easy mods that I did recently on my Legacy 2017

- there are two coolant lines going into the throttle body making the throttle body sometimes 220F same as the engine which in my opinion is stupid if the goal for the engine is to breathe as colder air as possible. So what I did is I removed the both hoses and connected them with 3/8" od barb fitting from Home Depot. Subaru did good with plastic intake manifold which does not absorb a lot of heat from the engine so we do not need hot throttle body. The purpose of this is so in winter the plate does not freeze. I have read that some guys even in Canada with this mods do not have any issues in the winter.

The second mod is drilling 1/8" hole in the thermostat same location as the relief valve just opposite side. It will keep your engine at 196 F with AC on on 90 F day. In all other situations it will be much cooler than before but will never be under 196 F. It will help with eliminating air pockets during coolant changes and the temperature will have less hot cold spikes. There will be constant circulation of coolant with the 1/8" hole. Before the temperatures were going onto 217-220 range. If it is really hot outside and you do not have ac on it will behave like OEM setup, but once you turn ac on it will drop to 196F which is what you want. I do not like engines running over 200 F. With this mod no drops in MPG.

also do not forget temperatures at higher altitudes are on average 23F at 10000 ft, 5.5F at 15000 ft, -12F at 20000 ft, -30F at 25000 ft so there you go why you need TB to be heated.

Wait if you drill 1/8” hole on the thermostat housing wouldn’t coolant leak out?unless you meant the thermostat itself?

Good eye, you are absolutely correct. I expressed myself wrong. I will correct it.

I dunno…Subaru spent millions of dollars in testing and engineers put that particular t-stay in there to ensure that the engine operates at xxx degrees for a “reason”.

This is just my opinion, but I think the risk/reward factor here is non-existent.

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I dunno…Subaru spent millions of dollars in testing and engineers put that particular t-stay in there to ensure that the engine operates at xxx degrees for a “reason”.

 

This is just my opinion, but I think the risk/reward factor here is non-existent.

 

 

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I am sure that they have tested engines for a long time, and their main goal is to squeeze every drop of the fuel so they can put it on the paper and say "look how economical this car is." However, I do not think they think beyond 10 year of people owning their cars. Heat is the killer of automatic transmissions.

I will sacrifice one oz of fuel for the head gasket and transmission any time.

And most thermostats are fail safe, what about if thermostat fails to stay open when it fails? - you have the overheating engine and probably head gasket to pay for. In my case I will have at last some circulation and fans will kick on and keep cooling recirculating coolant. At the end of the day it is very cheap modification new thermostat is $15.

Are you sure that there is significant heat transfer from the throttle body to the air going through the intake? Living in Canada, I would probably leave this in place given the -20 to -30C temperatures that we regularly see. I would hope that there would be a control valve of some sort that is references to IAT so that this is not happening in the summer. Seems like it could be a real problem down south in very hot climates.

- there are two coolant lines going into the throttle body making the throttle body sometimes 220F same as the engine which in my opinion is stupid if the goal for the engine is to breathe as colder air as possible. So what I did is I removed the both hoses and connected them with 3/8" od barb fitting from Home Depot. Subaru did good with plastic intake manifold which does not absorb a lot of heat from the engine so we do not need hot throttle body. The purpose of this is so in winter the plate does not freeze. I have read that some guys even in Canada with this mods do not have any issues in the winter.

- there are two coolant lines going into the throttle body ... which in my opinion is stupid ... The purpose of this is so in winter the plate does not freeze.

Wrong. The purpose of throttle body heating is to prevent icing under conditions of moderate temperature (40-90 F) and high humidity, which can keep the throttle plate from closing completely. Heat transfer to the induction air is minimal.

FWIW, throttle body heating has been standard automotive practice for decades. My fuel-injected 1988 Pontiac Fiero V6 had it; my fuel-injected 1991 Buick Regal V6 had it. Every pilot is taught about the hazard of induction system icing, and how it can occur in both carbureted and fuel-injected aircraft engines.

The second mod is drilling 1/8" hole in the thermostat same location as the relief valve just opposite side. It will keep your engine at 196 F with AC on on 90 F day. In all other situations it will be much cooler than before but will never be under 196 F. It will help with eliminating air pockets during coolant changes and the temperature will have less hot cold spikes.

