't rise about 3/4 of the way above the guage (though I don't let it - I either crank the cabin heat up or do the 3000 RPM trick to pull it back down). Our EJ22 on our older car sticks right at its normal temp through almost any road conditions.

 

FYI - oil looks great. Coolant level in reservoir looks great. Coolant level in radiator looks great. No signs of leakage of any coolant. And there were no signs of bubbles in the coolant tank after it was wanting to run warm. No signs of black gunk either. Lower radiator hose was cool, not cold.

 

Thanks!!

[bcward]

Oh - forgot to mention. Fans run fine too.

[Manarius]

I think you said it yourself. The lower hose was cold. To me, that indicates a Thermostat not opening to send the coolant through the radiator. I think it's time to replace your T-Stat with a new OEM one (yes, OEM is required for this sort of item).

[nipper]

Did you have the radiator cleaned after the HG was replaced. Oil plus antifreeze make goo and clogs the radiator. this is not an uncommon problem, depending upon how badly the HG leaked and for how long.

 

nipper

[Wayne Boncyk]

Nipper's right - based on my experience. Do a good flush of the system and, as others have suggested, replace your T'stat with a Subaru OEM. You either have gunk in the radiator, or a T'stat that got a little too stressed when the HGs blew, or both. In my case, it was both!

[bcward]

Since it is on it's 3rd round of fresh coolant in 3 weeks, I'd suspect the coolant system is pretty well flushed by now, if there was any gunk in the system. From what I was able to learn, there was no oil and coolant mixing, just combustion gases blowing into the coolant which would produce some small black chunks rather than thick slime. The shop I took it too said the HG leak was pretty small rather than extreme.

 

It is running on the second brand-new thermostat, though I'll admit that it is a motorad thermostat (aftermarket?) rather than one purchased from the dealer.

 

Though what I don't understand is that if it is a bad thermostat (i.e., opening only at higher temps), why did coolant temp decrease quickly right at 3000 RPM? If it was bad, I'd suspect it would want to overheat and stay that way.

 

My mechanic suggested that the coolant temp sensor may be screwy - has anyone had experience with this, and has it produced similar results?

[nipper]

Your making a poor assumption. There is no detergent in antifreeze. You can change fluid 30 times and the gunk will still be there unless you run dawn through the radiator.

 

 

Was the 3000 rpm under load or the car parked?

 

 

nipper

[hankosolder2]

Tough what I don't understand is that if it is a bad thermostat (i.e., opening only at higher temps), why did coolant temp decrease quickly right at 3000 RPM? If it was bad, I'd suspect it would want to overheat and stay that way.

 

My mechanic suggested that the coolant temp sensor may be screwy - has anyone had experience with this, and has it produced similar results?

 

I have seen problems with the coolant temp sensor (on BMWs, not subies) where a one degree difference in actual coolant temp can cause a vast difference in the gauge readings. You could monitor the temp by other means or just change the sensor (the one for the gauge, not the one for the engine control computer) and see what happens.

 

I second replacing the thermostat with oem. Perhaps the water pump is sucking a bit harder at higher RPMS and is forcing a slightly sticky T-stat to open fractionally more. (Clutching at straws here.)

 

Checking the radiator for proper flow (as others have suggested) can't hurt either.

 

Best of luck,

Nathan

[fubar]

Check the lower rad hose.If it's old it could be collapsing and restricting flow.Possibly at about 3K rpm the flow may be overcoming the restriction. Also, I beleive it's possible to install the t-stat backwards. Use an OEM t-stat they have a nice jiggle valve to help burp the system at least in my 91.

[richierich]

As owner of a Suby shop, people always ask why do we have to do the radiator? I tell them, it is 8+ years old and has had oil running through it. If they still have questions, show then how cheesy the radiator is, and say if you overheat it, and its the radiator, I will not pay for all of the repairs. I think they are like $159 bucks.

[nipper]

When i go my engine rebuilt, they rodded the radiator for 100 bucks also. they said they do that with any rebuild or HG job if the car has over 100K on it for the same reason, its insurance.

 

nipper

[bcward]

Ok - I concede - it could be the radiator, since I did not replace it, or flush it with dawn (nipper - would you really do that?) and it may have gunk in it from either the HG problem or just being old.

