The time is coming for a new water pump and thermostat on the Boxster. The internet is full of people saying to get the lower temp option (71C) instead of the factory 84C. Reasons include: less wear, better fuel economy, etc.
Im skeptical. The only reason I'm even considering it is on warmer days the coolant temp will move up if I'm not moving. I think it's in the normal range still but it's hard to tell.
What's the deal? Is this worth it for a street car?
Won't that make for worse emissions? I remember lower-temp thermostats being the thing back in the 90s but I thought that was outdated wisdom now.
As far as I've read, the lower temp fools the computer into running a bit rich, to give "mo powr"
Sounds like a good way to get worse MPG to me, but I've never tried it.
In reply to brandonsmash :
Ya beat me to it! But I was skeptical then, as well!
But I didn't work on "tuning" FI till a few years ago
I'm an old school carb., or diesel guy, primarily.
Finally starting to catch up with the times!
I think the logic is that OEMs run the engines hot to meet emissions at the expense of engine life, etc. I'm not buying it but I'm asking here hoping some of the professionals pipe in with information.
Since "newer" engines run hotter, to get better emissions, and also they get better MPG, and last much longer than the engines I grew up on, I'm not following their reasoning, on that one.
Big nope on that one, lowering the thermostat temperature should be a last resort to mitigate serious overheating problems and is an especially questionable idea on less-antique engines. 84C is totally normal for an engine from that era and 71C is super low.
Unless you also bring down the fan trigger temperatures, I'm pretty sure it just delays the onset of high temperatures rather than actually preventing them, considering I'm pretty sure the engine is operating at more than 185F most of the time. That's a change from basically 185F to 160F which is a *big* difference. If it was like 5-10F I'd think there might not be much harm in trying it. FWIW from what I remember the coolant gauge does actually move around a bit on those cars in normal operation. New water pump and fresh coolant will probably improve things too. If anything what I'd do is figure out how to wire in a fan override switch, iirc the low speed fans don't come on until like 210F or something slightly ridiculous seeming. (It's been like eight years, don't quote me on that but it was higher than I expected)
You want higher temps for better economy. The hotter the engine, the less combustion heat is lost to the cooling system.
In the 80s, some manufacturers, I know Ford for sure, were working on engines that could run without cooling systems. If 30% of fuel energy is wasted through the cooling system, eliminating the cooling system represents a large increase in efficiency! We obviously don't have that but we do have engines now with thermostat opening temps in the 230F+ range.
USUALLY, generally speaking, etc, hotter engines also wear less. They also CAN make more power, too, depending on a lot of other factors.
I can't think of any automotive engine that I would want an 160°F thermostat in. (Eagle units for those, such as myself, who aren't able to convert to Celsius easily in their heads) I even ran 190° (88°C) in my old carbed big block MoPar drag engines, and considered anything lower to be a crutch for other issues that needed to be remedied.
spandak said:The time is coming for a new water pump and thermostat on the Boxster. The internet is full of people saying to get the lower temp option (71C) instead of the factory 84C. Reasons include: less wear, better fuel economy, etc.
Im skeptical. The only reason I'm even considering it is on warmer days the coolant temp will move up if I'm not moving. I think it's in the normal range still but it's hard to tell.
What's the deal? Is this worth it for a street car?
As others have said, reality is the opposite of what "they" claim.
And the t-stat does little to the temp when the car isn't moving. On normal tests, we would expect to see temps up to 215 or so.
Lower temp will usually burn more fuel, not less. And unless the cooling system is big enough and the fan set points can be adjusted, it makes for bigger temp swings in various conditions.
Personally, I'm a big fan of not running engines any colder than necessary. Ideally, you want to keep the intake temps down, but coolant temps high unless you desperately need a little extra knock margin.
That factory 84* C thermostat is only 183* F. That's relatively cold already for a modern car. Heck, the M62TU in my BMW runs normal coolant temps in the 215 - 230* range (and a 28 psi pressure cap) to squeeze out a little extra efficiency. The only downside of it is somewhat shorter lifespan of plastic parts in the cooling system.
The small block Mopar in my Jeep runs a 195* thermostat factory, so normal coolant temp range is 195 - 210* or so. Part of the reason I started doing my own tuning on that thing is that all of the mail order "tuners" out there didn't really want to touch it unless I put in a 180* thermostat (which it doesn't need and I didn't want to do). All of the performance guys claim you have to run it colder once you start modding to get the intake temps down and avoid pinging and that running warmer will cost a ton of power and is just for "emissions crap". Yet somehow, despite iron heads and a small bump in compression over stock, I still have plenty of knock margin at the higher temps and it performs just fine.
Even on the boat I tend towards warmer thermostats. People got so used to boats with open cooling systems running super cold by necessity, so that became the norm even with closed loop systems that can safely run warmer. Swapping the factory 143* thermosats in the 454s for 160* made them run significantly better at idle and under light loads. Going up to the 170* thermostats they have now was even a small further improvement and also reduced the temp swing between light load and heavy load (they got up into the 170 - 185* range under heavy load regardless due to how the cooling systems are sized).