By the way, aren't you the same guy who, in another thread, was complaining about coolant temperatures in the 220s? My humble advice is to address the real problem, if there actually is one, before trying band-aid fixes ... and before recommending them to others.

Wrong. The purpose of throttle body heating is to prevent icing under conditions of moderate temperature (40-90 F) and high humidity, which can keep the throttle plate from closing completely. Heat transfer to the induction air is minimal.

 

FWIW, throttle body heating has been standard automotive practice for decades. My fuel-injected 1988 Pontiac Fiero V6 had it; my fuel-injected 1991 Buick Regal V6 had it. Every pilot is taught about the hazard of induction system icing, and how it can occur in both carbureted and fuel-injected aircraft engines.

 

Bad idea. This is an old-school solution for a problem that doesn't exist in our Subarus. Thermostat bypass is provided elsewhere in the cooling system design (e.g. the heater loop), and "air pockets" are nonexistent around the Subaru's low-mounted thermostat. Consider that thermostats with factory-provided bypass holes are readily available off-the-shelf, but Subaru elected not to use them.

 

By the way, aren't you the same guy who, in another thread, was complaining about coolant temperatures in the 220s? My humble advice is to address the real problem, if there actually is one, before trying band-aid fixes ... and before recommending them to others.

OK. you can think whatever you want Sir. but I have never heard of icing between 40F-90F especially under the hood where all the heat from inside the engine is moving up and heating under hood area. Intake air going through dry paper filter is going to eliminate most of the moisture and if there is any it will evaporate by the time it reaches intake.

Also connect the scan tool and drive in bigger city like Chicago with a lot of stop and go traffic in 90F with AC on. You will see the temperature going to 221F and the needle still shows normal. I am not saying that there is anything wrong, it is just too hot in my book for engine to take this high temperatures every day in during summer seasons. If you live in areas with low traffic you do not have anything to worry. But as I said connect the scan tool see the numbers for yourself then comment.

... I have never heard of icing between 40F-90F ...

Source - U.S. Federal Aviation Administration:

Yes Sir, but this does not apply for cars at sea level. Just like on the 10000 ft mountain you can boil eggs at 20F less than at sea level and pilot's blood can boil at certain altitudes due to the pressure differences this extremes we can not say apply to cars on the ground. Here is one simple question for you from a very simple man. Did you ever open your car's hood after driving for 1 h or more at 90F outside weather. Did you feel the heat that hits you in the face? There is no way I can expect to see icing on the throttle body or anywhere on the engine in that situation.

Thank you for the informative chart I will consider it if I ever learn to fly a plane. But chances are I am not that lucky.

Also do not forget that the temperatures at higher altitudes are on average 23F at 10000 ft, 5.5F at 15000 ft, -12F at 20000 ft, -30F at 25000 ft so there you go why you need TB to be heated on the planes. And that is why you see snow on the top of the mountains, and at sea level people are swimming in the ocean.

... this does not apply for cars at sea level.

Uh ... yes, it does. It's entirely a function of ambient temperature, humidity, and pressure drop across the throttle plate. Induction icing is more of a problem with carburetors, due to the fact that a carburetor's throttle plate is downstream of the fuel jets (which provide substantial evaporative cooling), but it is still a potential problem with fuel injection as well.

I can understand that for a carburetor with a throttle plate downstream of the fuel jet the heat of vaporization of the fuel can bring the temperature well below ambient, but for modern direct injection engines, or even port injection, the fuel is vaporized after the throttle body, correct? If so, with ambient temperature above freezing, what would cause the water vapour in the intake air to freeze?

Even at very high altitudes, the freezing point of water is essentially 0 C.

Uh ... yes, it does. It's entirely a function of ambient temperature, humidity, and pressure drop across the throttle plate. Induction icing is more of a problem with carburetors, due to the fact that a carburetor's throttle plate is downstream of the fuel jets (which provide substantial evaporative cooling), but it is still a potential problem with fuel injection as well.

... with ambient temperature above freezing, what would cause the water vapour in the intake air to freeze?

Good question. The abrupt pressure drop across the throttle plate, especially at idle and during closed-throttle deceleration, is also accompanied by a temperature drop.

Good question. The abrupt pressure drop across the throttle plate, especially at idle and during closed-throttle deceleration, is also accompanied by a temperature drop.

