Thermostat or Radiator what a dilemma

I posted this in the engines section so maybe that was wrong of me. Hopefully this is the right place.

2003 Mazdaspeed Protege 100k miles
Recently I am having an issue with my coolant steaming out. It does not steam out of my reservoir. The engine never gets overheated the temp gauge is always steady at about halfway or bit under. it will only steam after I am down the road a ways but it does not steam every time in fact it has only done it 3 times in three weeks. The last time it steamed it was on my short drive to work which it was a bit cold that morning about 35F. I filled it back with the inch that was steamed out of my bucket and went to lunch, no issues. Went to go home and it started to steam on the ride home. Stopped to make a pickup and it steamed at take off but it stopped somewhere on the ride home because it didnt do it when I pulled in at home. That was all city driving I cant seem to get it to do it when I am on my hour commute on the highway, of course I wouldnt see it then but I am not dropping fluid either. When it does steam out it gets fluid all over the pan at the bottom and a few places up top but I think it is being blown up high. There is no mess arround my Reservoir. it gets on the engive of course and you can tell by the smell. the car leaves no puddles when left in the garage, overnight or several days.

I first took it to pepboys they said new radiator it failed the pressure test but I hear that losing a few pounds per over time is normal.

I took it to a radiator shop that put it under pressure and looked all over for leaks and could not find anything they had it under pressure all morning.They told me about the pressure test gradually losing pressure as just being normal.
They said I dont need a new radiator it doesnt seem to leak.

I then took it to the Mazda dealership. They are also now telling me I need a new radiator it was again losing a few pounds of pressure over 30 or 40 mins I would guess. When I took it to them it had some residue left on it from the radiator they put it up and showed me where they think it is coming from. on the bottom of the radiator there is the plastic pan that is crimped on to the aluminum part of the radiator they say that it is leaking out of that crimp. They say that it may only leak at say 68 degrees and after it gets hotter than that then the seal inside expands and fills the gap thus stopping the leak. One would think that it would do it everytime then in some form or fashion but it doesnt I can wash off the engine and go for a week and nothing happens and the bucket level doesnt drop and no residue. When we first took it into the dealership we though that it was going to be a thermostat but the tech doesnt seem to think it is that. He states it would happen more often and would come out the bucket or if it was stuck open, the car would never heat up.So if it was a bad thermostat do you think it would steam out other places instead. I mean if it was stuck closed wouldnt it then come out the seal or wherever. When it does steam I can see the steam coming from the Radiator cap, and the hose coming out of the plastic top right by the Rad cap. Additional steam comes from whatever else the fluid got on also. I have seen it only steam from just the radcap and hose fitting and just for a bit, but then other times it is all coming out everywhere.

So the main things are that it never comes out the reservoir, it never gets hot even when it is steaming the car thinks the temp is fine, and it doesnt do it every time, it has only begun this when it started to get a bit cooler. So my dilemma is that I dont know if I should throw a new radiator in there for $500 or put a thermostat first which is much cheaper. The thermostat on this car has been replaced one other time before about 2 years ago, I think it was boiling out of the bucket though when that went.

What do you guys think? Thanks for your replies.
 
So when it 'steams out' where is it coming from? the radiator cap?
is there visible leakage anytime?
a leaking radiator would not cause your coolant to overflow from anywhere it would just, well, leak.
if you are running hot at times and having coolant loss at the same time from overhead my guess would be thermostat, it may be stuck closed. thermostats can get stuck closed and open, open would cause a long time to warm up, and closed would cause what i think you are describing above.
thermostats are cheep, you have 100k on your car. just change it and see what happens, couldnt hurt.
 
