Overflowing antifreeze reservoir
 

I've been dealing with an issue of my antifreeze reservoir overflowing and leaving the system low on antifreeze.

I've been searching all over for the answer to the problem everything is saying it is the headgasket but none of the tests I've done can confirm this. I've only had it get hot 3 times. The first was after removing the throttle body and cleaning it and didn't burp the system. Than the second time was 6 to 8 months later after a long drive, after it cooled down the reservoir lowered and I topped off the radiator. When I got home I changed the radiator cap and thermostat. The last time was about 3 weeks after that so I changed the radiator and hoses.

I can tell right before it happens because the idle become really rough. Today when I went to check the fluid level I opened the radiator cap and the reservoir overflowed and the radiator is low again.

• No milky oil.
• No smoke from exhaust.
• Compression was even across all cylinders, one cylinder was 2 PSI lower. I did this with a cold and a hot engine.
• Bottom hose warms up once up to temp.

• I've change the radiator, old one was plugged up, and flushed the system
• Change radiator cap, aftermarket
• Change thermostat, aftermarket

I saw one more test that I can run with shop air, but my air compressor will only go up to 120PSI will that be enough pressure? Also I've been reading that the thermostat and radiator cap should be from honda not aftermarket, could that make a differance?

Thanks for the help.

Re: Overflowing antifreeze reservoir
 

do the shop air test, that will show you that its the head gasket.

Re: Overflowing antifreeze reservoir
 

Thanks that's what I thought. What PSI is recommended. I'm assuming my 120 PSI compressor isn't enough.

Re: Overflowing antifreeze reservoir
 

I'm not sure off the top of my head. There's a couple threads that are stickied that have the exact procedure in them.

Re: Overflowing antifreeze reservoir
 

I had a Toyota doing it and it only done it as the coolant got cool from being hot and the pressure dropped. Hoped you used a factory thermostat. After market is junk and that little vent in the cap is what vents to pull coolant in when system cools off to keep engine full of coolant. A bad cap will cause problem. Had this problem on an old IronDuke 4 cyl Olds. Was watching it and it actually sucked bottom radiator hose flat. Make sure thermostat and cap are new OEM. Pressure test radiator. Put some name brand stop leak in it. Pressure test each cylinder building pressure slowly.

Re: Overflowing antifreeze reservoir
 

I didn't use oem for the thermostat or radiator cap. The radiator I got from a place that sells oem parts. I will try all suggestions as soon as I can. Thanks for the help. I'll post back after each test.

Re: Overflowing antifreeze reservoir
 

120 PSI could be enough. Depends on the severity of the breach.

Re: Overflowing antifreeze reservoir
 

As long as radiator does not leak at main seal and of course anywhere else, non OEM is OK. The cap and the thermostat should be OEM since you are having problems, so you can to rule them out as to not being a problem. Just my opinion.

Re: Overflowing antifreeze reservoir
 

Thanks. I just got the thermostat and radiator cap from honda Today. I'm going to change them tomorrow.

Also a not. After I took the radiator cap off yesterday and the reservoir over flowed. The reservoir emptied into the radiator.

Re: Overflowing antifreeze reservoir
 

How full are you filling the coolant reservoir?
If you fill it to the top it WILL overflow as the engine heats up (hot liquid expands).

The MAX line is a ways down the bottle.

Re: Overflowing antifreeze reservoir
 

It was at the max line when cold when I started. I think the radiator cap isn't letting it pull back in. After I releaved the pressure yesterday it went back into The radiator.

Re: Overflowing antifreeze reservoir
 

Did you put the Honda radiator cap on yet?


Will the aftermarket radiator accept a stock cap?

Re: Overflowing antifreeze reservoir
 

Not yet will do that tomorrow. And it should

Re: Overflowing antifreeze reservoir
 

i didnt have a blown heagasket , but mine i think was blown where the part of the egr assybly bolts to the head .. there is coolant going in there..

this summer i passed all tests cylinder leakage.. by searching i found the answer.. and yet I was missing coolant every once in a while...

that was the culprit.. good thing i blew my valves aparts so i had to do not just that part but the whole headgasket..

Re: Overflowing antifreeze reservoir
 

There is two seals in the radiator cap. The little small one in the top works on the same principle as why a mason jar when it cools down seals and sucks the lid down. The engine has to cool down to suck the fluid back in. However, it really should not be low and you have some problem for sure. I could be wrong here but in normal driving, there really should not be fluid coming into the plastic tank. Maybe hauling a trailer up Pike's Peak would do it. My Tacoma never uses the tank fluid. My CRV has always used a little since new. Not much however and it's a 2005.

Re: Overflowing antifreeze reservoir
 

Fluid level in the reservoir will change, rise as the engine heats up and drop as the engine cools off. (Provided the cooling system is properly filled/burped, no air pockets, and none of the hoses balloon under pressure)
Laws of Physics, heat=expansion and all that.

It should always return to its starting point when the engine cools though.

Most Hondas do seem to need reservoirs topped up from time to time, that's normal IMO if it's like several thousand miles between top ups.
Sometimes it seems as though I'm the only one in the shop who does top them up during an oil change.

I'd think the cooling system under a slight vacuum could make the radiator hoses collapse a little bit. Maybe make themunusualy easy to squeeze or something.

Re: Overflowing antifreeze reservoir
 

I would say I have used two quarts of Honda premix in 100K. So it's not much. I am going to have to monitor my cars. I have alway assumed that they start cold completely full and of course top out at around 200+ degree to release the thermostat. At that point, all three of my cars seem to hold a set spot on the temperature gage no mater what. I remember my old 85 Civic going up on big mountain runs but it had a 3 speed automatic and ran at 4K going down the interstate. I had always assumed the hose expanded and what not. Sure you have see it. I just did not realize that the cap would seep until 20lbs and I would have thought the fluid coming thru would instantly boil. My CRV is so well engineered and designed, I rarely ever see the fans come on.

Re: Overflowing antifreeze reservoir
 

The temperature gauge is heavily buffered in newer cars, too many people freak out over normal operation of real gauges because they don't understand anything about their appliance.

The needle might stay in the middle of the dial, yet actual temp might vary by 50*F or more.

Cap relief pressure is usually 13-15 PSI. Operating temp is usually kept well below boiling, so....

Re: Overflowing antifreeze reservoir
 

agree,

if the needle starts going above the "normal" position in these cars its pretty god dang hot already, even before it gets anywhere near the red

Re: Overflowing antifreeze reservoir
 

I went and got the Honda thermostat and radiator cap Saturday. The reservoir was a little over the full mark. I filled the radiator which only took about a cup. And but the Honda radiator cap on. I'm waiting for the car to cool down to see if it helped. I did notice that the aftermarket radiator cap I had on it was deformed on the inner metal ring like it was warped. I'm waiting to put the thermostat in. I'll post my findings as I get them.

Thanks for all the help. I was going to do the shop air test today but got tied up working on another vehicle.

Re: Overflowing antifreeze reservoir
 

Hey brother I know it's been a long time sense u dealt with this issue UT did the new Honda thermostat and cap solve the problem?

Re: Overflowing antifreeze reservoir
 

Your head gasket is blownRead: https://www.civicforums.com/forums/3...reference.html