Coolant Temp: 200 to 195 quick...

Probably the thermostat fully opened up. The fans will usually kick on around 193-5. Surprised you saw 200. The only time I see that is if I am climbing a mountain road. You might also have an air lock (bubble) in the system.

 

I have some reason to believe that my fan kicks on at 202-204F. Normal running temperature seems to be 192F, though hypermiling and city traffic often cause it to fall lower.

 

Ken seems to think the fan threshold is higher too but there are two fans and I believe (but not certain) they are variable speed.
When I was climbing a mountain road (20-30mph) I had the window down and could hear the fan(s) running at low speed. At the time the temp was 193. Where it kicked off, I don't know.

 

It is hard to imagine one being in there unless you have had a servicing done. Did you have the intake manifold replaced?
In most cases the bubbles work their way out.

 

Other than keeping an eye on the coolant level, I wouldn't worry about it.

 

The coolant won't boil until it gets up around 240F. 200 is no problem. It's normal to see coolant temps fluctuate a lot. This is why most car manufacturers "desensitize" the gauges (if they put them in at all). It causes questions like this one from owners if they read the -true- temp. I watch the coolant temp climb as the car climbs a long hill. When the fans kick in the temp drops very quickly. With the thermostat fully open and the fans at high speed you can drive at high speed in 100+F temps with no problem, even with A/C on.

I believe the comment is "relax and watch the blinking lights".

 

Following is a partial copy of my post.
--------------------------------
The thermostat starts to open at 82C(180F) and fully opens at 95C(203F). Therefore, the ICE coolant temperature is ...
below 180F:blue zone: cold
180-203F:green zone: good and acceptable
203-208F:yellow zone: semi-overheat
above 208F:red zone: overheat

Ken@Japan

 

Yes, 200°F is perfectly normal while driving uphill in the 70s and 80s. You dropped to 195°F while driving downhill. Coolant and oil temps quickly respond to changes in engine load. When I take a highway exit, it drops to 189°F.

My 2012 Prius regularly hits a coolant temp of 199°F on hills. This is driving up the mild hills in OK, not truly steep hills. My 2009 Honda Civic Hybrid had very similar coolant temps. On a hot summer day, it would never exceed 201°F. It also had a 203°F thermostat that was never fully open according to the coolant temps experienced by the engine.

 

Great info, I was searching for data on when the Prius thermostat opens and here it is. Thanks Ken!!

 

So I have a 2012 Prius V w/ 185K miles that was just diagnosed with a head gasket problem. I opted for the engine swap instead of the head gasket replacement because the cost was half the price for a refurbished engine with new gaskets and refinished head and pistons. However, this all started because the coolant temp warning light came on going up hill. After getting the car back I am still hitting 199-203 on the freeway and 205-206 on the hills. After running some checks in maintenance mode I realized that the fans kick on at 203 and shut back off at 199-198.

I am assuming this is normal and these engines really do just run this hot. Can someone confirm?

 

Mine likes to run at 195F. It takes particularly hot conditions to push it up to 200+ and trigger the fan, and I hit that very infrequently. Though this is a cooler climate.

Mine is at 98k miles.

 

200F on a steep uphill is normal as are fast temperature changes. As little as 150f when waiting to 200f under hill climb loads.

I have a real snoozer 17 minute video here for the seriously disturbed. Raw data, no narration. Temp, speed and charging voltages are displayed.

The car had just been driven at highway speeds . The video starts after a ten minute Ready mode waiting period with the temp at 150f. It quickly rises while driving in a neighborhood. There are a couple of short stops in Park where you hear the door locks cycle.

Towards the end (4:18 to 6:00) it goes to 201 for a minute as we go up a steep grade. This is followed by another ~ ten min Ready wait state where the temp drops back to 158 around 16:58.

.

 

Thanks for the info. It is nice to know that high 190's and even mild 200's are not unusual. However, mine is usually running in 195-199 on standard roads and hitting 206 going up hills. I just wonder if it can handle going up a lengthy mtn road for 30-45mins without over heating now.

 

I think 205 might be the highest I've ever seen with my ScanGauge 2. I usually grill block until it's fairly solid in the 80's. I was looking at doing a new thermostat and they're apparently 180F. I see 193 or 195 and that's usually it. I think it opens right around there. I think you should really only be worrying if you see 220-230. I think I was told that's when heads start to warp and then you start burning coolant and eventually blow it up.