The context matters here, in that the car in question is a Boxster. I also have a Boxster, and I did put the lower temp thermostat in it, so I can comment on it before and after in all weather conditions. First, the Boxster has a huge and convoluted cooling system, that has some vulnerabilities. It takes a long time to warm up, and has issues with airflow through the radiators and cracking plastic bits. Having a bit more headroom can be a good idea on these.
The thermostat I used was in an aftermarket box, but is an OEM part, with the Porsche part number stamped in it even. From what I understand these are fitted by Porsche in other countries.
With the original thermostat the temperature when running steady was about 190 ish, the needle was on the far side of the 8 on the gauge at 180, and the gauge is a real gauge and matches my scan tool. After the change the needle is on the colder side of that same 8, and the car runs right about 180 on the scan tool at steady highway. There has been no change in fuel economy. The car gets onto the normal operating temperature running tables in the ECU. There is no negative impact. When in traffic, the temp will climb up to the same set cooling fan set temp, but it has Moore headroom before it gets there, on this fragile engine, and I'll take that bit of extra room on this car with no negative impact.
Bigger temperature swings between sitting in traffic and cruising are a bad thing in my opinion. Fan set points shouldn't have a lot of headroom. If it heats up 25* sitting in traffic before the fans kick on, then cools back down when you're moving again, unless you have a very high rated pressure cap that doesn't vent off any pressure when it heats up in traffic, you end up with lower cooling system pressure when cruising after it has gone through a heat cycle in traffic and come back down. Lower pressure is bad, as it means more chance of very slight boiling in the hottest part of the heads, etc. And that leads to both worse cooling system performance and also those hot spots getting hotter, increasing the chance of spark knock (or performance reducing knock retard on an engine with knock sensors).
Ideally, the cooling system should keep temps as stable as possible with the combo of radiator sizing, fan trigger points, thermostat temp, system design, etc.
I always figure the manufacturer's engineers went to a lot of trouble to determine the optimum thermostat setting, all factors considered. To think that I could outsmart them and "improve" my car by installing a cooler thermostat is highly unlikely.
Sonic said:When in traffic, the temp will climb up to the same set cooling fan set temp
So you're saying it won't do anything to improve the one actual complaint OP has, about temps rising while sitting still.
The "right" solution is to make the fans come on earlier, or give yourself the ability to override it. On mine, the A/C didn't work but did still kick the fans on, so that was convenient.
spandak said:The only reason I'm even considering it is on warmer days the coolant temp will move up if I'm not moving. I think it's in the normal range still but it's hard to tell.
As others have said, this is not a problem that needs fixing. This is just standard physics - without moving air over the radiator, the only cooling is through natural convection (hot air rises) which is woefully inadequate for a vehicle. If you aren't tripping the fans, temps are cool. It might burn your hand, but the engine is happy. "Cool" is obviously relative. Even you open the thermostat but blow no air over the radiator by moving the car or turning on a fan, temps will rise.
Now, if temps continue to rise like nothing happened after fans turn on, you have a problem somewhere that needs to be addressed, but that a different issue.
I've never over heated but the temp rise does make me nervous if I'm honest. Replacing the engine is not an option and it's my daily so keeping it happy it's important to me.
Most of my driving is at speed, my commute is 30 minutes of 90% freeway. In those conditions the temp sits in the middle of the 8 on the dash. Probably 185ish. I've seen it climb all the way to the next tick mark before. Once it's into the 0 I turn on the AC to get the fans going. After that it goes right back down.
Does anyone know what temperature the upper tick is on the gauge? Napkin math interpolation says maybe 215 but that's seems high for an aluminum head/block mid engine German car that's 25 years old.
This is why cars don't have temperature gauges anymore.
If it isn't in the red, it isn't bad. It sounds like the system is operating as designed, so I'd trust it and put my worry elsewhere.
For what it's worth, the fans don't even kick on for my 20yo Toyota until 208F.
It's been a while but iirc the low fan trigger is around 210.
Remember that your new water pump and coolant will only help things. My only real desire to bring temps down on mine was during rallycross when it basically lived at 210+, because hard use, high engine speeds, low vehicle speed, and then park it for a couple of minutes and repeat - pretty far outside of intended operating conditions. I couldn't help but notice the gauge moving around in normal driving but was never particularly worried about it. Honestly if you have that level of concern......I'm not saying it's unreasonable, but an m96 engine in a daily driver is probably not the right choice for you in that case.
LS swap it
(sorry, figured the thread needed this sort of levity)
Keep in mind that thermostats don't just snap open. It's usually fully open 15 - 20 degrees (F) above the rated temp, so any temperature between thermostat opening temp and about 20* above it is normal. So for an engine with a 183* thermostat any temp up to somewhere around 203* would be perfectly normal.
red_stapler said:This is why cars don't have temperature gauges anymore.
I upvoted this, but it still bears repeating.
dps214 said:Sonic said:When in traffic, the temp will climb up to the same set cooling fan set temp
So you're saying it won't do anything to improve the one actual complaint OP has, about temps rising while sitting still.
The "right" solution is to make the fans come on earlier, or give yourself the ability to override it. On mine, the A/C didn't work but did still kick the fans on, so that was convenient.
Yes, the temp won't go back to the tstat temp when at speed- which is when it's better to be up 20F for efficiency.
As for "right", 220F on a modern car isn't a problem at all. So you are just spending more energy spinning the fan (which has a measurable impact on fuel economy).
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