Blocked Grill and Erroneous Temp Readings?

Shows you the blocked grill is helping.
It measures temp right in front of the center of the radiator.

 

And if you eveeeer get an engine block heater it gets weirder. Like when you know it's 0F outside and your Prius says 15F.

Wayne

 

I've noticed this behavior as well. Last week, there were a couple days where temps in the morning were around 0, and the prius consistently read around 9-10, even immediately upon starting the car.

 

Maybe Coastal Dave can come up with a blocked-radiator thermometer compensator :_>

 

Interesting, not that you say it I think I have seen the same. My temp has been like 4-6F higher then what I had expected. I hadn't made the connection until now, while frustrating I can live with it.

 

<div class='quotetop'>QUOTE(FireEngineer @ Feb 15 2007, 08:31 AM) [snapback]390804[/snapback]</div>

Right you are Wayne; my Prii was one that you made an install on last Saturday. We have an attached, unheated and minimally insulated garage. Still, this a.m., when it was about -4 in Madison, the Prius temp reading as I back out was 30 or 32 degrees. That was after the block heater had come on for about the preceding three hours. On our short commute (barely 5 miles), the Prius temp reading is still well above the actual outside temp but steadily dropping, of course. I'm anxious to see how my mpg average increases over a few tanks with the use of the block heater. I can only get the benefit for the short commute into work since the ramp where I park doesn't provide outlets :lol: but it's still going to make a difference. Can't thank you, your son and Ken enough for making the installs for several us last weekend.

Jim

 

Good observation. I had upper grille blocked and temp. reading was pretty close to what radio reported. But since I blocked 1/2 lower grill last weekend I also have been about +5 what real temp. is. I got my block heater today so it goes in Saturday. I think I can get it in OK but have to review threads for best cable routing.

 

Tony

Nope, I never noticed any weird temp-delta with my grille blocked. For example, if my digital thermometer with outdoor probe on the balcony claimed -36 C, my car claimed -33 C. Comparing ground level to higher up, that's close enough for me

However, what I *did* notice, was a general delay in reporting temperature changes. For example: driving in off the street into the underground parking. I know for a fact the heat is usually kept around +15 C or so, yet I can sit there for a couple of minutes and the display will claim -25 C or whatever it was when I drove down.

Same as when I leave the underground parking. The temp will claim +14 C or a similar value, and it can sometimes take 3 blocks before I get the Snowflake, then a couple more blocks before it gets close to what it should be.

Actually I thought it was just me, that the heavy drinking was finally taking a toll. Happy to see others are experiencing it. Or perhaps they're also the tragic result of heavy drinking ... beats me

j

 

If the upper and lower grill is completely blocked then the engine compartment will hold some heat. The temperature is measured just inside the compartment so will give a high reading when the engine is warm. I found it to be a problem when I have been parked for a short time, the gauge would give me a false reading - too high. The downside is that you may not get an ice warning, and on a mild day you might think it is too hot and unblock the grill. I decided to leave the two far ends of the lower grill unblocked, that allows some air flow over the temperature probe. One end would do the trick but it looks a bit odd. I haven't seen a noticable drop in mpg since doing this.

 

Rather than start a new thread I thought I would bump this one in light of the fact that the cold weather is coming on quickly around these parts. I have an 08. I installed an EBH. I blocked the grill. I have a 2 mile commute and I am hoping this will help.

My question is this - where exactly is the temperature probe located? I would like to open it up a bit in that area but I'm not sure what is what in behind there.

 

It's located on the lock support post that's runs vertically under the hood latch. It's about half way down the support, opposite the horn. You will have to remove the black plastic radiator cover to reach it. If you look at my "I acquired a project vehicle" thread there are some pics with the bumper off were you can see it.

 

If you're driving around now with a blocked grill I hope you have a Scangauge II or something else to monitor coolant temps.! With ambient temps of 20C or about 70F you will start to get the Prius coolant up above 90C. It won't boil until around 120C, but just a warning. I suspect in Vermont you can get 80F days in September.
I'm currently running with just the upper grill blocked. I'll block the lower one in a few weeks, when 20C days aren't expected (it's 24C today and wonderful!).

 

It makes perfect sense that you are seeing this. You've effectively added lag to the temperature sensor response by decreasing air flow across it. In addition a bias has been created because the air space is relatively dead and will be impacted by internal sources.

I doubt it is a problem unless the temp is going into some ECU calcs.

I've had to fix/compensate for similar issues in process equipment, especially reactors where lag or bias were very bad things... Had one with a poorly designed thermowell/thermocouple in a dead elbow of pipe. This resulted in really nasty cycling during changes in reactor operation. Redesigned all three parts to insert thinner thermowell directly into flow. This improved response by two orders of magnitude from minutes to seconds. It was a lot easier to run the reactor after that.

Not having looked at where the sensor is myself, my first thought as a quick workaround is to unblock a strip directly in front of the sensor. That should allow some air flow directly past the sensor while still accomplishing most of what is desired in blocking the grill.

 

"It's located on the lock support post that's runs vertically under the hood latch."

This is just about in the middle of the lower grill, correct?

I don't have a gauge - BUT - I installed the block the other day just to get myself ready for the colder weather which is just around the corner for sure! I have a 2 mile commute so I'm not too concerned. I'll remove the block (or most of it) today before I do any real driving this weekend and then wait for the colder weather to block again. But now I'm pretty much set for winter.

While we are on this topic though. At what temp do you all think it is safe to drive on a hilly Interstate highway at 60mph with a fully blocked grill?

P.S. I was in Edmonton this summer for a couple of days on my way to and from Inuvik. Nice country.

 

I'm still not sure what that darn temp sensor looks like and exactly where it is. I want to unblock a bit right in front of it to get it some air. Could anyone point me to a picture that shows the sensor pretty clearly? I'm getting high outside temp readings. I saw the pictures in the project vehicle thread - but I'm not sure what the sensor looks like so I can't really find it.

Our temps are now much lower. Lows below freezing. The highs are in the low 50s. I have the grill fully blocked. Its working very well for my short commute. I am getting into stage 4 almost immediately it seems. I expect to see a FE improvement. I may even start plugging in at the office before I head home in the evening.

I do not have a gauge. I know - I should have one with a blocked grill. But, until I scrape together the spare dough, am I ok running a fully blocked grill in 50 degrees or under. I'm not worried at all about the short commute. But I do often take runs on an interstate - I never exceed 65, usually 55. In your experience - no warranties express or implied of course - do you think I have anything to worry about assuming these conditions?

 

I'm pretty sure that sensor is only used to display the outside temp on the MFD, so it won't impact the engine operation if it's reading incorrectly. It's mounted on the vertical strut that supports the hood latch.

A -fully- blocked grill will trap -some- heat but once you start driving it very quickly reaches ambient in my experience. Now I do have openings in each side of my grill block so YMMV.

In my case it is actually safe to drive in +25C temps with a "fully blocked" grill. Pics. of my blocking are on this site. I drove on the highway with ambient temps of +29-30C (confirmed with an indoor/outdoor thermometer in the car) and coolant ran around +95C. Still very safe. I don't think the Prius system will boil until you get above 120C.