On a cold engine, I noticed the coolant in the reservoir was at the minimum line, so I topped it off to the max line. This was about one week ago.

Yesterday I went for a 15 mile drive up a mountain road. When I arrived, my coolant had risen to the very top of the reservoir and was overflowing. There were no sings of overheating.

Did i overfill the reservoir?
Was it normal for the coolant level to be at the bottom line?

I'm guessing I should've left it alone as the coolant expands and contracts under use.

 

Yup on almost all accounts. At an ambient air temp of around 70º the level should be about mid point on the tank. Given your cooling system is working properly (it's a good idea to change the radiator cap every 3-4 years) the level will rise when the engine is shut off and the temp and pressure spikes. As the engine/radiator cool it will siphon the fluid back from the tank. As a fluid, the coolant does not expand or contract unless vapor (air) is in the system.

 

you have a real problem,,, but it didnt start with the res bottle
That should be at MIN when COLD

the uphill trip puts a load on system, if cap has weak seal as suggested above, or clogged radiator or other cooling probs--it will show up then
AT NO TIME should it come out the res, and never under pressure
That means an overpressure in the system for some reason

Has the water pump been replaced?
age of coolant- more than 5 years?

ck cap and pressure test rad and cooling system

my 01 doesnt change level like that in hard drive

 

no temp guage change from its normal 1-2 lines below half ??? and always stable?

 

True-if a Honda is overheating something is wrong.

 

The temp gauge is always stable.

It had the 105k service done at the dealer. The water pump is replaced then, correct? I don't know for sure; I'd have to get records.

The coolant is a few years old. I was planning to change it after winter.

I replaced the radiator cap about two years ago, albeit with an aftermarket from autozone.

As for a pressure test, I see the manual shows a pressure tester. Is that the only way to do it?

Also, just to clarify the coolant wasn't gushing out of the reservoir, it had simply leaked out the top.

 

I should start with a new cap I suppose...

 

its not supposed to rise up and come out the res cap at all-ever

I suspect the thermostat is sticking or the rad is dirty
OR most common is fan coolant temp sensor A is bad
the driver side fan wont come on when needed, and will run for several minutes after shutdown with normal temp showing.
Normal operation is 2 minutes max run time after engine off
Note: the guage is not all knowing of true temp and can be fooled

Pressure tester avail for loan at parts stores
They can test cap for you as well

Yes the 105 is the new water pump and timing belt, it gets new coolant then.
should replace coolant every 5 years MAX

 

Just got my radiator flushed today, kind of ironic this thread popped up

 

I disagree. Did you read the original post? He overfilled the overflow with the engine cold. When the engine heats up, the coolant will rise and push the excess out of the overflow. If you fill the overflow to the cold line, it will usually be at or near the hot line at normal operating temperature. Sounds like he had no cooling system problems before and I doubt he has any now. Certainly not based on this one symptom.

 

That makes sense to me. If the syst. is full & there is an excess introduced into it when cold, it has to go somewhere when it gets hot.

Just keep close tabs on the temp. gauge and coolant level for a while; it will probably be fine. You didn't have a cooling issue prior to adding coolant to the resv., right?

 

Negative, no issues prior.

My gut feeling is that I just overfilled. Should I dump some coolant out from the reservoir down to the lower line? It's currently well above the max line, over 3/4 full with a cold engine.

I'm going to do a pressure test later today.

Thanks for your help so far guys.

 

^^^ I would, although it will seek it's own level eventually. If you do it, it'll be less messy. I'd put an o.e. cap on also for no real reason other my snobbish opinion of some aftermarket parts/parts stores.