Cold Weather TDI Operation

In a recent post made in the Eastern Canada TDI Owners forum, I described how I partially cover my '03 Jetta's TDI engine water radiator with a piece of carpet when the present and the three to four day forecast temperatures are to remain at or below -15 Celsius (5 deg. Farenheit).

This proved quite useful during the January cold snap we had along the upper Eastern seaboard. Before using the carpet, I had no problems starting my '03 Jetta TDI wagon at -22 Celsius in the morning (using Shell's UltraDiesel) but it would take for ever for the engine to warm up and, to make matters more difficult, on long downhills, with the engine producing no power, the engine temperature would drop back from 90 to the far left side of the dial.

Opening up the centre grill in the front bumper to slide in a piece of carpet covering the lower 60% of the water radiator did solve the problem. Then engine temp remained bang on 90 even on long downhills and it did warm up faster after a cold early morning start.

My questions are: under unusually low winter temperatures, is it advisable to go as far as to plug up the inter-cooler air intake?

Also, what are the pifftalls, if any, of taking makeshift precautions to keep the engine warm during a sharp cold snap in the winter time?

Should the TDI engine's ECU nomally compensate for wide outside air temperature fluctuations? Could it be that on my car, the ECU was not doing its job properly before I inserted the blanket to cover the greater part of the water radiator?

I notice that recent models of pick-up truck sometimes wear a thermal cover on the front grill during cold winter days. Is that to say that TDIs should be operating with thermal covers as well, even though VW does not sell any as part of its OEM accessories?

Steve

E:

Nice country up there- my wife and I just vacationed in Bay St. Lawrence, Cape Breton last August for 6 days. Wasn't anywhere near long enough.

In answer to your question, many people in the colder climates do exactly what you describe. These little engines are extremely thermally efficient (like all diesels), so as a result unless they are under a bit of load they cool down because they don't generate a great deal of excess heat. With temps as cold as they are, it doesn't take much -15C coolant to bring the engine temp down. This coolant is coming from the radiator, which in the cold breeze will be at whatever the air temp is. By blocking part of the radiator from the wind, you allow the coolant in it to stay warmer, helping the engine maintain its temp.

VW engineers have to build their vehicles to run in Canada, or in Arizona, without a lot of physical difference between them (except of course, the fuel pickups). As a result, the tradeoff is a little bit cooler running in the cold. My Jetta took so long to warm up that after 3 winters of running around with my earmuffs on in the car, I bought a coolant heater so that I would have heat within a few minutes of leaving the house. Great little addition to a great little car!

Hope this helps...

-Rich

I don't think there is any advantage to be gained by covering the intercooler. The cooler the intake air the more efficient the engine will be. I realize that in theory there is a temperature where the air is so cold that it won't heat up enough under compression to ignite the fuel, but if you got to that point the car wouldn't be able to start. I don't know what that temperature is, but I doubt we would reach it in North America. (At least before the next ice age! /images/graemlins/rolleyes.gif)

Hmm, -22degC is about -8 degF. My coldest start on record here in New England is -7 degF, and she spends the night outdoors. Had to cycle the glow plugs twice to get her started ... after which she immediately roared to life. Let her idle for maybe 5 or 10 mins. Then drove her for 1-2 miles (2 or 3 km) and the needle for the temperature gage was coming up out of the low range. She was up to temp in another 3 miles or so. All back roads, mind you.

Now I read your post, and something sounds wrong. Putting carpet in front of the radiator should have no effect if your thermostat is functioning properly. There should be essentially no circulation in the radiator with the thermostat closed, so the carpet in front of the radiator with a functioning thermostat should do nothing. If the carpet is making the car warm up faster and hold temps, I think your thermostat is toast. /images/graemlins/eek.gif

Also a question ... is your EGR functional or disabled? Believe it or not, this makes a HUGE difference ... ask me how I know ... /images/graemlins/tongue.gif

E_Sepulchre, what you are seeing is normal.

Instead of carpet you might want to try some foam pipe insulation, very easy to add or remove in a minutes time.
Placing it over (or between) the center front grill below the bumper should be more than enough.
In the -40c weather we had here last week I didn't find a need to cover the intercooler area, the car heated up as long as I kept driving.

Steve

/images/graemlins/cool.gif

"Putting carpet in front of the radiator should have no effect if your thermostat is functioning properly. There should be essentially no circulation in the radiator with the thermostat closed, so the carpet in front of the radiator with a functioning thermostat should do nothing. If the carpet is making the car warm up faster and hold temps, I think your thermostat is toast."

Good point!! The thermostat issue had crossed my mind a while ago, then I forgot about it. In theory, you are right: the piece of carpet stuck against the water rad shouldn't make any difference and yet it did, as I said, especially on long downhills, by keeping the engine temp around the 90 mark. Yet, my Jetta TDI has only 20,000 or so miles on it. I doubt the thermostat would be defective.

