Air to liquid intercooler to get your winter MPG back

robnitro

Veteran Member
Joined
Jan 19, 2004
Location
NYC area, NY
TDI
2001 Jetta TDI GLS silver
We don't just have an exhaust pipe/cat/muffler past the exhaust valves, we also have a turbo which creates backpressure, but I didn't make that clear (fixed my post above).

I meant the backpressure of the exhaust manifold which does change based on the turbo vane position. EMP.
More boost request, vanes more closed than if low or no boost request...

Simplified formula, but work of the turbo is work= pressure X flow.
If you can reduce the pressure drop that the turbo uses to make boost, it is doing less work.
 
Last edited:

zovix

Member
Joined
Dec 19, 2006
Location
Sweden, Norrtälje
TDI
Audi A6 2,5TDI
Cold weather milage

Hi there

I live in Sweden and I believe that it's good for the engine to block off intercooler or even to preheat air to the engine in wintertime at moderate loads.

Why? Because the air and fuel temperature affects the diesel fuels time to ignite. When the injector opens you have a slightly delay before the diesel fumes ignite in the cylinder. If you shorten that delay timing is more accurate and engine gives more power, if the delay is to long the timing is late even if timing is on time due to what the ECU sees.

Scania a Swedish engine and truck manufacturer even has thermostat controller to it's coolant to air liquid intercooler. The thermostat sets intake air temperature to 48 deg celcius and preheats air when colder and cools it when hotter air is pushed from the turbos.

Why don't we see this in cars? Because it's more expensive and VW thinks that poor mileage in cold weather doesn't effect too many customers.

/Z
 

Mike_04GolfTDI

Top Post Dawg
Joined
Nov 19, 2003
Location
Richmond, BC, Canada
TDI
Mine: 2019 Golf R DSG, Wife's: 2015 Golf Comfortline TDI
I know this is an old thread, but anyway.... Regarding switching to an air-water intercooler with the goal of not intercooling in the winter, wouldn't it be a lot easier to just bypass the existing intercooler in the winter?

You know, make it so the air comes out of the turbo and goes to the intake directly? You'd need a charge pressure sensor in the pipe, because it is normally in the intercooler.

Anyway, that would be a simple way to test out whether not having an intercooler does any good.
 

foggedz

Well-known member
Joined
Aug 5, 2013
Location
Rockford, IL
TDI
2013 Jetta TDI
IMO the best thing for winter MPG's is to put a coolant heater on the car. Put it on a timer so that the heater runs for about 1hr prior to your trip.

The first 5-10 min of running a car that is not warmed up kills the most MPG for your trip. The MPG is so bad in the first few min that even after the car gets warmed up its difficult to offset those first few min unless you have trip time that is +45 min.

I have a 20 min drive to work. In the summer I average 45 mpg on that trip. In the winter with a coolant heater I average 43 mpg. If I forget to plug the heater in, I would be lucky to get 36 mpg.
 

zovix

Member
Joined
Dec 19, 2006
Location
Sweden, Norrtälje
TDI
Audi A6 2,5TDI
I know this is an old thread, but anyway.... Regarding switching to an air-water intercooler with the goal of not intercooling in the winter, wouldn't it be a lot easier to just bypass the existing intercooler in the winter?

You know, make it so the air comes out of the turbo and goes to the intake directly? You'd need a charge pressure sensor in the pipe, because it is normally in the intercooler.

Anyway, that would be a simple way to test out whether not having an intercooler does any good.
The thing is that the intercooler is doing good in low temperature but when in idle or light load it's cooling the air too much. Naturally it's no big money to save to retrofit a liquid to air intercooler just to gain some winter mpg. But if you combine it with other mods or want to increase your intercooling capacity any way the liquid to air intercooler could be worth looking in to. Especially if you often drive in cold climate.

/Z
 

zovix

Member
Joined
Dec 19, 2006
Location
Sweden, Norrtälje
TDI
Audi A6 2,5TDI
IMO the best thing for winter MPG's is to put a coolant heater on the car. Put it on a timer so that the heater runs for about 1hr prior to your trip.
The first 5-10 min of running a car that is not warmed up kills the most MPG for your trip. The MPG is so bad in the first few min that even after the car gets warmed up its difficult to offset those first few min unless you have trip time that is +45 min.
I have a 20 min drive to work. In the summer I average 45 mpg on that trip. In the winter with a coolant heater I average 43 mpg. If I forget to plug the heater in, I would be lucky to get 36 mpg.
In Sweden almost all cars have coolant or block preheater installed. Up in the north when temperatures fall to -30 deg. C a Diesel engine have a big difficulty starting with out.

Down here in the Stockholm region temperatures seldom drops below -20 deg C.

/Z
 

turbocharged798

Veteran Member
Joined
May 21, 2009
Location
Ellenville, NY
TDI
99.5 black ALH Jetta;09 Gasser Jetta
IMO the best thing for winter MPG's is to put a coolant heater on the car. Put it on a timer so that the heater runs for about 1hr prior to your trip.

The first 5-10 min of running a car that is not warmed up kills the most MPG for your trip. The MPG is so bad in the first few min that even after the car gets warmed up its difficult to offset those first few min unless you have trip time that is +45 min.

I have a 20 min drive to work. In the summer I average 45 mpg on that trip. In the winter with a coolant heater I average 43 mpg. If I forget to plug the heater in, I would be lucky to get 36 mpg.
This is not the case on older TDIs with no DPF. VW did that to help get the DPF up to temp quicker.
 
Top