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TDI Power Enhancements Discussions about increasing the power of your TDI engine. i.e. chips, injectors, powerboxes, clutches, etc. Handling, suspensions, wheels, type discussion should be put into the "Upgrades (non TDI Engine related)" forum. Non TDI vehicle related postings will be moved or removed. Please note the Performance Disclaimer.

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Old January 27th, 2019, 17:47   #1
Yourbuddysatin
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Default 2012 CR Jetta overheating

Hey guys,

Iíve been tinkering with a 2012 Jetta tdi. It has an overheating problem but I have not a clue why. Blows nice hot air so I doubt the t stat is stuck. Changed the water pump and all that so I know thatís ok. Upper rad hose gets hot and lower is cool. Fans come on. No pressure in the system from what I can tell and never boils over in the expansion tank. I changed the temp sensor just to see if that would be it and its still getting hot. It will go up to 100c at idle and climbs over 122c(coolant light comes on) and rising when driving. My next step is to pressure test the coolant system. Anyone else run into a similar problem?
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Old January 28th, 2019, 04:02   #2
GreenLantern_TDI
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No pressure in the system sounds like air. The water pump cant build pressure or circulate coolant pumping air.
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Old January 28th, 2019, 04:17   #3
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Sorry I meant it’s not over pressure. It bleeds pressure off when i unscrew the cap.
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Old January 28th, 2019, 05:27   #4
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The thermostat has nothing to do with the heater. Although it is rare, I'd replace the thermostat first. Which, I have bad news for you, is a time consuming process. I'd also get the plastic pipe that likes to break, and the oil filter stand gasket.

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Old January 28th, 2019, 06:04   #5
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Oh Christ full front end removal?? Just my luck. So if the t stat isn’t opening I’ll still get heat?
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Old January 28th, 2019, 06:55   #6
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Coolant is ALWAYS flowing through the heater core, regardless of what the thermostat is doing. Thermostat controls the flow of coolant through the radiator.

You can just pull the lock carrier assembly into service position, you do not have to take it all the way off, I just do it that way because it is easier.

The plastic tube requires you to remove the oil filter stand, as it is attached underneath and wraps around to the bellhousing area.
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Old January 28th, 2019, 07:42   #7
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Thanks oilhammer. I appreciate the info. I think I will pressure check the system make sure there is not a leak anywhere then aim to change the thermostat.
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Old February 1st, 2019, 05:11   #8
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Having radiator hose hot on one side and cold on the other should have been the red flag for you.
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Old February 3rd, 2019, 09:51   #9
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From experience the stats on vag group cars get stuck allways in the open position so they over cool the engine. I would say a blown head gasket but i would put a new stat and bleed the system just in case!
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Old February 3rd, 2019, 09:58   #10
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Could also be a blocked up radiator.
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Old February 3rd, 2019, 13:52   #11
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It’s torn down now and waiting for parts to come in. Rad is good I checked it and I did a leak down test and it passed with flying colors. I have to say the thermostat is the problem. I will know by the end of the week for sure.
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Old February 8th, 2019, 19:37   #12
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All fixed up. New thermostat did the trick. Probably had about 5 hours into the whole deal. No temps over 90c.
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Old February 9th, 2019, 13:33   #13
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Great! Thanks for reporting back.
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Old February 9th, 2019, 18:32   #14
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With regards to tsat failure - does this tend to be a function of time vs mileage vs runtime?
For example, a car driven 10kmi/yr will have 12yr between tbelt service and therefore have a 12yo tstat.
But someone that drives 20kmi/yr will have 6yr between tbelt service, therefore the tstat will only be 6yo...
Would this make it less likely for one to see a tstat fail “out of turn” since its being replaced at a younger age (as a function of time) even though it’s seeing more mileage/runtime?
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Old February 9th, 2019, 18:57   #15
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I personally don’t believe it’s a very common problem. A friend buys a lot of these mk6 tdis and this is the first we ran into with a overheating problem. This car is pre emmsions fix also so I think this one was abused.
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