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Old 01-08-2013, 10:41 AM   #9
OEM ///Member
Join Date: Nov 2009
Location: Fairfax, VA USA
Posts: 22,837
My Ride: 330CiC, M5, X5, E93
Another side effect I have noticed about engines that tend to run too cold seems to be more carbon build up in the intake ports and on the back of the intake valves, leading to more cold start stalls, usually the first start of the morning.

I had this problem with my daughters 20 Valve 4 cylinder turbo VW, yea you read that correct 3 (three) intake valves!! The stat was bad for a while in her car and it had no gauge and no way to read the temp without a scan tool that could read real time data.

Replaced the thermostat in her car, was only running about 180, put the 185 stat in the car, BANG, 200-205F rock solid (again temp sensor is in the rear of the cylinder head). Then ran a number (4-5) of Techron treatments back to back (Costco had a 6 pack on sale for about $18, probably should have bought way more!!) after replacing the thermostat and low and behold the car has no more cold start stalling on the first start of the morning.

It is crazy how many in the VW forums have a temp code and the first thing the want to do is replace the temp sender. It is cheaper and easier than the thermostat, but it is a WAY FALSE theory based upon what I have been seeing in a lot of cars across the board. I do not trust any thermostat over 2 years old anymore, anything over 4 years, I almost always just replace it. I now carefully look at coolant temperatures with my scan tools, BUT the problem is without a baseline from a sample of cars, how do you know what the proper temperature should be??

I am finding that on almost all but the BMW M series cars, it seems 200-205F is a pretty typical range not during the heat of the summer. Again the engine design and where the temperature sender is located factors into what the "proper and normal" operation temperature should be.
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