I wrote this up on another forum and thought I would share it here as well. A lot of people will just slap on parts with no thought to what they are doing. When it comes to cooling, most people just think the cooler the better right??? Let me just throw on a mega oil cooler, a huge radiator, a lower thermostat, etc. Keeping the engine fluids too low can cause unforeseen problems. For those with Subarus or coolant based oil coolers like the Subaru models, if you run the coolant TOO cold you may not be removing impurities from the oils. Why would I have impurities in the oil you might ask? There are many factors that can lead to contaminants in oil. Water vapor from condensation is one of them. As the engine cools, so to does the air in the crank case and oil passages. Water has a boiling point of 100* C or around 212* F. If your oil NEVER reaches that point and you have a closed crank case system, it will be very slow to leave the engine oil. Another thing to consider is the gasoline that comes into your oil supply. This will happen on just about any motor through minor amounts of gasoline coming into the engine oil by way of blowby. The more you push your motor (especially turbo motors) the more blowby you will have. Peterson Fluid systems has estimated that the average motor will have about 2% of the air moved through the motor escape past the rings in the form of blowby. 2% may not seem like a lot, but if you take a motor with a Garrett GT35R turbo or Borg Warner S300SX you are talking about around 1000 CFM of air movement. 2% of that would be 20 CFM!! This will carry the byproducts of combustion with it, including gasoline, water vapor, etc. Below is a manufacture's report on their gasoline. As you can see, at 50*-70*C or 122*F-158*F only 10% is evaporated. Bring that temperature up to 100-121C or 230-250*F and the amount increases dramatically to 50%. Now I am not advocating running the engine oil at 230* F, just illustrating the point that the lower the engine oil temperature, the less gasoline is being removed. Specifications define the temperatures at which various percentages of the fuel are evaporated. Distillation limits include maximum temperatures that 10% is evaporated (50-70C), 50% is evaporated (110-121C), 90% is evaporated (185-190C), and the final boiling point (225C). A minimum temperature for 50% evaporated (77C), and a maximum amount of Residue (2%) after distillation. Vapour pressure limits for each class ( 54, 62, 69, 79, 93, 103 kPa ) are also specified. Note that the EPA has issued a waiver that does not require gasoline with 9-10% ethanol to meet the required specifications between 1st May - 15 September. Another thing to consider is the use of meth injection. As we all know this meth injection can have unburnt methanol make it into the oil. Meth has a boiling point of 148*F to 160*F depending on who you ask and the purity of the methanol. This should burn off pretty easily no matter your thermostat. But what about ethanol? Ethanol has a boiling point of around 79*C or 174*F. And ethanol is in just about every major manufacturer of gasoline in some amount, usually around 10%. The OEM Subaru STI thermostat specs: As you can see it begins to open at an average temperature of 172.5*F and becomes fully open at 196*F. I commonly see temps of 212*F on Subaru motors. On a hot day while sitting they can reach 215*F-220*F pretty easy if you really push them. This will definitely take care of the water in the system! It will dramatically raise the amount of gasoline evaporated. And methanol and ethanol won't even stand a chance. No drop in a thermostat that is fully open at 160* F and it may never reach the temperatures necessary to boil off the water vapor, gasoline and other contaminants as the temperatures may never make it over 200*F. The same would go for an oil cooler that is not thermostatically regulated. As contaminants build up, oil is diluted and now start the problems with turbo bearings, main bearings etc. On a stock car with stock clearances, this may be a much slower progress, but on a built motor, upgraded turbo, spraying meth or using E85, this could happen much quicker! All just something to think about and be more informed about before throwing a thermostat in the car. If you do, monitor your oil temps! Make sure they are making it to the points that they need to.
The AOS is going to have absolutely nothing to do with blowby mixing with the oil. All the AOS does is keep it out of the intake tract. The blowby will still mix with the oil in the crank case. The main thing is checking your oil temps to make sure they are reaching a decent temperature.
