stew32

I've noticed the water temp readout on my Scangauge will drop by a couple degrees about every 5-10 seconds when I'm sitting at a red light, have the heat on, and the outside temp is below freezing. It's really weird- I've never had a car do this before. I've also never had a car with such a small engine so I guess this is normal? Temp will drop faster when it's below the normal operating temp (~182+ degree F) but it'll still drop after it's fully warmed up. One day when I'm cold and bored I'll see if I can make the blue dash light turn back on. My first winter with the xB has been a big change from my SUV which would warm up almost instantaneously (while getting 13 MPG)...

PakanaHerruus

not exactly sure what your saying.. but having the heater on does help keep heat from the motor.. the heatercore is like a second mini radiator. so its not as rare as you may think it is.. thats why they say when your vehicle is overheating.. to blast the heater..

Max

There have been several days lately where I could not get mine up to 182, no matter how long or fast I drove.

stew32

Ok, I guess I just never had a vehicle heater that could make the engine temp drop so fast. I don't recall the water temp in my other vehicles with 2+ liter engines dropping noticeably while sitting at a stop light.

It seems to do ok if the temp is in the mid 30's or higher. The last few days it's been in the 10's and 20's and I've got no heat for most of my commute. If I sit there and idle, it doesn't warm up fast. If I drive, I'm almost at work by the time I can turn on the fan and get any heat (~150+).

PakanaHerruus

ooh, now i see what your saying.. i thought you meant for your vehicle heat.. not the heat coming from the heater.. what i do is just blast the heat with the defrosters on.. when it warms up i switch it to heater..it does really get that cold here.. (California) but somenites it can take a while to get going..

stew32

Ok, that could work. Defrost makes the A/C compressor run- heat coming off the condenser in front of the radiator plus extra load on the engine and higher idle from running the compressor could make it warm up faster?

XbbbbBox

Here is a little info - I am not an expert on engines - but I do have a lot of technical experience with heating hydronic boilers and coils - here is what is happeninig.
The low water "mass" of the engine - combined w/the low output of the rpms at the light is causing the drop. Remember the heat is a byproduct of the combustion process. Because you do not have a great amount of mass- large water volume- not many Btus are stored. Also when you run your second radiator - the heater coil(which is just a heat exchanger- along with your radiatior which is in the cold)- you are pulling Btus from the engine water - thus lowering the water temp. The little water that the heater coil holds counts for a lot - especially since you have a low mass engine to begin with.
I do not know how much water these engines hold - but I am sure it is minimal - especially compared to larger engines.
I have a remote start to warm my XB.-I can tell you when idling in the real cold it takes a long while for the temp to increase - also uses a lot more fuel than I would have ever guessed!
When under load - many more btu's being produced- our little engines have to work hard, thus plenty of heat as a byproduct.
At the light the temp will continue to drop - at some point the temp will stay constant.
You should never see the blue light come on - though theoretically I suppose it is possible if it was cold enough - like say on Pluto. This is why you may have seen some big diesel trucks with a cover over their radiator - to get the temp up by blocking heat exchange from the radiator in the real cold!
Hope this helps.

365Motorwerks

Sounds too cold for me to be outside I know dam us cali folks!
You think your radiator fan is kicking on and dropping the temp?

dgHotLava

not the fan...it is the thermostat opening and closing...
the fan will come on when the t-stat is open and the temp will not drop.

when at the light (stoped) the motor will get warmer and the t-stat will open.
this causes the anit-freeze to be diverted to the radiator...the fluid in the rad is then forced into the motor.

the fluid from the rad is cold and when it reaches the engine will reduce the temp fairly quickly...

this is normal.

365Motorwerks

Good call!
And Happy B-Day!