How can this happen if the intake air temperature at 90F ambient temperature is 145F according to scan tool? It is basically like trying to freeze something while heat gun is constantly blowing at it inside of the 220F room.

Just putting my 2 cents in..I have a 3.6r so might run a little different..I have a damd performance wheel and can see water n oil temp on my steering read out and just last week I was drivin in 90+ degree weather for 6hrs with A/C on and my water temp never climbed over 200 and oil temp was around 204.. There was a point climbing a grade and water didn't go over 218° and Oil Climbed to 220°...

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Just putting my 2 cents in..I have a 3.6r so might run a little different..I have a damd performance wheel and can see water n oil temp on my steering read out and just last week I was drivin in 90+ degree weather for 6hrs with A/C on and my water temp never climbed over 200 and oil temp was around 204.. There was a point climbing a grade and water didn't go over 218° and Oil Climbed to 220°...

 

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Sir, on H-6 fans run little different from H 4

your fans kick in certain percentage at certain temperature it is PWM controlled. Example: 30% speed at 185F 50% at 195F 70% at 210F - just an example

on h4 fans kick on at 215 at low speed and at 220 F at high speed (something like that, I am not 100% sure about the numbers but there are only two temperatures and two speeds High and Low. - which is shitty setup in my opinion. If you have a project car I suggest you look up coolguy.com and get PWM Fan controller from him.

thank you for your input. - Al

Quote:

Originally Posted by ammcinnis View Post

Good question. The abrupt pressure drop across the throttle plate, especially at idle and during closed-throttle deceleration, is also accompanied by a temperature drop.

How can this happen if the intake air temperature at 90F ambient temperature is 145F according to scan tool? It is basically like trying to freeze something while heat gun is constantly blowing at it inside of the 220F room.

ammcinnis, please Sir answer my above question.

How can this happen if the intake air temperature at 90F ambient temperature is 145F according to scan tool? It is basically like trying to freeze something while heat gun is constantly blowing at it inside of the 220F room.

Reply

How can this happen if the intake air temperature at 90F ambient temperature is 145F ...?

The temperature drop across the throttle plate is entirely dependent on the pressure drop; it does not vary with the intake temperature.

That said, while I'm not going to do the calculations, I agree that TB icing is probably extremely unlikely with an IAT of 145 degrees F. Even the FAA graph would agree.

Which brings up the question: How is it you're seeing an IAT 55 degrees F hotter than ambient? My IAT normally reads no more than 5 to 10 degrees above ambient. Are you by chance running an aftermarket "Cold Air Intake" or some other induction mod?

The temperature drop across the throttle plate is entirely dependent on the pressure drop; it does not vary with the intake temperature.

 

That said, while I'm not going to do the calculations, I agree that TB icing is probably extremely unlikely with an IAT of 145 degrees F. Even the FAA graph would agree.

 

Which brings up the question: How is it you're seeing an IAT 55 degrees F hotter than ambient? My IAT normally reads no more than 5 to 10 degrees above ambient. Are you by chance running an aftermarket "Cold Air Intake" or some other induction mod?

No I never play with cold air intake. IAT sensor is inside of MAF it is possible that it is somehow picking up hot underhold air. Or in stop and go traffic on a hot day when cooling fans turn on, the hot air is pushed under the car and it could be sucking the same air back in. I am not sure. Stop and go in big city traffic is horrible on cars. I am in Chicago and traffic sometimes can be like a parking lot.

I will try to wrap around the sensor just for testing purposes just to see if it changes. But now when I think about it even at highway speeds it will read 25-30F more than outside temperature. I have the ultragauge constantly connected to obd2 and constantly monitor live data. OTC Genisys professional scanner also sees the same temperature.

Eh this all sounds like a solution in search of a problem.

I agree it is not for you, most people that do mods. most likely know what they are doing have money to buy new part if they change their mind.

I like to experiment even if I know that there is danger of something going bad.

So you either have a heart to do it or don't. What I did is nothing too complicated. The worst thing you can do is spend money on buying new OEM Thermostat.

Sir, I respect your input. Maybe manicure pedicure or cooking is more up your ally Sir.

Sir, I respect your input. Maybe manicure pedicure or cooking is more up your ally Sir.

aki, Your posts are interesting .... but with great respect, I'm not sure that the above particular comment is deserved.

P.S. just to show that we are not all perfect ... I think you meant "alley"

Maybe ....

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