Here is another good article: http://www.carnut.com/ramblin/_cool3.html by Steve Jack HOTRODSRJ@AOL.COM Concept One Pulleys Jackstands at Old Cars Only A few of you good folks must have spotted other articles that I have done either in print or online about this subject. At the request of a few folks here I am putting this up for what it's worth and expanding some information about this as well. The argument is about running 160 degree thermostats and the good and/or bad results. Now keep in mind that thermostats have absolutely NO effect on your systems ability to cool, simply a regulator of the range it operates in. So, if you think a 160 will cure an engine running at 220 with a 180 thermostat...forgetaboutit! This is not about cooling capacity at all. The graph to follow illustrates the importance of how critical optimum coolant temperature is to the longevity and performance your engine. Cooler water makes horsepower and warmer water minimizes engine cylinder and bearing wear...or so it's thought, but only to their own limits and ranges. There is a range where both optimum performance as well as minimal wear share similar characteristics. That number lies in the 175-180 degree range as shown by the overlap in the chart which correspondingly requires a 180 degree thermostat. FWIW, higher operating temperatures of today's engines are to fight combustion by-products and pollution. Also, engine oils are designed to work over a specific temperature range with optimum performance starting at temperatures that require the coolant to be the very same 175ish range. And don't forget the moisture issue. Have you ever seen water vapor coming from your tailpipes? Sure..and the very same thing happens INSIDE your engine. YOur engine forms moisture inside when it cools and condensates on the walls of the inside. This moisture the is washed down into the oil when started and then awaits vaporization by internal temperatures rising enough to bring the moisture to the appropriate corrected vapor point (boiling). If enough moisture is left behind it combines with combustion byproducts to form acids that become dissolved in the oil itself. The oil becomes more acidic as the age of the oil progresses and picks on certain parts eventually. Also moisture will corrode other surfaces. So, it's important to get these engines to a satisfying operating temperature as soon as possible. Usually oil pooling temps are about 30 to 40 degrees higher than the coolant temps. This is a generalised statement and can vary with load and engine design but you can see why you want your oil over 212 degrees to boil out the moiture immediately! A 160 thermostat usually does NOT accomplish this temperature. Years of research show use of 160 degree thermostats is way too low to be considered for performance or engine longevity. As the chart above illustrates, engine wear increased by DOUBLE at 160, than at 185 degrees. The 160's were invented for and commonly used in older, open loop cooling systems where only 6 pound radiator caps were used, and low 212 degree boiling points were the limit. We know better now. Many early hot rodders found the 160's to be a smiggin better performing than the 190's, however the in between 180 appears to satisfy both ends of the spectrum. The correct water temperature and thus resulting metal operating temperatures required for the cylinders to achieve a minimum specific temperature in order to allow a fully mixed Air/Fuel charge to combust efficiently is a minimum of 180 degrees coincidentally. If you use 160s be aware that this can have a degrading effect over a time on your engine. I know alot of rodders still using them however to whatever ends they want...and that's okay. Heck, I know guys that run NO thermostat and most of you know that's another book to be covered. I just report what I learn...and you decide what's best for you. I hope this satisfies you information junkies out there. Steve Jack HOTRODSRJ@AOL.COM Concept One Pulleys Jackstands at Old Cars Only
Unless you are tracking the car regularly and running into overheating issues, I see no point in putting a lower temp thermostat in a car.
I tend to agree. Unless it is needed, best to keep stock heat range and put in a cooler that fails open. I am told there is one at Autozone now that has an open failsafe that is stock heat range...starts to open at 172* and is fully open by 196*f.
Heres a few things to think about. While oil and coolant temps are linked you can not address them like they are directly linked. Just because you install a 160 degree thermostat doesn't mean your oil isn't going to get to operating temp. The factory subaru oil cooler does a lousy job of cooling oil, there isn't enough surface area and its mounted right by the headers. If you are running into overheating issues on track then you have bigger problems than a thermostat. When the systems in these cars are bled correctly even with all stock parts (sti) they do not have cooling problems. More later
And I agree with those statements. Another reason why I could not answer the above question. If the oil is getting to temp, then it is fine But the other side is if the oil gets to temp in the winter months as well. If you extract too much heat out of the engine, it can be as bad as not extracting enough.
Yeah... this would all probably matter if you were one of those people looking to eek out that extra 1k miles per oil change. However like most enthusiasts we all change our oil way ahead of schedule.
No water doesn't change its boiling temps in a subaru... but if your changing you oil at regular intervals the oil contamination will be minimal. What I was saying is trying to compare and old school motor that runs much larger piston to wall clearances, ring gaps, and burn less efficiently to a newer subaru motor is silly. I can see the logic behind it in an old school cast iron block... but in the newer all aluminum blocks I can't.
