My heat isn't working and I'm pretty sure I need to flush my heater core. I'm not 100% sure though, I feel as if maybe my thermostat is stuck open. When I'm driving on the highway for long periods of time my engine will cool down to 1/4 of the temperature gauge. Granted, I do have a cold air intake (which I have no idea if it would work to such a degree to cool the engine down that much, please correct me if I'm wrong). It was already installed when I bought the car so I don't know if it did it prior to install. The car heats up no problem to full operating temperature and doesn't exceed the half mark on the temperature gauge, which is why I'm not sure if it's my thermostat or not. I'm going to flush my heater core regardless, I just want to know if it's normal for my engine to be that cool after highway miles even if I do have a cold air intake; and if not, is it my thermostat?

 

I think its your thermostat not closing.
If it's warming up to half way then its opening OK, but sounds like its not closing. These are electric not the old thermal ones, so the are driven from a second temperature sensor in the water pipe next to the radiator.

 

Thanks for the info! I checked my coolant today and its was brown and had rust on the bottom of the reservoir cap. How do I go about getting all of the rust out the system? By the way, why is there rust in there to begin with? On my c5 2.8 this happened and it was due to a failing water pump.

 

I had a similar problem with a 2005 1.8T. When my son purchased it we found the coolant was very rusty brown. I flushed it multiple times, used a radiator flush then multiple water changes. There's a post somewhere on this site of a member who flushed the system something like 9 times (maybe the allroad section!).
On the 1.8T there's a metal coolant line that runs across the top of the inlet manifold and I found that had rusted and, the water pump failed soon after.
The fact yours actually gets cold not overheating sort of goes against a water pump problem.
One test I found if you want to try something at no cost. On the heater hose to/from the interior heater coil is a white circle just as it comes through the fire wall to the engine bay just near the clamp. If you loosen the clamp, slide the heater hose part way off, there is a bleed hole in the circle. Reclamp leaving the hole exposed then if you then start the cold engine, you should not get any water coming out the bleed hole as the thermostat should be closed until the engine warms up. As the engine warms up, the thermostat should open after a few minutes (depending on your climate), you should get a small fountain (say 3-4 inch) squirt of warm coolant out of the bleed hole you exposed. If you get the squirt even when the engine is cold, your thermostat is not closing, if you get a trickle of warm water but no pressure, then the pump is not pressurising enough. I'm not a mechanic so if someone else has a better no cost home test jump in.

 

That's very accurate, and yeah most likely the thermostat isn't closing as his temp. drops on the highway. I don't know what engine you have, but on a 1.8T Passat I once had, there was an o-ring at the oil cooler (between the oil filter and the engine), and this o-ring was leaking and mixing the coolant with oil. Also the oil cooler could be broken inside and do the same thing. Good thing is that because coolant is a lot thinner than oil and due to pressure differences, if the oil cooler is the culprit it would only mix one way, so oil would get into your coolant not the other way around, which saves your engine, but definitively I'd investigate oil cooler or even head gasket, oil and coolant is not a good mix, so if you want to keep your car, it's something I would look at right away.

Good luck,

 

Wow very informative! Thanks a lot!

 

Thanks a lot I'll be sure to investigate!