Radiator Temperature

[Mainer]

I have a 2005 Prius with 47,000 miles. I had noticed that on cold days that the engine took a very long time to warm up so I figured I better do something to help it achieve operating range.
I purchased a ScanGauge II from the Prius store and installed it. Set the unit to monitor the water temperature and was very surprised at the low readings I got. Read some tips from the groups here and then blocked off the top 3 slots in the grill. Not much change so I then plugged the top of the grill section below the top 3 leaving the rest below open.
After installing the foam in the grill at highway speeds of 55-60 the best reading I achieved was 170 degrees. At in town driving the temp dropped to 155-160. Outside ambient temp was 28 degrees. I also noticed that the temp varied greatly depending upon the road speed of the car. I have used the scan feature of the ScanGuage and have not recovered any codes at all. I am wondering if this is a normal thing with the factory thermostat or I do indeed have a erratic thermostat. Any suggestions or help would be appreciated.
TIA
Mainer

[DaveinOlyWA]

temp fluctuations are very normal. i block ALL the grill and at 28º F you should be too. in fact i block the entire grill all the way up to 50.

but the engine temp is going to jump around based on how cold it is outside and what kind of driving you are doing. normal temps for me first thing in the morning in winter usually just above freezing. i can take off, driving at street speeds bet 35-40 mph, heat up to 175º turn on heat, and temps will drop down to 165. stop at a light, i will drop another 10º. leave the heat on and i have seen it drop down as low as 135-140.

so, i pulse the heat for the first part of the trip to help heat up the Pri and keep it warm, but unless jumping on the freeway (even here, your car can cool off, just not as much) it will always be a struggle maintaining any real warmth.

Saturday, did a trip of around 30 miles one way, mostly freeway...with heat running most of the time, water temps were ranging bet 180-192 or so. turn it off and temps would peak around 200-201º

today, temps were in low 50's so never turned on the heat at all and did same trip. water temps ran from 200-204... so you can see what a difference running the heat can make.

had a PCD participant who brought some higher rated thermostats and i hope to get mine installed sometime this week, hopefully the will see some progress towards keeping the car warmer longer

[patsparks]

I have one of them "hot" thermostats. I was driving with the standard thermostat in 48 degrees Celsius ambient and coolant temperature went only to 90 degrees but it was flat terrain. Theory is that once the thermostat opens it shouldn't put any additional heat load on the system, with the scangauge I can keep an eye on it.

[DaveinOlyWA]

well i got one because 80% of the driving on the Pri is done at suburban speeds bet 35 or 40 mph. makes it tough to pulse/glide AND keep engine warm especially when temps are in the 30's and 40's F.

if the thermostat opens at a higher temp, its jus that much farther it has to go before i have to turn off heat to allow engine to warm back up (this creates CONSTANT "discussions" with SO who prefers to have it very warm...heck she wears hoodies (long sleeved hooded sweatshirts or zip-ups year round)

which leads to biggest reason why my mileage sucks during winter so much... she is normally the primary driver since i take Zenn....now mileage on most recent tank is good but only because we were on vacation for a large part where I WAS DOING THE DRIVING, otherwise the numbers would be 2-3 mpg lower

[halpos4]

I just received and installed my Scangauge yesterday for one reason in particular..Water Temp,and my question is..At what temperature would it be deemed critical,that the thermostat had failed and the engine was overheating?

[DaveinOlyWA]

oh, i wouldnt worry about it at the very least until you get to 212ºF. i can say for certain, i block 100% of my radiator up until the OAT is 50+F and i have never seen anything above 208

[halpos4]

Originally Posted by DaveinOlyWA

oh, i wouldnt worry about it at the very least until you get to 212ºF. i can say for certain, i block 100% of my radiator up until the OAT is 50+F and i have never seen anything above 208

Cheers Dave!!

[JimN]

Originally Posted by halpos4

I just received and installed my Scangauge yesterday for one reason in particular..Water Temp,and my question is..At what temperature would it be deemed critical,that the thermostat had failed and the engine was overheating?

A fan should activate to provide cooling. In over a year of having the grill blocked to some percentage my fan has yet to turn on. The highest temp I've seen on the Scangauge is ~190.

[halpos4]

Originally Posted by JimN

A fan should activate to provide cooling. In over a year of having the grill blocked to some percentage my fan has yet to turn on. The highest temp I've seen on the Scangauge is ~190.

It's good to know from these post what temps can be regarded as normal operating temps,recently a fellow Taxi driver with 220,000mls+ on his 04[without a ScanGauge] had a head gasket blown,thermostat failed.......Expensive!!

[Oddest_raindrop]

From personal playing.... I found that on cold mornings with temps in the any where from -10F to 20F you can have the prius warm up to 175F with the heater in the car of except for a brief period to keep the windows clear. Driving 55mph you can easily bring the water temp down to 130F once the car warms up and stops pulling heat out fo the car you can bring it bake up to 190's while still going in the 55 to 60 mph range. This is with all but bottom most grill openings blocked. going slower you start to get less heat and it can go down.