Help with civic running hot

01 Honda Civic when idling the temperature climbs. Heat blows cold. Raise idle to 2000 and above heat blows hot, temperature goes to normal.

I changed the thermostat about a month ago because the temperature would raise and fall like the thermostat wasn't opening all the way. 
 

Problem returned today only worse. Is it possible that the impeller on the water pump is damaged in someway that it won't flow enough water at idle?

Car is due for a TB and WP I've just been putting it off.

I was really hoping used car prices would go back to down since this car needs replaced for other reasons as well. Not a good time to spent $ now.

As always, thanks!

I had a Buick somehow have the impeller on its water pump degrade to looking like a Chinese throwing star. Most impellers are steel and could possibly rust if there's been a problem with the coolant.

I think those have water pumps intended to be replaced with the timing belt at something like 65K miles. I'd start there.

The other possibility is low coolant level / air pockets in the cooling system. I'd check that before deep diving on the water pump and timing belt.

7th gen Civic with the D17, probably a head gasket, which seem to affect almost all of them. It is a matter of when it happens. The two in my family all had them done within 200k to 230k mile range. Others have had it happen at miles higher and lower than the two that I had done. 

In reply to aw614 :

That was my thought but I don't see any telltale signs of blown head gasket. No contaminated oil or coolant. Coolant doesn't shoot out of cap when running. No white smoke.
 

Any other way to check for HG failure?

Chk for combustion gasses in the coolant.  there are test kits for that.  Or you can get a cooling system pressure tester (you may be able to "rent" a free one at the local parts store)  Pressurize the cooling system and see if it holds pressure over light.  

Civics are a pain in the tookus to get the air out.  The radiators are pretty low.  I forget, but I think they have a bleed on the stat neck, don't they?

And yes, water pump impellers are notorious for failing.  Since the "correct" procedure is to replace the water pump with every timing belt job, I get the impression that the water pumps are engineered knowing they don't need to last long.

I think:  air bubble and bad pump are where I'd look first.

Last night I pressurized the cooling system. Started at 16 psi (1.1 bar). After 12 hours, pressure dropped to 13.5 psi. Does this mean the HG is bad or is this an acceptable loss after this timeframe?

BTW I don't believe there is a bleeder valve in the system. At least, I know it's not on the thermostat housing.

That little pressure loss over 12 hours could be a leak in the pressure tester or a pinhole in a hose/radiator.  A busted head gasket would likely leak down to zero in an hour or less.

rustybugkiller said:

In reply to aw614 :

 

That was my thought but I don't see any telltale signs of blown head gasket. No contaminated oil or coolant. Coolant doesn't shoot out of cap when running. No white smoke.
 

Any other way to check for HG failure?

Civicforums has a decent list to look for, if you can look for posts by ezone about it, they are informative on the issue:

https://www.civicforums.com/forums/331-overheating-loss-coolant-heater-blowing-cold/340759-overheating-mysterious-coolant-loss-common-causes-reference.html

The D17 has headgasket failures even without the common symptoms. In the cases of mine, on the 2002 it was coolant loss, but no visible smoke. It didn't push coolant out to the overflow tank, it just disappeared. The first instance of overheating happened around 150k miles, missing coolant, somehow got it to last 70k miles more by hawking over the coolant and making sure my non mechnically inclined brother had coolant in his car every 2 weeks. Sadly the time I drove it, I did not check the coolant and it overheated on me on the way home from work. 

On 04, at around 195kish, it just started pushing coolant to the overflow, but it never actually overheated, so eventually got the hg done on it. 

Honestly, if you stick with a 7th gen, the headgaskets are maintenance items if you plan to keep it for a long time.

Read title. Thought head gasket. 
 

Read thread

still think head gasket. 

After reading the info from aw614, I pretty sure I have a slow HG leak.

Problem is the car has had a transmission issue for sometime that I have been babying until the market changes.  Changing a HG is not worth my time at this point. I can use my truck for awhile but I need a dd that's  easy on gas. I'm tempted to try liquid HG repair while I searching for my next dd. 

If the thermal water switch is in a location on top of the engine, remove the switch to get air out.  My BIL had a Civic  (I have forgotten the year) and it did not have a bleeder screw on the upper water neck.  I removed the thermal water switch to bleed it and put it back in.  I do not know if that is an approved method or not, but it worked for me.

#17 in this picture.