I am starting to wonder if that piece of carpet simply had the effect of preventing less cold air from penetrating the engine compartment in general which would have allowed the engine block as a whole to stay warmer.

The Jetta owner's manual doesn't say much about cold weather operation, nor does it say much about fuel additives for use in areas where the quality of diesel at the pump is suspected to be inadequate for the environmental conditions.

Just as the FAQs point out, if your TDI is chip-tuned, the engine will be much more sensitive to diesel quality. I have experienced it and am still trying to find the right combination of top quality diesel and additive for cold weather operation.

Two points remain in my mind: why doesn't VW sell a winter bra as part of its accessories? The other point is that it would be nice, as a TDI owner, to get to know more about the design and behaviour of the ECU. I say this because it's been rumoured that this little computerized smart box can "learn" to adapt to various environmental conditions, varying levels of diesel quality, even the owner's driving habits, etc. If this is true, then, every time the engine runs a little rough or sounds a little noiser than usual, I can safely assume the the ECU will be doing its job of bringing the engine back to normal operation.

There are times when my TDI engine is as smooth and vibrationless as a 6-cylinder gas-powered new vehicle and other times when it sounds like a farm tractor. There are times when the low-end torque is readily available for zippy accelerations and other times when the engine must be coaxed a into the 3500 rpm + range to deliver adequate passing power.

In other words, engine behaviour varies with the weather, it seems, which at this time of year produces wild outside air temperature and humidity fluctuations.

So it's just perhaps a matter of going with the flow and accepting that the ECU is doing what it can, while one day my Jetta sounds and feels like a Cadillac and the next, like a farm tractor, depending on the weather change or quality of diesel supply from one gas station to another.

If there is a technical write-up somewhere on the net describing the design principles, capabilities and operation of the TDI's ECU, I'd sure like to know about it.

Blue skies,

Steve

A few weeks ago, I drove the 20 miles to work. My thermometer at home when I left read -34.2F. The car never did get above 180F. When I got to town, I turned the blower to #3 and the temp dropped to 1/2 normal operating temp. Was ok with coat on, etc.
How about this for an idea. Many of the big rigs up here in the north country rung louvers on the front of the grille and when it is super cold, they close them up to maintain operating temp and manually adjust to keep temp in the right spot.
Come up with a design to build these into the front of the car to keep temps up and have them operate electronically coinciding with the temp guage??? Do a group buy after extensive testing and we all become millionaires (just kidding)

I would love to be in on a project like this

I used to use a piece of cardboard covering the whole front of the radiator with a 1-2" slot running across the width of the radiator minus approx 1" both sides. Worked great, however, need to remember to remove w/warmer temps......

Some trucks did and some still do have the adjustable louvers for a front grill. I don't think VW engineers would make it manually adjustable on TDI engines for fear of misuse by VW owners, but automatically adjustable ones might keep the engine compartment warmer. Mind you, this would come at a price for the car buyer. Nevertheless, I wonder if VW ever considered offering front grill louvers as an option on TDI equipped VWs....

I see you have an EGR mod on your Jetta. Would you mind telling more about it? I read that one can keep the intake manifold cleaner by diverting return combustion gases away from the intake manifold, thereby prolonging the longevity of the engine. Is that what the EGR mod is all about or is there some other purpose?

Steve

You are mistaken. There is ALWAYS some coolant flow thru the radiator.

VW uses a "bypass" cooling system which maintains coolant flow thru the engine at all times. The LOW MOUNTED thermostat acts as a "mixing valve" by taking the 2 "inputs" (HOT from engine and COLD from radiator) and mixing them together to maintin the fluid temp going INTO the engine.

In very cold weather, the flow thru the radiator is sooo low that the "hang time" allows it to get OVERCOOLED.

I will not go into the physics of the bypass cooling system any deeper at this juncture... suffice to say that cutting the airflow to the front grille in very cold weather is not only GOOD for the engine, it will help the occupants get some heat too.

Just keep an eye on the temp gauge and if it starts to mingle in the upper range... turn the heat and fan on FULL and remove the cover from the grille. The temp will drop like a rock.

Personally, I use some lengths of slotted 1/2 inch foam pipe insulation on the grille louvers. I can remove/install any combonation I wish to "customize" the coverage. The color of the pipe-insulation matches my titanium Jetta perfectly.

I use 3" wide black tape on the front grille on my Insight. It works great. I plan taping off the lower grille on the Jetta, soon.

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I don't think there is any advantage to be gained by covering the intercooler.

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I have definetly seen an advantage in covering the intercooler. Three weeks ago I covered both the lower radiator grills and the intercooler grill with 1/2" foam pipe insulation. The car not only heats up faster ( about half the time it used to take), but I have seen an increase in my milage to almost summer levels. I don't think that all of the increase can just be attributed to a warmer engine, some of it must be due to a warmer charge getting to the engine.

