Just got an ultragauge and noticed that my coolant temp never really gets above 180F. I've never owned a car that operates that low. Even my boat barely operates that low and it's an unpressurized open loop cooling system.

I drive 90% highway everyday and I'm kind of wondering if installing a warmer thermostat would increase fuel efficiency. I can't really see this car overheating the way I drive. Most of my other cars have had around 195 thermostats and people have always asked about putting cooler ones in and everyone posts about how it kills fuels economy to do that even when programmed properly.

 

I do not know what thermostat comes stock in a FIT. My Colorado came standard with a 180. I have never seen over 185 in the summer and 174 in the winter. You are already running very thin oil. No reason to heat it and the trans fluid up any more than necessary.

I'll have to install my Scan Gauge in the Fit and see what it reads. I would be delighted to see it at 180.

 

The t-stat in my CR-V opens at around 180 - 185F

Cooling fans engage at ~195 - 200F




Rather than trying to modify the Fit, why not just replace the thermostat to verify proper operation?

In my experience, you are best off to buy OEM with Honda thermostats, BTW. They come with a new sealing O-ring (most aftermarket 'stats do not).

 

My understanding is the stock t-stat is a 170 or 172 so if it's reading between 170 and 180 most of the time, I'd say it's working properly. I was just thinking a 180-185 like your CRV would be beneficial for economy.

If the engine ran at around 190-195, I'm sure that would help but if the cooling fan kicks on at 190 and/or the ECU retards timing to help cool the engine, then the fan would probably run all of the time and the timing retard would counter any potential gains of a warmer engine and potentially lower economy.

Even at 190-200F, there is still a pretty good safety buffer for the oil and coolant. If you're getting significantly above that during normal driving, there is something wrong and it didn't sneak up overnight.

 

If changing to a warmer thermostat would give better milage without any significant drawbacks, don't you think Honda would have already made that change? I mean, it's not like people purchasing economy cars are interested in economy or anything like that...

I think I'd trust their initial design rather than attempting to tweak it further. If you do suspect the thermostat is malfunctioning, by all means check and replace it if it's broken; but why take even the minimal risk of using a different temperature rating when there's no real hope of success?

 

Everyone says that about every car ever made and yet the simplest of people always figure out a way to use simple bolt on mods to increase power and/or economy. The OEM has to make compromises on everything. Weight, power, reliability, cost, etc. Sometimes, in order to keep the average person who doesn't pay any attention to their car from destroying it, you have to make compromises in both power and efficiency. So to say that the OEM made the car to the pinnacle of everything you want is making a very bold statement.

 

Hey there, I've been wondering the exact same thing. When I hooked my maxitrip (Princess Auto scangauge) a year ago when I bought this 2007 I was dismayed to see temps of 77C or 170F. Thought tstat was toast. Looked online and Rockauto says this is the stock temp. Weird as most modern engines have gone to 195 for higher efficiency.
I've had a long association with Honda including a few years as a parts and service guy so second guessing them and popping in a 195 is not gonna happen without understanding why they designed it this way.
I thought a little googling would tell me why but I've been stymied. This isn't a full time obsession by any means but I've looked a fair bit. I get some work done by the head mechanic at a nearby dealership. He is a car guy from way back, GM originally, but Hondas for about 25 years. He has no idea. With the Jazz and City being out for more than ten years I figured someone would be talking somewhere in the world - nada.

My own lame-assed theories are 1) That this design runs MUCH cooler in its boat incarnation (with different temp thermostats for head and block) and bad things might happen with clearances if run much hotter. 2) The position of the thermostat seems a little lower than traditionally, maybe they've found that 170 there equals the same overall temp as 180 or 195 at a higher point on the engine.

The quest has become more urgent now because I notice that the temp is wavering 10 or 20 deg below 170 now. Winter is coming on but it's not really that cold yet and it had no trouble getting to 170 last winter. Honda's parts list only shows the stock temp but I may try a 180 Stant 45878. A little hotter rather than the big leap to 195. I'd prefer the OEM and may try to extrapolate the Honda part # using stants list of what fits what (looks like this thermostat fits a BUNCH of other Hondas.
I'm not concerned about making the fan cycle because the switch for it is usually at the BOTTOM of the rad which is gonna see even less hot water with a hotter stat. (will confirm of course).

So, looong story short (sorry), any gurus lurking out there with the inside scoop on the reasoning behind this design? Anyone tried this and willing to share results?
Northern states and Canada probably most likely?

 

Here is something I found on the fit. Honda Fit: New Coolant Passage Runs From Block to Head -- Tech-On!

