OK, for the second time in about a month, I've had the coolant temp shoot up and stay high.

The first time I only noticed just before I parked, and it was at 205*. I shut it down, poked around checking coolant level, and that the fan was working. Both were fine, but when I turned it back on, the temp showed no signs of coming down, even with the fan going on a 45* day. Turned it off, got my sandwich from the store, came back out, and it was still at 200, but rapidly dropped and went back to 180* and stayed there.

Second time was this evening. Same thing, went up to 210* stayed there for a while, then came back down to 185*, but wouldn't go down any closer to the 180* it usually runs at. Outside temp was 35*

Has a 180* T-stat, undrilled, and fan points are set for that. Usually the car will get up to heat at 180* very quickly, drop when the T-stat opens the first time, then come back up and steady off at 180*.

Could it just be I need a new T-stat, or is something else going on here?

When you checked the coolant level, did you check it in the radiator also, or just the expansion tank? If the coolant level is ok in the radiator, I'd start with a new thermostat. It'* quick, easy, and cheap. That would be my initial suspect.

Oh, damn, no I didn't.
I'll check it next time I go out. Thanks, Archon.

Sorry, should have got back to this earlier. Checked radiator, washed coolant off hands. Yup, it'* full...
I'll run up to INTENSE tomorrow and pick up the T-stat and gaskets. If it persists after that, I'll dig this one up again...

OK, cool. I've had a couple of radiator caps go bad on some cars that have left the expansion tank where it belonged, but allowed coolant to be dumped from the radiator. If the thermostat doesn't do it, check for collapsing radiator hoses when the engine is revved a bit. That will cause a similar problem.

or check all your hose clamps hooked up to the cooling system

but if that doesnt work and the t stat doesnt either i dont know wat to tell you

do your cooling fans come on :?

didnt read your first post clearly

so if the cooling fans are working it sounds to me like the t stat isnt working good enough

or you have a coolant leak
are you droping any on the ground where you park :?

i hate over heating and coolant problems

It'* freaking freezing here...I'm wussing out, car goes to INTENSE...they have a heated work area...

OK, changed T-stat, still got the problem...
I'm thinking fan now...I'm just gonna take the damn thing to the dealer.

Your description sounds like what can happen with an air bubble trapped in the intake. Is your thermostat drilled? And did you re-fill the engine at the thermostat opening as described here?: http://www.bonnevilleclub.com/forum/...=article&k=100 The procedure says it is for the L36, but is also applicable to your L67.

Now, that said, for trapped air to be the problem, it had to have gotten in to the engine somehow; either by the cooling system being opened to change a component, then not properly bled, or by an internal or external coolant leak.

A coolant leak can be inferred by checking the coolant level in the radiator and the overflow tank under the same (engine cold) conditions periodically. The same conditions are necessary because coolant expands when it gets hot and contracts when it cools, changing the apparent level. And, a bad radiator cap or leaking overflow hose can impair the flow of coolant in and out of the overflow tank. (I'm guessing that'* why Archon asked you to check the radiator.)

Other less-likely possibilities for your symptoms include a water pump with an eroded or slipping impeller, a bad gauge or gauge circuit, or an electrical problem like an intermittent short causing a false gauge reading.