I'm trying to figure out what the ideal operating temp is for engine coolant. What is normal according to Toyota for these 3rd gens?

188-194

While you're here, do you have any thoughts on running a 170 degree thermostat on a supercharged 4runner?

I don't have a supercharger and I'm running a Stant 170 degree thermostat. My opinion is, they don't do shit in reality. Yes, the thermostat opens sooner, but very quickly, the engine will get up to its operating temp anyway. Once it's open, it's open, just like the OEM thermostats that open at 180 degrees. It will keep the engine cooler in some circumstances, like driving down a mountain pass with no load on the engine, but that situation is never a concern. It's when you're driving in hot ambient temps and driving up a grade that you want your cooling system to be performing well so you don't overheat your engine.

The next time I'm due for a coolant renewal, I'm going to ditch the 170 degree thermostat because it's doing nothing for me.

Do you run an OBD-II tool like a Scangauge or Ultragauge? If not, you can monitor engine coolant temps, transmission temp, etc. and they are great to have. Are you having some overheating issues currently?


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I have a supercharged 4runner and i'm debating the pros/cons of running a 170 vs 180 stat. With the 170 i run at around 175 average temp...never going beyond 185 even when climbing crazy hills and i'm trying to figure out if that's optimal for my engine....especially during winters when it drops below 170... Is it good to run the engine at 175 all the time? Or is it better if it was running at 185... Questions questions...

I have a bluetooth obd that i use with torque

The main difference is that it seems to run things 10 degrees cooler on average. Is that something good? It definitely helps give the system a headstart when climbing passes but that's primarily a function of your radiator/cooling system. My main concern is during the winter....the system is now running at say 165 170.....are we accelerating wear n tear because the engine isn't at the intended operating temps?

Well I will add that I am not supercharged and therefore do not feel qualified to comment on the subject. I am interested to hear Tim’s take on this however.

I would think that having your engine operating at lower than standard operating temps could possibly accelerate wear, yes. That isn’t something I’ve ever given much thought to. I think less heat is better but to what point is the question.


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I've had a different experience than you with that 170 degree thermostat. Like I stated above, the thermostat opens sooner, but then it's open, just like the OEM thermostat does at 180 degrees. For both thermostats, the engine will eventually get up to operating temp, which is around 188-194.

I've never ran as cool as you are with the 170 degree thermostat. What brand thermostat are you using? Maybe the one you're using opens up further and allows better flow. If it does that, then it would make sense that it allows additional cooling benefits.

Running too cool isn't optimal for engine lubrication and I know certain engine functions rely on input from the coolant temp sensor but I don't know if running 10 degrees cooler would affect any of those systems.

I would run the normal thermostat. You want the engine to run at its optical block temperature..

However, if you want 170 thermostat, go for it. It's your rig do as you wish.

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I'm running a corolla oem thermostat thats a 170 degree one. It's the same size/fit as the 4runner 180 oem....just seems to run 10 degrees cooler. My usual operating temp (here in socal with around 75-80 degree weather is 170-180. If i'm going downhill...it drops to 172 or so....and if i'm going uphill 180....but on average its 175...

I've heard (but not read) the FSM says normal operating range is 175-205. If that's true, then this is on the lower range and if i go into colder weather, it will be running at 165 prob...

I know trd offered a 160 stat at one point for supercharged engines...i'm assuming that would run at 165 or so on average... But i think for supercharged engines, there is always the issue of ping and so perhaps thats why the cooler stat is recommended...dunno

Agreed.

Low temp thermostats are good for a bit of power (if you can tune for it!!!) for short bursts of power requirements - drag racing, quick street hits, short road racing time trials, etc. It won't help for long grades, high ambient temps, etc. if the rest of the cooling system isn't up to snuff.

In the case of a supercharged 5vz, it MAY help (with pinging and/or max power), but shouldn't be required. I see no reason to do it on an unmodified 5vz.

-Charlie

I have the 170 thermostat and am also supercharged. I'll throw in my .02 cents as well.

You are correct that in the summer it doesn't do squat when it's 90+ degrees outside with the A/C on. It fully opens sooner but will still run between 195-210 degrees, 210 being a very hot day in stop and go city driving.

In the winter it's a lot different. Because ambient air temperatures can be as much as 140 degrees cooler than the engine coolant where I live, I will often see 165 degree temperatures when going 70 MPH on the freeway on a rainy/snowy day. Does it create any sort of extra wear on the engine? I highly doubt it. This is a 5VZ-FE we are talking about and Toyota purposely overbuilt it to make it a strong engine. But that extra cooling headroom creates a lot more cooling capacity when I do some spirited driving and full throttle pulls from stopsigns and stoplights. If that is what you are after, then put one in. If none of that is applicable or desirable, keep the stock temperature one.

Now transmission temperatures are a whole other story and need to be addressed if you live in a hot climate and are supercharged.

That's interesting. I put in an OEM corolla thermostat (9091603107) and it doesn't go over 190 even if i'm really flooring it up a mountain on a 85 degree day. The average temps thus far (fall weather 75-80 daily) is 175....dropping to 170 on a descent at highway speed and going up to 180 when i'm climbing a gentle hill. I get a feeling this corolla 170 stat behaves a bit differently than the non-oems that are being used by everyone else...

On an 85 degree day yes I see similar readings. I don't watch my temps as much now that I got rid of my electric fan but before I did. Once it creeps over 90 and above the temperature increases in a linear fashion if the A/C is on. If no A/C then it stays a lot cooler. The condenser is right in front of the radiator so it will heat up the air before it passes through the radiator and reduces the cooling ability.

Where I live we see 108-110 several times a year so it gets a bit hotter.