Coolant Leak From Temp Sensor on Lower Radiator Hose

[VaTechZHP]

I have just complete an overhaul of the cooling system and while driving around, I found I was leaking a substantial amount of fluid from the temp sensor.

I know there is a gasket on the sensor, that was reused, but I guess could go bad? I am able to turn the sensor in the housing slighly back and forth as well as wiggle it up and down slightly. Is there supposed to be any play in the sensor at all? Certainly doesn't seem water tight especially if the car is being driven.

Any thoughts?

[kayger12]

Definitely sounds like a bad o-ring. I believe DW knows where to pick up the proper size o-ring.

[VaTechZHP]

Keith,

Thanks for the reply. In messing around with the system, and just walking inside, I would assume a considerable amount of air would now have gotten into the system? I was trying to see if the system would bleed properly and all I got was a really odd surging of water/coolant mix that would come out of the expansion tank. I had not seen something like that before, but it could just be large pockets of air escaping out of the system?

I also noticed that the upper radiator hose was very hot to the touch, which leads me to think the thermostat, which is also new, is working properly, but the lower hose was outside temperature and did not seem to heat up at all.

Could all of these be related to a leak in the system and lots of air in the system as well?

[aurelius]

I am about to do the cooling rehab on a friend's 325i and am on the verge of ordering the parts.

Did the new temp sensor/fan switch not come with a new o-ring?

[VaTechZHP]

I did not get a new sensor with the kit. I am picking one up today and hoping it has a new gasket.

[kayger12]

Air pockets can definitely wreak all kinds of havoc with the cooling system.

I'm thinking a new sensor, o-ring, and good bleeding will have you good to go.

[VaTechZHP]

I put the new sensor and O-Ring in and it seems to be functioning just fine so far. I bled the system for some time and drove it around the neighborhood. Everything is dry in the compartment and I was getting some very hot heat. I'm going to drive it some more tonight for more than 5 minutes and see how it goes and refill as necessary.

Thanks for the help!

[LivesNearCostco]

From my experience with an aftermarket thermostat sticking shut, one of the hoses does not heat up until the thermostat opens, which is somewhere between 90C to 97C as measured by the main coolant temp sensor in the head (not the one in the radiator hose). I think the lower hose stays cold until then because it leads to the radiator.


I also noticed that the upper radiator hose was very hot to the touch, which leads me to think the thermostat, which is also new, is working properly, but the lower hose was outside temperature and did not seem to heat up at all.

[danewilson77]

Great job VaTechnoStud.

[kayger12]

I put the new sensor and O-Ring in and it seems to be functioning just fine so far. I bled the system for some time and drove it around the neighborhood. Everything is dry in the compartment and I was getting some very hot heat. I'm going to drive it some more tonight for more than 5 minutes and see how it goes and refill as necessary.

Thanks for the help!

Nice work. Sounds like you're good to go. :roundel

[VaTechZHP]

Put ~250 miles on it yesterday driving to Rockville MD and back, ran like a champ! Now to just get the AC belt back on the car and the undertray reinstalled and it should be good to go until I decide to tackle the CCV...

Thanks for the help everyone!