Water enters the block first and then the head. This would certainly make the head warmer but it also makes me think that the danger of overheating the critical parts in the engine is even lower. Even with warmer coolant hitting the hot head last, I still don't see the coolant heating up to such dangerous temperatures that you would start to boil over the coolant...or even get a knock.

When I owned a Jeep Cherokee, it used a 195° t-stat and generally ran around 210 during the summer. The Jeep's 4.0L engine also pumps coolant into the block first. Jeeps were (maybe still are) notoriously unreliable and had piss poor cooling systems but the engines were bulletproof. There were many times when my jeeps engine hit 235° or more after I installed a crappy electric fan that didn't work right. I could smell it, it was so hot and it worried me but it ran like a champ for many more years before I sold it.

On a side note, I know boats run lower temperatures because most have open loop cooling running maybe 2-3psi with regular water. This low pressure allows some small air pockets to form around the engine causing hot spots and areas where the raw water can boil if it gets too hot. Most cars run closed loop at around 15psi and use coolant which boils at a much higher temperature so much much lower risk.

I plan to slap a 180F t-stat in my fit sometime soon but with it being holidays and lots of stuff going on, it may be a few weeks before I can get to it.

 

Good find. Interesting, especially the aluminum (eek) exhaust manifold with coolant circulating through close coupled to the hot convertor. I wondered why the inlet and outlet were so close together, the circuitous route explains it.
Scroll down in this to the cooling system link and watch video about the cooling theory in the outboard :
Honda BF90 Outboard Engine - 90 hp boat motor specs and features

 

Apparently this thread got called out on hondafitforums "More incorrect advice" thread. http://www.hondafitforums.com/showth...?t=1235&page=4

If you aren't familiar with it, it's basically a guy named Claymore who trashes other people for posting information that is incorrect or at least that he doesn't agree with.

@Claymore, if you're reading this, would you care to explain? Even in your thread, you talk about how no one understands the stock operating conditions but you neglected to state how we are incorrect. I came on here for help and to better understand. You say DrewE on here has the correct answer by saying that the OEM knows best and you should trust them instead of tweaking something. That's very interesting considering you have a big thread on how you didn't like what the OEM did and decided to change to a lower temp thermostat and fan switch... DIY low temp thermostat and fan switch - Honda Fit Forums

Not trying to really call anyone out here but if you know the right answer to a question but would rather make fun of the question rather than provide the correct answer, that's pretty cowardly....

 

LOL Claymore THANK YOU from the bottom of my heart for your tremendous contribution from afar to the discussion. Lots of specifics there! Why do you have a forum - no discussion required other than "that's the way it is leave it alone"?
Drew I'm sorry if I offended you by asking questions although it's entirely possible I haven't. You gave good advice, advice I've repeated MANY times myself personally and professionally.
If Clay had read my post he would have seen I am very leery of second guessing Honda engineers and so want to understand the system well before I jump in. I understand cooling systems VERY well, particularly Honda, but this one is very different.
I, and I think the OP are trying to understand the thinking that went into using a thermostat 10 degrees cooler than the worldwide, longtime, industry norms of 180 or 195.
If clay's short baseless rant has enticed anyone over here that has REAL INFO to offer PLEASE join in!

I'm not much of a joiner anymore - a bazillion user names and passwords to keep track of, screwy rules, and the inevitable nasty confrontation which in this case has only taken ONE DAY.

Like I said, I've googled a lot and saw nothing on any forum that helped. When I saw the OP asking the same questions as I had I decide to join in.
Sorry for offending the sensibilities ONE MEMBER of another forum?

 

@hank — Absolutely no offense taken. Asking questions is A-OK with me. Disagreeing is even A-OK with me, as there are times when I unintentionally offer less than perfect (maybe even wrong) advice. If Claymore wants to feel offended on my behalf, that's his (or her) problem, I guess.

I don't claim to have any particularly deep understanding of the Fit's cooling system. I do understand that fuel milage is a pretty important selling point for economy cars; and I'm pretty sure that Honda's engineers, while not infallible, are pretty smart. Based on these, I can only conclude that if something as simple and basic and cost-effective as using a warmer thermostat would yield any increase in fuel milage without compromising something else important (like engine life or emissions compliance), they would have long ago made that change.

Nevertheless, I certainly won't stop anyone from fiddling with their own cars if they wish, and would still be interested in hearing how things turn out. I'll be keeping my own car stock in this case, though.

 

 

That is very clear now. He still refuses to come on here and speak but apparently loves to read posts here anyway. I thought I'd check back on his forum to see what he cowardly says to his own clique in the event there was some knowledge to be had. Some of his information shows reason but not all of it which leads me to believe that most of that knowledge comes from forum reading and blind part changing vs actual engine building, tuning, or even the laws of physics for that matter.