That is an interesting conclusion.... but since you covered BOTH the grille and the intercooler intake, it has little basis for fact. Perhaps if you UNCOVER the intercooler intake and see if the MPG drops again?

I wonder if anyone has taken any IAT (IntakeAirTemperture) readings before/after the intercooler in sub-zero farenheit weather?

Can any one else who has covered one or both weigh in on this?

There is nothing like actual experimentation to solve the riddle of the covered intercooler grille, and I'll wait for empirical data from keen TDI owners/testers out there to see what the final results are.

However, in theory I would tend to think that if cooler air is provided to the intake manifold by the intercooler in cold weather conditions, this would presumably provide the added increment of power needed to compensate for the extra aerodynamic drag caused by denser air flowing around the vehicle.

I mean, dont't TDI engines operate in a perfect universe where no energy is gained and none is lost, whatever the change of conditions? ;-)

Steve

P.S.: How do you display a Graemlin?

Leave the intercooler alone.

If you mean not to tamper with the intercooler RAM air inlet in the bumper, I quite agree.

Today, I followed some of the advice suggested in previous posts and used foam insulation normally used on pipes to cover the centre grille on the front bumper but left the intercooler RAM air inlet uncovered.

Black insulation for the bottom portion and gray for the top portion to make it less conspicuous. Very easy to install indeed!! More so than my piece of carpet which heretofore I had to slide delicately through the plastic frame structure in the bumper before being able to lay it out flat up against the water rad.

I took the car out for a spin in -8 Celsius temp (I have an OAT gauge in my Jetta, a Radio Shack one that blends in very well with the OEM instruments) and every thing seemed normal. The engine reached operating temperature a little quicker than usual and then hummed along providing nippy accelerations on demand.

The real test will come when the OAT drops to -15 to -20C. I'll report back on the results if and then.

Steve

[ QUOTE ]
That is an interesting conclusion.... but since you covered BOTH the grille and the intercooler intake, it has little basis for fact. Perhaps if you UNCOVER the intercooler intake and see if the MPG drops again?

I wonder if anyone has taken any IAT (IntakeAirTemperture) readings before/after the intercooler in sub-zero farenheit weather?

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I've got IAT with and without covering...

IATs up to freezing with it covered are still cooler than summer IATs.

Mileage is benefited by having the IC covered.

BUT you need to watch the ambient temps. 35ºF is where I start thinking about taking it off (the intercooler cover).

You won't get better combustion with arctic air. You get lower combustion temps (below ideal) and you remove heat from the head (increasing viscosity of the oil) and you can increase wear if the head gets cool enough. how cool?

Well with out it covered my IAT was pretty much at ambient. -10ºC is not great for combustion efficiency.

BUT if you can't pay attention enough to monitor the outside air and combine it with your driving habits then don't do it.

I do it becuase I have a long sustained commute. Little call for an Intercooler, adn when I do use it, i generally have plenty of time for the heat to dissipate slowly... It still works to stabilize temp peaks, just takes a long time for the temp to drop.

I also monitor oil sump temps... and when I see them going over 200-210ºF I remove another peice of the covering on the radiator (think the movie Major League).

Summer sump temps are 190-210, unless i'm hammering at high speeds and then the temps'll go up...

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I've got IAT with and without covering...


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GeWilli, where exactly is the IAT sensor at?

Steve

(GeWilli) Thanks for sharing that info with us. Being of the technical sort of guy, I like to see measurements. (do you have color graphs with arrows and notes? /images/graemlins/grin.gif )


I am cutting some lengths of leftover pipe insulation tomarrow. These will be judicisly applied to the to IC inlet when the temps get below -5F this weekend.

I haven't looked at a TDI thermostat, but if it's like the G60/VR6 thermostats, the answer is simple:

VW had a problem of air blocking the cooling system when you tried to refill it. The 16V motors would get about half full then refuse to take any more coolant. When you cranked them up, they'd overhead because of the blocked air in the cooling jacket.

Then VW came up with a thermostat that cost 5 times as much because it had a tiny "check valve" on it. This supposedly let the air past (and it did just that). It also caused a slow "leak" which caused slow warmups even with the Corrados. With a TDI, even the tiniest of water past the thermostat would be enough to keep it from warming up.

I have an 82 Rabbit Diesel that absolutely warms up faster than any other car I've ever had. So much for the theory that all diesels have heaters that are slow---it CAN be done, and WAS, even in that primitive car.

Somebody should look at the TDI thermostat. I'll bet that if you replace it with a conventional one (which would fit right in), the warmup issue would drastically change.

Have you considered this? The Eberspächer heater. Here a few links one for the main website web page and the other for Canada web page Tim.