So this problem I just noticed has me baffled. I noticed the coolant tank was low, near empty one day and filled it withing the limits. Then after a few days of driving I checked again and my engine looked like it has been sprayed by coolant ( had all these white dry water/coolant marks everywhere) and the coolant overflow tank was near empty again. I did this 2 more times and same thing.

Then the last time I filled my overflow tank to within the limits, cleaned the engine to see if this problem returned. Now the engine doesn't look like it has been sprayed by coolant anymore but today when I checked the overflow tank was low again.

What could be causing this problem? There are no visible bubbles in the radiator while the engine is idling, the compression is 225 across all 3 cylinders by the firewall and 230,225,235 across the front ones. The difference between the highest and lowest comp. numbers is less than 5%, which is well within the tolerance limits. The oil clean and not milky, doesn't look like it's getting water/coolant in it. These observations would lead me to rule out a head gasket issue, but for some reason, I still think it could be the headgasket since the coolant has to be going somewhere now since it's not being sprayed on the engine anymore... Any help is greatly appreciated. Thanks for reading

 

I had the elbow on my overflow tank crack where the small hose that leads from radiator to overflow which caused fluid to leak.

 

I would check the radiator cap first and any leaks between the radiator cap and the overflow tank. If the cap is venting into the overflow below the rated pressure and especially if it's basically wide open to the overflow which it sounds like it is, you will have excessive water being pushed into the overflow when it gets hot and then it tries to suck it all back into the pressure side of the cooling system when it cools.

It will also let the coolant boil at a lower temp and since there are parts that run above the boiling point of water and water temps normally run right around boiling, without pressure on the system you might run into boiling. Once it boils it stops cooling completely.

 

Thanks for the reply's guys. The cap looks fine to me, how do I make sure it's sealing right?

 

Did you check the plastic cap of the overflow tank too?

Mine was cracked pretty badly

 

Mine isn't cracked but it seems if I tighten it too much it will get loose again, but I can get it pretty tight. Thought this was normal.

Just checked the car again as its cold as sat over night, it seems the coolant is not back within the limits (though a bit lower than when I filled it). So when its hot coolant is being sucked out and when the car cools, coolant is coming back in. Should I replace the overflow tank and cap?

 

Should be the opposite. When hot there is "expansion" of coolant and it should rise in the overflow. When car cools and the coolant "shrinks" the reservoir should go down as coolant is sucked into the radiator. The overflow res cap's ability to be tightened itself should make little difference as the coolant flows through the little rubber tube so unless there's a crack where the tubes hook up I don't see an issue. The terms "expansion" and "shrinks" are used very loosely here.

Is it possible the radiator cap itself is bad? If so I'd still think you'd see signs of coolant dripping around the reservoir. If it is bad I'd think you'd exceed the overflow reservoir's capacity and then when the car cools you'd end up on the low side as it's sucked back into the radiator.

 

Usually when the cap is bad it does exactly what he's experiencing. You get a much larger than normal volume of water being transferred between the radiator and overflow tank from cold to hot and back again. It can lose the ability to hold radiator pressure yet still not leak externally. It has a seperate seal for that. It's technically "leaking" at too low of a pressure into the overflow.

I suggest doing the cap sooner rather than later because if the system isn't building pressure, you can run into other more serious problems. When the engine is hot, squeeze the upper radiator hose (using a rag or something so you don't get burned). It should be pressured up and hard. If it's not, it's for sure the cap. Even if it is hard, it can still be the cap opening too soon.

 

Yes sorry, wrote it out wrong. Expands when hot, shrinks when cold.

Thanks, I will do the cap this weekend. Now that you mention it, I noticed the upper hose is softer than I'm used to seeing it on my previous hondas...

 

Thanks again, it was the cap. When I bought the new one and compared it to my old cap, I noticed that the small bottom rubber piece was missing, and this caused my issues. Now that I replaced the cap, the upper hose is hard once the car is warmed up not like before. Also the fans cycle on and off a lot less.

Pic is of my old cap, shows the bottom rubber seal missing (you can see right through the cap)

 

Good to know and thanks for the follow up. All to often we get a question and then we all give our suggestions only never to hear back. So it's good to see the feedback as it increases the helpfulness to members in the future. (Assuming they search )

 

That's good. I don't think the missing piece can go anywhere so I doubt any harm would be done.

Now you have a larger volume of water in the system when hot and I guarantee there was localized boiling since it essentially had zero pressure on it. Even though the temp on the gauge will stay he same, the hot spots in the engine like the heads around the exhaust valves will actually be running cooler since it can't boil now.