When it steams I have seen steam from the rad cap and from the hose on top right next to the rad cap. Steam also seems to come from down low on the radiator presumably from coolant spraying on hot stuff. One time it did steam only from the rad cap and hose on top just a bit and no coolant was seen anywhere else.
There is never any visible leakage I can see coolant but mazdas theory is that there is a gasket between where the alum and plastic bottom pan meet and that only at a certain temperature will it leak because being cold it is small and then when it gets fully warmed up the seal expands and fills where it is leaking. stopping the leak. it never puddles anywhere. the temperature gauge runs like it always has. right about middle. I am going to test the heater tonight and make sure that it gets fully hot I am told that will tell me something about the thermo but I think that it does get warm as it always has. I am thinking that I may change the Rad Cap for a highpressure one but if I have failed cap wouldnt it fail more frequently not twice in 3 weeks? thanks for your reply.
 
here's my issue with the radioator theory. If it's leaking thats fine, it's just going to leak, it will not cause leakage anywhere other than at that gasket. That should not cause any steaming around the radiator cap. as for my experience with radior caps, either they are good or they arent. and usually if they arent then you will see a visible tear in the sealing gasket or the spring is broken or super gummed up.
 
I think your problem is simply the radiator cap! if there is steam coming from the radiator cap that means the rubber gaskets are not sealing like they should! replace the radiator cap with a STOCK reguirement pressure radiator cap and you should be good.

with the thermostat, when it fails it will either be stuck open or closed! open will cause the car to take a long time to warm up and when you are driving in cold weather at freeway speed the temp will drop and you will not have heat from your heater. If it is stuck closed then your car will warm up normal but it will eventually overheat because the thermostat will not allow coolent to circulat through the radiator.
a way to check is to take the radiator cap off when the car is 100% cooled down and after the cap has been removed start the car, at idle look at the coolent in the radiator if it is circulating right away then your thermostat is stuck open, If it is not circulating then wait for the engine to warm up and then you should notice the coolent should start to circulate through the radiator, if this does not happen then your thermostat is stuck closed.
 
Go to the auto parts store and try an $8 rad cap. If that doesn't fix it, I'd replace the rad.
 
thanks for all of your replies the thing is that there is just steam coming from the radiator cap and the hose fitting so where is all of this coolant that gets on the bottom of the radiatr and the bottom of the pan come from?
I did check the heater last night as we had a bit of freezing rain and it warmed up find and defrosted the windshield so I think it is running at normal temp not at just warm.
So on the thermostat tests I thought that starting the car with the Rad cap off was bad bad? Also from what you are telling me if it is stuck closed then eventually it will overheat now that being said will the overheating show on the temp guage? I think that it would. Furthermore from what I have been reading if my thermostat was bad then the temp gauge would be doing crazy stuff correct? I plan on ordering a STOCK rad cap just to see probably get it from the dealer. I went to corksport last night and I was going to get one there but when you order online and are supposed to specify your trans it does not give you the chance to so I didnt want to get the wrong one. Are there any online retailers that sell the stock cap for sure? Thanks for your help!
 
Well just to update I ended up replacing the radiator I drove the car pretty hard on the way to pickup the radiator cap and it was steaming when I got to the dealership so I had the tech take a look I could tell it was coming from down low. he said it was definitely the Radiator.
So I replaced the Radiator. But now of course once they got that installed they said i should put in a new thermostat also because the fan kicks on to early meaning that the engine is running a bit to hot even though the dash gauge looks normal. So i dont know what to make of that, I also asked if that could have caused the first radiator to go bad but I didnt get much of an answer. I guess i will put a thermostat in also in a few weeks since it is only about $100 to put in. The Radiator for this car is $410 by the way.
 
thats good that you got it fixed! i would say wait alittle before you change the thermostat, because it either wont work or it will! i have never herd of the thermostat cuasing any kinda of leakage from the radiator, your old radiator probably got a hole from FOD on the road!
 
The fans always kick on to early, I would barely start my car after it was warmed up and the fans would be cycling.
 
thats good that you got it fixed! i would say wait alittle before you change the thermostat, because it either wont work or it will! i have never herd of the thermostat cuasing any kinda of leakage from the radiator, your old radiator probably got a hole from FOD on the road!

Actually an update on this was that the seal they use to connect the aluminum part to the plastic bottom pan was the problem at the crimp. Seems it would only leak at certain temps though I replaced the radiator and all is well.
 

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