Temperature spike on my '05 LLY

[rapidoxidationman]

70 degree day, 55mph, level ground, not towing, cruise control set, no A/C running.
Looked down and the DIC said something like "coolant temperature high" and sure enough, it was only a couple of notches below 260. Tapped the brake, and turned the heat up to HIGH and watched the guage move to below 210 in about 5 seconds.
Pulled over and opened the hood and saw no coolant leaks, no steam, and the expansion tank had coolant about 3/4" above the seam molded into the tank.
hmmm
Got back in and continued driving while paying attention to the temp guage and watched it dance between 1/4 scale and just below 210.
A close eye on it for the rest of the day (lots of starting and shutdown cycles) saw the guage moving a lot - it rises to close to 210 after starting up then you can see that the t-stats open and the temp drops quickly to 1/4 scale...

Right now I'm wondering if
A) the temp sending unit is going bad or
B) the new thermostats I installed in January while doing the head gaskets are somehow sticking

This is the first time in 1.5 years of owning the truck I've seen the guage go above half, and that includes a lot of time driving around with a bad head gasket.


Any ideas from the forum?

[DmaxMaverick]

A and/or B. Or significant air in the system (it must be properly bled), but not likely if your coolant level is stable.

The PCM is seeing the high temp indication (the reason for the message), so the gage is probably displaying what it's told to display.

Sticky stats can cause this. So can a bad sender. Pick one. You could install a mechanical temp gage to verify what is actually going on. This would allow you to eliminate whichever is working correctly. A gage is cheaper than the sender, or a set of stats.

[rapidoxidationman]

Quick response, thanks!
I've got an infrared thermometer gun in the toolbag, and meant to shoot the thermostat housing at some point today but work kept getting in the way. Where does the temp sending unit mount? IIRC it is on the thermostat housing, but I'm not sure. Tomorrow at the top of Teton Pass I'll pull over and see if the guage agrees with the gun and go from there.

I just stepped outside to take a quick look under the hood again (truck has been off for 5 hours) and had only a very small residual pressure in the pressure tank. The engine was still warm so I'll chalk that up to thermal expansion (and not a new leak in a head gasket...). Squeezing the upper radiator hose gave me no sloshing sounds like air in the system and I could hear the t-stats clicking in the current of fluid I generated.

[rapidoxidationman]

as the temp guage spikes the heater blows cold. When the guage starts to recede the heater begins to blow HOT again.

Picked up the two OEM thermostats ($90:() today and will be replacing them tonight.

[DmaxMaverick]

Sounds like air in the system. If it wasn't, the heater wouldn't be blowing cold when it shouldn't. Start cold, remove the reservoir cap and watch for bubbles and/or surging of the coolant level. If it bubbles or surges, you may have a combustion gas leak. Otherwise, it is probably just low and not bled properly.

[rapidoxidationman]

It does sound like air in the system, but I'm not seeing any residual pressure like I did before I did my head gaskets.
Not losing any coolant either, haven't had to add any since completing the HG job and when I open the expansion tank cap there's no surge of bubbles from the cooling system like prior to replacing the head gaskets.
On starting up cold, the temp will spike then settle down to between 1/4 and 1/2 scale on the temp guage. During the spike the heater will not have hot air then something happens and the heater blows hot and the temp settles down and wont go high again until the next startup.

Is there a valve in the cooling system besides the thermostats? I'll be studying AllDataDIY to find the answer myself, but if anybody knows I'm all ears.
I just replaced the thermostats tonight - an easy hour's worth of work in the driveway. Hoping tomorrow shows things all better, but I'm still going to study tonight.

All ideas welcome.

[DmaxMaverick]

Since you have Alldata, revisit it and follow the coolant system bleed instructions, EXACTLY. If it were your stats, the heater would still blow hot when the temp increases. If the heater isn't hot, that means the coolant is cold, or there's no coolant passing. The heater is on a bypass from the pump, so it should never be cold, once hot. Only air or no-flow will do that.

[Kennedy]

Fan clutch could well be the culprit, but on the same note this would not typically affect the hot/cold in the heater. Maybe boiling due to low pressure is creating the air?

[rapidoxidationman]

As I sit here waiting for the flatbed to come and haul my sorry butt back over Teton Pass to my friendly Subaru shop, I find myself fairly convinced that a head gasket has indeed let go. This is deduced by the 5 second geyser of coolant that erupted from the expansion tank when I (perhaps foolishly) loosened the cap a bit when it was hot.
So... where's that list of parts I need?...
Argh.
The cooling fan clutch does grab when the radiator heats up...
I honestly did not perceive air in the system over the past few days. I was onvinced (until an hour ago) that the thermostat bypass tube was somehow plugged.

[DmaxMaverick]

OK. Sorry to hear that. What's the rest of the story? Did you recently replace the HG's?

[rapidoxidationman]

Yup
http://www.thedieselpageforums.com/tdpforum/showthread.php?t=39924
Never did finish writing up the play by play... Maybe this is the universe's way of telling me to get on it:confused:

An interesting ride home via flatbed tow truck. The driver held a (mostly one sided) conversation about the difference between ChemTrails and ConTrails (Jetliner exhaust), OBummer, 911 and Building 7, religion and the end of times, corporate control of the human race, UN and world population control, intentional spread of HIV/HepC/cancer, how digital TV's can transmit as well as receive, how cell phones are watching you, and the list goes on... Infowars.com he says. Hmmmm Ok. I looked for his roll of tinfoil that he makes the hats out of but his boss must've said to keep it under the seat..;)

Looks like I'll start tearing down the engine again tomorrow evening. Damn. I really thought I had it nailed; the coolant level and the temperatures haven't budged since January until this Tuesday.
Are those $600 ARP head studs reuseable? (serious question...)

In the meantime, didja know that cream soda and Meyers Dark rum go REALLY well together?

Time to take a shower and wash all this dexcool off me.
Cheers!
Guy

[DmaxMaverick]

Sounds like an interesting ride. How's that go? "You're only paranoid if they're not after you...."

Yeah. The head studs are reusable. That's one beauty of them. You should only be in for gaskets, sealer, and a fresh supply of four-letter-words. I know most folks don't do it, but there's a reason they recommend stud torquing at least once after so many heat cycles. I'm curious to know why, if the gasket failed.