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View Full Version : Bad cats causing engine over-heating?



dantheman762
01-19-2010, 03:22 PM
Hey guys - Does anyone know if bad (plugged-up) cats can cause engine over-heating? My car has never had the temp gauge go past the center, even in the hottest days during the summer. Yesterday though (right around freezing - 32F), on the highway, it kept climbing. I cranked the cabin heat to help get rid of some heat and this helped, but I couldn't last that long with it so hot in the cabin. I stopped and popped the hood and everything is fine with the coolant level, serpintine belt and fan and no other obvious issues. I don't have a VAG-Com, so I don't know of any new codes.

To me, it would make sense that now, if both cats are gone (I read somewhere that they get "plugged-up" after time), then this would restrict exhaust flow. The engine did seem a bit down on power, but it might have been the placebo effect.

Thanks guys for any thoughts any of you may have on this.

dcampana
01-19-2010, 03:25 PM
so assuming you are getting the coolant to circulate (since the heat is drying your eyes from the HOT HOT heater):) it may just be a faulty CTS (coolant temp sensor). or maybe a fan switch?

those would be two thoughts i have.

dantheman762
01-19-2010, 03:29 PM
so assuming you are getting the coolant to circulate (since the heat is drying your eyes from the HOT HOT heater):) it may just be a faulty CTS (coolant temp sensor). or maybe a fan switch?

those would be two thoughts i have.

Thanks Dcampana - looks like I'll have to pick up a Ross-Tech cable. In the meanwhile, I guess I can use a multi-meter on those two components. Thanks again.

b4a41point8t
01-19-2010, 03:37 PM
Prolly cts. Think about it, if the car ran fine, no hissing or bubbling coolant, or smell of overheating, then chances are it wasn't over heating but rather just thinking it was overheating. Bad coolant temp sensor is my guess. Start with that. Takes 2 minutes to replace and should be changed anyway.

walky_talky20
01-19-2010, 06:16 PM
Yeah, change out the CTS for good measure. If it still gets too hot it is probably the impeller on the water pump that has failed. The original Audi ones are plastic and are a known failure item. I know that is the case for the 1.8T's and 30v's. I would think the 12v's might have the same issue, but I have to say I'm not positive.

dantheman762
01-19-2010, 08:11 PM
Okay, thanks guys. Yet another classic example of the amazing people on AZ helping out another Audi owner. Thanks to everyone for their replies!

P.S. Can the CTS be changed without draining the coolant? Not sure of it's location. Thanks.

dcampana
01-20-2010, 02:50 PM
you will have some spillage but not needed to change out. you will need to make sure you refill 50/50 with g12 and distilled water....

soundspeedstyle
01-20-2010, 07:21 PM
My cat is bad and sounds hella hot after I turn the car off. But my tstat is bad also so it runs cold. So idk but mine doesn't ever over heat