Ok, let me lay out all the details.
This has happened a few times and seems to be a completely intermediate problem. But tonight it happened and I made sure to pay full attention to every detail of what was happening.
I was driving down the road and noticed that my heat was not hot. Barely mild. And my temp gauge started climbing. Mostly with rpm but didn't go down when I let off. Then my heat came back intensely, enough to feel like it was burning my hand, and my temp gauge dropped.

Here's some facts:
A couple months ago I put on a timing belt and water pump.
I used nothing but 50/50 premix coolant, no straight water.
The radiator is still full as is the res.
I believe I got all the air pockets out as this has just started over the last 3 weeks or so and only, maybe, once a week. I think one week it did it two days in a row. But it never stays constant.

My question: WTF? I'm thinking the thermostat is sticking or something but I don't want to go digging into that without some opinions first.

 

the term is "intermittent". not intermediate. sorry. i usually don't care enough to correct peoples spelling/grammar. but it's for your benefit.

anywho, if the problem were a stuck t-stat, the heater wouldn't stop blowing hot when the vehicle were already warmed. to me, this definitely sounds like an air pocket. the thing about air pockets is you can have several pockets spread out in the system. eventually, those pockets can gather and form one large pocket. that may explain why you had no problems the first week or so. one place air pockets love to reside? the heater core. this is because the core sits high up in the system and air rises to the top.
bleed the system thoroughly.
at work we have a cooling system evacuator. it seals to the filler neck. you hook up shop air to it and it puts the system under vacuum. you ten use the vacuum to pull your fresh coolant into the system. voila. no chance for any air pockets. this tool also tests for leaks when you leave the system under vacuum for a few minutes. not as good as pressure testing. but will expose any larger leaks. maybe you can rent that tool, or have a shop do it for you. sometimes, you can't get those heater core pockets out without putting it under vacuum

 

sounds like theres not enough coolant in your cooling system,
9 times out of 10 if your heater isnt hot and your temperature guage gets to the hot area it indicate that your low on coolant.

Indicating that either

A you have a coolant leak some were


B your burning coolant.

But you didnt mention smoking out the tail pipe.

SOOOOO im pointing at a coolant leak somewere!!


I use this tool to diagnose my overheating/coolant leak cars.


http://www.ebay.com/itm/Snap-On-Cool...item2a278422c7


it pressurizes the system to find leaks...


and yes it is INTERMITTEN not intermidiate.


sorry for the 5th grade grammar.

 

Did you read where I said both the radiator and reservoir are full?

Nope, coolant has never gone low as I said.

Ah, so you did make an attempt at reading it, I see.

No punctuation, no capitalization, and again nope.


No, intermittenT is the correct term. You just want to feel important.

You are forgiven.


And El crapitan
Thank you for your input. I hadn't considered air pockets merging into a big pocket or that the heater box is elevated. We don't have a vacuum machine at my job only a coolant flush machine that lets the w/p push the coolant out into the used tank and a pump on the machine feeds in fresh coolant. Although, I have never had a problem with air pockets after doing a flush so I might do that.

 

the one we use at work looks similar to this one but this one looks of slightly poorer quality. the only other one i could find was mityvac. and that one is even cheaper looking.
i can't recall the brand now. but it is exactly the same idea as this:
http://www.ebay.com/itm/Uview-550000...-/230450066489

if you work in the trade, i urge you to pick one up. it is so much faster to refill when you're pulling it in with vacuum instead of pouring. if you leave it under vacuum, it also does a quick and dirty leak check after you've worked on the system. and, of course, evacuates all air from the system.
excellent tool. well worth the price

 

Well, it started doing it again on the way home tonight so as soon as I pulled up to my house I popped the hood and went in to grab a 12mm. I cracked open the bleeder and sure enough there was more air that hadn't came out when I bled it after the new w/p.