First post here...kinda long so bear with me.

I am comfortable working on cars but this one has me beat. I have a 98 S90 with a recurring coolant problem. The car right now has ~160k miles and I have maintained it exclusively for the past 4 years or so (wifes car and her dad took care of it before that.) It has never had any real issues until now.

The radiator cracked where the upper radiator hose connects so I replaced it about 8 months ago. Everything was fine for 1 week after that then, for those that know the S90 (or maybe other volvo's have this too, I don't know) the little plug in the top right corner of the radiator popped out while driving, shooting all of the coolant out. I checked for obstructions and found that the thermostat had broken up so I replaced that. Filled everything back up, put the plug back in and everything was good until last week (so about 7 months.) The new radiator developed a small leak. Then the plug popped out again and again I lost all coolant. I checked the thermostat again but it was fine. I replaced the radiator again since it had a crack and it has a lifetime warranty. Filled everything up, put that plug back in and all was well until yesterday when that damn plug popped out again.

It's like pressure is building up on one side and follows the path of least resistance blowing that plug out.

So, the system has been opened up twice for radiator replacements and the thermostat has been replaced once yet this stupid plug keeps popping out. Has anyone ever had this happen? What could cause pressure to build up like that? Is there any special procedure for "burping" the coolant system of air that I am missing? Could something like a failed water pump be causing a blockage?

Thanks

 

Those aftermarket radiators are a PITA in my opinion.
BUT you can wrap a wire tie through the fins on the radiator and around the tank holding the plug in.
That design is a very poor one due to the problem you are having I have seen it to many times to keep track of.

 

I did that after the first time the plug popped out. So the factory radiator does not have this plug? Is there another means for pressure relief? Could I epoxy it in there so that it never comes out?

 

Im not sure you are really building up that much pressure the plug doesn't really like to stay in there very much.
Did you install the plug totally dry?
It is not supposed to have anything at all on it when you put it in.
Did it break the wire tie?
Usually once the wiretie is on there it won't come out.
No the OEM rad. doesn't have a plug like that. That is for the earlier cars that have a sensor for the cooling fan.

 

Oh I see what you mean. I didn't do that. I assumed it needed to be able to come out if the pressure went up so I rigged it to where the plug would not be lost if it did pop out. I know I haven't been real observant of it being dry or not.

I will have to try the wire tie through the fins.

Thanks for the tip.

 

Let me know how it goes.

 

Well, so far so good.

I picked up a replacement plug and grommet from volvo and put that in. I then ran wire around the end tank to hold it in. We'll see if it pops out again.

The plug from volvo does seem to fit tighter than what came with the radiator.

 

Cool keep me updated.

 

That is so crazy. The exact same thing happened to me and my 98 S90. First the thermostat got stuck over heated the radiator and it broke. I fixed it with some quick steal, and it held for a few days untilthen the upper left plastic part of the radiator cracked pouring fluid all over the place. ( both times this happened in taco bell drive through) haha. I feel your pain buddy,I really do. Good luck with it all.