Once I get some time, I'll try the warmer thermostat and let people know how it goes.

For the record, I've never been to any forum except that one where an administrator blatantly calls out people for fun and to massage their own ego. Most administrators won't even put up with that crap much less do it themselves. Glad I found this forum first.

 

Thermostats are specified by the temperature the thermostat valve BEGINS to ope so its not usual for engines running at conditions that need more heat transfer would operate at a temperature greater than temperature the valve begins to open.
The problem engine designers have is being sure there is enough colant flow when the vave is wide open to flow enough coolant to prevent the engine from overheating. Coolant from radiators to water pump generally cool the head first because thats where the greatest heat load is and naturally you want the temperature difference at maximum to carry away the most heat and passages such that the heat transfer is evened between cylinders (which generaklly means greater transfer from the middle cylinders.
as faras scangages are concerned the temperature that matters most are the head temps which generaklly not where the sensors are.
In short just because your engine designer speced a 180F thermostant doesn't mean that the temperature where it matters most, just incative of it.
There's nothing wrong with trying a higher temp thermostat as long as you put sensors on various parts of the cylinder head, block, overfloews with various engine loads - usually established on dynomometers - to monitor tthe engine performance. We always used color-coded smears as well as thermocouples and exhaust analyzers - on each cylinder - to find out whats going on, just a Honda engineers.
Its OK to experiment but not at the risk of a burnt valve. Unless its your job and to have a budget to cover.
cheers.

 

So I wanted to give my experience with installing a warmer thermostat. I changed a properly functioning stock thermostat (170-172) with an aftermarket 180 thermostat. First off, it's not a hard job but it's a bit annoying because it's way harder than it should be IMO. My original engine temps typically fluctuated between about 176 and 178 and would occasionally hit 180. With the new thermostat, my engine temp typically fluctuates between 184-188 and occasionally hits 194. IMO that's still well within a safe limit. I think Honda feels the same because if I sit in the garage and let it idle, the ECU will not turn the fans on until the engine temp is past 220 but I've been assured that's normal even with a stock thermostat.

I have every fill up documented since I bought the car. At this time, I'm using the last 8 fill ups and approximately 2000 miles before and after the thermostat change. Average mpg with the stock thermostat was 31.2mpg and average with the 180 thermostat is 33.3mpg. All of this data is based on actual mileage compared to the amount of fuel put in the tank. I do my best to ensure the tank is always topped off completely and don't stop when it cuts off the first time. All of my fill ups are typically mid late afternoon because that's when it's convenient.

Now for some numbers and sanity check. The current mpg increase yields 6.77% but the gains fluctuate between about 5% and 7% depending on how many tanks I use for my comparison. I'm a very warm natured person so I almost never run the AC unless it's over 90 degrees or I need it for the defroster. That said, if I've used the AC in any of the tanks currently being used for comparison, it would've been extremely minimal. However, with the change happening in December, the numbers used after the change were taken in consistently colder temperatures which means the engine is running longer in the wasteful open loop configuration. I always get the best fuel economy in the spring and fall and feel like the numbers could go up some more when spring hits and I'm getting better gas mileage again.

Obviously, even a 7% change isn't going to make you rich. Using my average 22k miles a year and $3.30 a gallon, I'm only saving about $150 a year. However, it is an easy mod that I see no drawbacks to. I get better fuel economy, the heater works better in the winter so I'm warmer, and I'm seeing no adverse engine problems. I have about 4k miles on the oil and no oil has been burned and it still appears to have a nice amber color to it.

 

In summary you are saying that a 6 degree rise in engine temperature gave you almost a 7% increase in mileage.

Interesting. Please keep us advised on how it goes in the future.

 

More like a 10 degree rise in temp on average but yes that's what I'm saying. I agree it sounds too good to be true but I haven't really changed my driving style. With the current numbers being used, I haven't even changed the oil either. I've got 5100 miles of data on the old thermostat so I'll continue to track the differences and if things change, I'll be sure to keep everyone posted.

 

Quick update... I've had 5100 miles on the OEM thermostat and 5400 miles on the new warmer thermostat which comes out to 20 fill ups on each. As of now, the increased fuel economy is 5.2% with an average of 31.4mpg on the OEM and 33.1mpg with the new thermostat. Winter will not go away so I'm still getting worse fuel economy because of that and the OEM thermostat has more tanks of warmer temperatures without A/C than the new one but this is the break even point for mileage/tanks.

Like I said before, this change won't make you rich but it is an improvement with evidence to back it up. I'd certainly do this thermostat swap again but because the thermostat is in such a ridiculous location on these cars, I can't say I'd do it without having to do something else in the area.

 

Nice follow-up, THANKS


Give us another update after 3 more months of driving!