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....

This sounds similar to a problem I am currently having with my 99 outback. Running warm at sustained 65 MPH (~2500 RPMs), but punch it up to about 72 MPH (~3000 RPMs), and the coolant temp drops for a while. Same deal, new headgaskets, t-stat, water pump - and my mechanic says they use a system of filling it that prevents air bubbles, so that shouldn't be it. Have you tried elevating the front end and adding coolant till it flows out the vent plug hole? Just after it runs hot, does it show any signs of bubbling in the surge tank? What brand t-stat and water pump did you use?

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?

Oh - forgot to mention. Fans run fine too.

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!!