Under bonnet EXTREMELY hot but temp reads fine on dash - Mercedes Benz SLK Forum

SLK R170 General Discussion SLK 200, SLK 230K, SLK 320, SLK32 AMG

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#1 Old 08-15-2015
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Under bonnet EXTREMELY hot but temp reads fine on dash

The other day I was standing outside talking to a friend while my car was running. I leaned up against my car and about burned my booty off! I took a look at the temp guage inside my car and it was very slight (maybe a needles width) above the exact center line. I popped my hood and EVERYTHING under the bonnet was too hot to touch. You could feel the heat coming out from a couple feet away. I checked my coolant level and it was right at the "minimum" mark in the overflow tank (I didn't see any "maximum" line marking. I drove home and popped the hood. Waited a good 30 minutes and everything was still quite warm and the engine itself was still so hot that I could only touch it for a second or two. I touched the hoses connected to the radiator and found something interesting. The top part of my lower radiator hose was still pretty toasty, but just below the little clamp that holds the hose in place about midway down it, it wasn't even hardly warm. The farther down I followed that hose, the cooler it got. Could my engine be overheating but the temp on the dash guage read OK? Maybe a stuck thermostat?
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#2 Old 08-15-2015
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Depends how long the car idled it takes a little while before the thermostat will open if you still have the problem after about 15 min. than i would say yes replace it.
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#3 Old 08-15-2015
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hey red dogs,i have a C55 AMG and the under bonnet temp is just the same.its a big mill motor and its fine
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#4 Old 08-15-2015
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Thanks for the replies and the reassurance! It had idled for about 20 minutes. I never heard the fan come on either. But I guess the coolant temp needs to get pretty hot for that to happen? I was at about 85-90 degrees Celsius. It was just alarming because it felt SO hot to my rear LOL. And then feeling how hot everything else was under there too seemed a bit unusual. Man, all those parts, electrical wires, etc. have to be able to withstand a lot more heat than I realized. Is there a "max" line for the coolant overflow? I've been thinking of doing a coolant flush eventually.
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#5 Old 08-15-2015
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Do you have insulation on the bottom of your hood? A hood pad. That should keep the hood cooler. 85-90C is hot, almost 200 F.
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#6 Old 08-15-2015
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Quote:
Originally Posted by ichris93 View Post
Do you have insulation on the bottom of your hood? A hood pad. That should keep the hood cooler. 85-90C is hot, almost 200 F.


Yes, I do have one. .
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#7 Old 08-16-2015
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The engine bay temps do run high on these cars. If your engine temp gauge is consistent, whether stopped at idle or with forward motion, you should be OK. You will notice a small rise in temp at idle, but that is not out of the ordinary. Just keep checking your vitals before you go and you should be good to go. If you have not replaced your coolant for some time, it may be a good idea to put in on your "to do" list.
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#8 Old 08-16-2015
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Thanks Jet! I'm not sure it's ever been changed. I've had it for almost a year and from the looks of the car when I got it, it's previous parent didn't spoil it. Temp is consistent, witjin the normal range on my guage, and like yiuvsaid, thete is a very slight rise in temp at idle but goes back down when going firwards. I'll be sure to add the coolant flush/replacement to my ever growing to-do list. I'll report back if that makes any difference once it's complete.
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#9 Old 08-16-2015
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Quote:
Originally Posted by 2_Big_Red_Dogs View Post
Thanks Jet! I'm not sure it's ever been changed. I've had it for almost a year and from the looks of the car when I got it, it's previous parent didn't spoil it. Temp is consistent, witjin the normal range on my guage, and like yiuvsaid, thete is a very slight rise in temp at idle but goes back down when going firwards. I'll be sure to add the coolant flush/replacement to my ever growing to-do list. I'll report back if that makes any difference once it's complete.
What color is the coolant?
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#10 Old 08-17-2015
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I'm shining a light into the overflow in one of the pictures, so I think that dramatizes the color a bit, but you get the idea.


EDIT: Actual picture as posted doesn't look as dramatic as it looked on my phone. This picture is probably close to actual representation of the color.
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#11 Old 08-19-2015
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Cannot tell that much. When you change it, use Zerex G-05, it is clear.
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