Coolant temp. How hot is too hot?

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mitsuman47

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Hello all. I have a 2005 honda civic with ~95k miles on it, and live in east texas. I got myself a scangauge II in feb. All through the spring and early summer (we've had a relatively cool summer) my coolant temp has stayed around 182-195F. Yesterday was the first hot day we've had, with temps getting close to 100F and high humidity. On an all highway trip to dallas I saw the coolant temp creep past 200F, then between the time I exited the highway and pulled into a parking garage it got to 213F!!! I guess my question is, is this normal? I didn't have the gauge last summer, so I don't know if the coolant got that hot. BTW, my coolant is at the max level and there are no coolant leaks under the car after it is parked.

Thanks for the help, and sorry for the noob question.
 
Sounds about normal if you are running the a/c. I'd change that coolant if you haven't or if it's been a long time. Be sure your underhood fan(s) are operational.

How does the scangauge temp reading compare with the dash gage?
 
Taking a wild stab I am certain that 2,800 degrees farenheit is definitely too hot.
 
Thanks for the help guys.

Yesterday, I was to recreate the scenario, and honestly it didn't take much. I think you are right about the fans MrCritical. With the a/c off, temps stay low at high speed, then go up at low speed. With a/c on, temps are low all the time. I have a fan that comes on only when the a/c is on. So I guess the "normal" fan is not working. I didn't have a chance to check it out this morning, as it was dark when I got to work, so I'll check it out this afternoon and report back.

I really hope this made sense.

MrCritical, with the exception of initial warm-up, the temp gauge on my car doesn't seem to deviate from its normal position, regardless of what the scangauge reads. Also, there are no numbers on the car's gauge at all.
 
Well 212* F is the standard boiling point of water (it can be lower or higher depending on altitude or barometric pressure). You add coolant to the water in the cooling system to increase the boiling point. I would suggest that you stay under 225* F (but there's no rhyme or reason to that number). Many temp sensors have a "sweet spot" in the middle range where anything in a 10*-15* range will register in the middle.

Assuming the temp gauge is working, just watch it and try to keep it from overheating. If the temp creeps up, then check the traditional problem areas (water pump, thermostat, radiator fan, coolant leak, head gasket...)
 
mitsuman, your temp can go above the termostat setting when you out run the cooling capacity of your radiator due to clogging.

One thing to watch for as you get up in miles is crud build-up in the radiator. Sometimes you can see it by looking at the tube ends inside the radiator with cap off. NEVER TAKE CAP OFF WHEN HOT>

To minimize this, radiator shops have recommended change fluid every two year(yea even the Dextron long life stuff), I drain but not flush then refill. Typically about 50% comes out. Check maintance records, if negelected suspect build-up.

But once crud is there I'm not sure the best way to improve.
I would talk to a radiator shop if you think you have a problem. I've done Prestone flushes which is fine for old fluid/not much crud but too much work for minor improvement IMO.

I had a neglected Range Rover, wife blew a hose & shop put on a new hose. Next day she over-heated it blew out heater core ($1200)and sucked in a valve ($2400). After valve job shop finds...oh the radiator needs to be rebuilt. This is why I do my own work.
 
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Bringing this sucker up from the dead...

So, since posting this in '07 I drove around thinking it was pretty much normal for my car to be running at 213f on hot days. Soon after, I actually saw 220-223f a few times and 227f once. I did a few drain and refills and nothing changed. Then the mailman showed up one day, and I had my answer.

Honda sent me a letter saying that I should bring my car in because the coolant may have been contaminated from the factory, and may be clogging up the radiator. So, by the time I left, they replaced the radiator, hoses, and coolant...for free!!!, and WAY out of warranty. Two thumbs up for honda. I'll be buying my next car from you guys.

I've been keeping a close eye on the temps, and even on a day that was in the high 80's the coolant temp never got above 182f on the scangauge. I used to see above 200 on a day in the high 70's, if I went any more than 30 miles down the highway. Now I'm interested in what the temps will be when it's 105 this summer...
 
Your fans probably don't come on till 220 or above so 200-213 is normal in summer time temps especially in stop and go traffic.
 
Thermostat ratings are the OPENING temperature of the thermostat.
they vary as to their fully open temps.
A 195F therm can be correct if it is fully open at 215, for example.
With proper coolant and pressure in the system, this is not a problem. it actually increases cruising efficiency for gas economy.
There is less loss of heat, and more for power - a small shift in this direction.
Ford had a dual temp thermostat - one setting for cruising, and another for full throttle power.

So 210 or more can be very normal.
 
Nothing to worry about, that engine is very easy on oil and you were cruising on the highway.

I have the service manual for the 2001-2005 Civic if you want/need any info about the cooling system for your car.
 
modern engines are designed and calibrated to run hot.

220 is not even excessive, actually a good thing.

The car is probably set up to run 200 as a minimum.
 
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