 

But, before I throw more money at it, I'm trying to understand why I'd see the pattern I'm seeing. If it was a thermostat that was completely stuck, I'd expect it to want to overheat and stay that way, unless I take the load off and coast downhill with a COLD head wind (which I did, and temperature didn't go down). If it opens at too high a temperature, then I'd expect the engine to run warm and stay that way, never returning to that spot just below half (which it does after 3000 RPM surge). If it was the radiator, I'd expect either the lower hose to be warm if the radiator isn't cooling effectively, or for the engine to run warm all the time if it is plugged (didn't seem plugged, drained and filled just fine), just like a stuck thermostat, right?

 

So why the pattern of gradual warming and then a few seconds at 3000 RPM to cool it down? Is this enough coolant pressure to force coolant through a gummed up radiator, thus allowing it actually cool the coolant? If so, I'd expect it to take longer for the coolant temperature to drop.

 

Thanks guys for all your thoughts on this! I'm just trying to avoid throwing more money at this thing until I understand what it might be and why - the HG job definitely was a pinch I wasn't prepared for!

 

Does anyone know if anything special happens in these engines at 3000 RPMs? The effect I'm seeing is like someone flipped a switch....

[86ruguy]

i realize that you are dealing with a different engine and such but when i put the 2.2 out of my swap car into my 92 legacy, i had a small leak in one of the heater hoses ( bear with me for a second) hence i had coolant lacking in the heater core. i also have had air stuck in the heater core because the hoses were backwards on the engine side. hence, with the air bubble in the core it was overheating.

 

i have learned that these cars take a REALLY LONG time to burp all the air out. i have one of the radiator fill adapters and it took me about 30 minutes to burp the legacy.

 

just my .02

[nipper]

Ok - I concede - it could be the radiator, since I did not replace it, or flush it with dawn (nipper - would you really do that?) and it may have gunk in it from either the HG problem or just being old.

 

But, before I throw more money at it, I'm trying to understand why I'd see the pattern I'm seeing. If it was a thermostat that was completely stuck, I'd expect it to want to overheat and stay that way, unless I take the load off and coast downhill with a COLD head wind (which I did, and temperature didn't go down). If it opens at too high a temperature, then I'd expect the engine to run warm and stay that way, never returning to that spot just below half (which it does after 3000 RPM surge). If it was the radiator, I'd expect either the lower hose to be warm if the radiator isn't cooling effectively, or for the engine to run warm all the time if it is plugged (didn't seem plugged, drained and filled just fine), just like a stuck thermostat, right?

 

So why the pattern of gradual warming and then a few seconds at 3000 RPM to cool it down? Is this enough coolant pressure to force coolant through a gummed up radiator, thus allowing it actually cool the coolant? If so, I'd expect it to take longer for the coolant temperature to drop.

 

Thanks guys for all your thoughts on this! I'm just trying to avoid throwing more money at this thing until I understand what it might be and why - the HG job definitely was a pinch I wasn't prepared for!

 

Does anyone know if anything special happens in these engines at 3000 RPMs? The effect I'm seeing is like someone flipped a switch....

 

 

Thgermostates can only partially open, as they are simple bumetalic springs. Its not an uncommon failure mode.

 

Your not looking at pressure, your looking at flow. Caps make the pressure, not the pump.

 

There are entire courses dedicated to the behaviors of liquids and laminar flow, so i cant really go into detail here on why its doing what its doing, but you have the right idea.

Liquids are called non compressable gasses for the purpose of enginnering and flow. Both liquids and gases behave the same when you are talking about flow.

There is some point in flow where you have enough fluid passing through the radiator passeges to cool down the car, and right now they way your radiator is clogged thats at 3000 rpm.

If your radiator was clogged in the normal fashion, then your assumption would be correct.

 

To clean the goo out you have to remove the coolant hoses and run dwn through the radiator. i always found this is easier to do with the raditor out of the car (Use warm water initially then rinse with a hose).

 

Clogged raditors can have odd behavior.

 

nipper

[MDW25gt]

I dont like the idea of flushing the entire system with the marginal head gasket design. When I do it in the spring, I believe I will pull the radiator out and have it cleaned. per Nip's reco.