If there is ANYBODY out there with a 98 Civic whateverX right now, would you PLEASE go look at your coolant reservoir and tell me if the valve on the top, where the hose goes, is FIXED or LOOSE? I swear I have the wrong cap on mine which is not allowing the coolant to go back into the radiator, and after about a zillion google searches I can't find the answer. Would be greatly appreciated! Free bowling if you live in the Seattle area! Possible cookies!

 

96-00, all same in this regard.

I don't believe there is actually a valve in the coolant reservoir cap. I think it's just an L joint. The coolant system is closed so when there is too much pressure, it overflows into the reservoir. When the pressure is low, it sucks some back up. I don't believe that there's a valve that does this. Just pure radiator pressure.


Does your coolant reservoir look like mine?

 

Yes it does! But the aftermarket one that the husband bought (for 30 FREAKING BUCKS I might add) has the L-joint LOOSE. It looks like it has a spot for an O-ring but it didn't come with one, or new hoses either. I think this is keeping the coolant from going back into the radiator--i.e., no pressure due to air leak, so no sucking the coolant back in. Mechanic did a MacGyver bushing (using part of the reservoir hose, it's long enough) and today it didn't overheat. I just got home from a long drive and the reservoir didn't bubble over, it's a little high but I marked where the coolant is and will go back out in a few hours to see if it's gone down. He also turned off the P0420 code with the COOLEST OBDII scanner I have ever seen (looks like an IPhone, wireless and everything) and it hasnt yet come back on. Next project is the fuel filter, with new plugs and wires it's not keeping up. Although that looks easy compared to the hell I went through with the radiator (forgot to buy new hose clamps, took me and my trusty vise grips forever to get them off). Thanks for your reply!

 

And if you ever come out to Seattle, I WILL hook you up with free bowling--part time bartender at a bowling alley. Just PM me!!

 

OH, I see now. Loose or tight, shouldn't matter as long as the hose is submerged in the coolant. There can be air in the reservoir, moving in and out as freely as the coolant. But fluid dynamics and gas dynamics are different.

All things considered with the fluid pressure, as long as there is an airtight seal from hose to L joint to hose to radiator, and the radiator has an airtight seal (properly bled, filled to capacity, etc), AND as long as the hose is submerged into the fluid in the reservoir, the system should function properly.

heh, I've never been further west than Denver. But I used to work at a bowling alley.

 

Okay but what still stumps me is that the original reservoir had the L-joint STUCK (can't think of a better word) in the cap--didn't have an air leak. There was NO air, gas, fairy dust, whatever, getting in OR out of the cap. Driving me nuts. It is NOT the head gasket (a mantra I keep repeating) so it's got to be something else. Going to change out the radiator cap tomorrow too (payday friday!! Time to buy new parts for the car!!!) And I still have an hour before I go out and check the damn reservoir again. JUST ONCE THIS WEEK I want to NOT have to work on the car when I get home.

 

There probably WAS air getting in and out through the cap, but it was around the threads, not the cap itself. If the reservoir was meant to be air tight and pressurized, it would have come with a rubber seal. Mine doesn't have one and I don't overheat. So as long as the fluid is between the min and max lines, you should be good.

 

The reservoir cap should fit loosely. Air needs to go in and out as the level rises and falls. But the hose system must be airtight from the bottom of the reservoir to the radiator neck.

 

Well, after driving in this morning the reservoir didn't overflow, level is the same as it was when I left home (23+mile commute). No overheat. Next suspect is the radiator cap--the new rad came with a new cap, but it's possible it could be crappy. What's 8 bucks? And can you guys recommend a good fuel system treatment? Going to change out the fuel filter tonight and have the fill the car up--want to throw some cleaner in when I do it. Any opinions appreciated!

 

Lucas injector cleaner is pretty good. It runs through the system.