Condensation still forms in modern motors just as it does in V8 right? Water still turns to vapor at the same temperature right? The below portion that I have cut out of the article still applies. Unless you think that gasoline, water, ethanol, all change their boiling points just because they are in a new motor... And don't forget the moisture issue. Have you ever seen water vapor coming from your tailpipes? Sure..and the very same thing happens INSIDE your engine. YOur engine forms moisture inside when it cools and condensates on the walls of the inside. This moisture the is washed down into the oil when started and then awaits vaporization by internal temperatures rising enough to bring the moisture to the appropriate corrected vapor point (boiling). If enough moisture is left behind it combines with combustion byproducts to form acids that become dissolved in the oil itself. The oil becomes more acidic as the age of the oil progresses and picks on certain parts eventually. Also moisture will corrode other surfaces. So, it's important to get these engines to a satisfying operating temperature as soon as possible. Usually oil pooling temps are about 30 to 40 degrees higher than the coolant temps. This is a generalised statement and can vary with load and engine design but you can see why you want your oil over 212 degrees to boil out the moiture immediately! motors correct?
I will try to explain it this way... SUBARU's run much tighter bearing clearances... much tighter bearing clearances mean higher oil temps at the bearings. Its not uncommon to see oil temps flash up 20-50F (almost to the shear point) between the bearings HIGHER then what you see elsewhere in the motor as indicated oil temp. Oil temps do not remain constant through out the block, which is why we try and run as much oil as possible in our race cars to even out the high temps seen between moving parts. In any event this rise in temp will be more then enough to burn off any "condensation". Now if you take an older engine that runs looser clearances you will not see drastic oil temp increases at the bearings. Hell 90% of the boats that run around on the lake never see coolant temps over 160f because they are pulling in cool lake water constantly... guess all those guys are screwed too, or maybe lake water boils at a different temp
Actually my boat ran at 205*F and had a thermostat in it It did not flow open water through the engine constantly. Of course it was an old outdated 350 motor, so I guess it has different laws that apply to it anyways. I will take Coolrex's car as an example. He constantly had a mixture of oil and water in his catch can. Where did that come from?!? The crank case. Condensation still happens regardless of the motor. I would hazzard to guess that 99% of all the driving done by 99% of the users and readers on this forum is done on the street and not on the race track. The above informational post was done to help explain to these people a little more about engine operating temperatures and how it might effect their car and the longevity of their car. This is not about race cars which will get their oil changed after every track day.
I understand what your saying... and I am not trying to discredit anything. But Crankcase vents are there just for this reason. Typically the vapors, moisture and all gets sucked back into the combustion process and not trapped inside the motor. Its one of the reasons why we don't see sealed blocks with no crank case venting.
Actually you are wrong, subaru is not by far the only manufacturer that utilizes tight tolerances. .0009-.002 oil clearances were being used on early to mid 90's ford modular engines. As far as the above the earths' atmospheres oil pressures go, running looser clearances solves these above stated issues. 90% of the boats on the water operate at between 185 and 210.
LOL... this link used from the OP as evidence of this theory http://www.carnut.com/ramblin/_cool3.html was based off old muscle cars, which are no way like the cars built now a days. You are correct that ford and other manufactures have been building cars to tighter standards.. but thats not what the link was about. So thank you come again... Also my brand new 2010 boat that has a small block chevy runs flat out on the lake with coolant temps in the high 150's to low 160's... so does my buddies Supra (boat) that also has an indmar (chevy) small block so did my 2007 Monterey.. oh wait and also a 2003 Baja speed boat.
Actually the link was not used for the OP. It was just an additional article I found interesting. I try to focus on building cars and maintaining them for longevity as well as performance. Not just all out performance. If I love 2 hp by sticking with a heat range for our engines but allows them to not corrode or have other oil based issues caused by contaminants, I am ok with that. As Matt said above, most of the cars out there are fine with the factory heating system...which was the original point of the whole OP.
Here I come again, I was commenting about your typical reference " Subarus are different from other makes" I was not commenting on the link, however the info. applies to old and new. My Donzai runs @ 200 Flat out and 190 cruising, you show me a boat that runs 160 I'll show you a boat that runs 200. Regardless, this is not a thread about fucking boats! Mike is correct there are many reasons other than the ones stated above for not operating engines @ low temps.