cali315

2004 clk500 130,000km

Currently it is very cold here in Ontario -5 to -10 Celsius.. Lately I've been noticing over the past few weeks my engine fan has been coming on at full speed.. Around 100 Celsius on the temp gauge. Now it is happening more often then I feel is should be.. The car even got up to just under 120 on the temp gauge. The fan stays on and once the temp drops to 80 it kicks back off.. I haven't been able to see a routine of how the engine temp increases. Sometime while sitting at a stop light it will hit 100 and the fans will kick on, sometime in the drive thru, sometime while driving.. (But usually I've been stopped at some point before that).

My question is what is causing this? Water pump? Thermostat being picky and sticking a bit? No leaks that I have found! Rad is new from previous owner (I've owned the car since May or June) oil change was done not long ago with 5W40. All seems fine except this issue.. *the fan hardly kicked on loud in the summer @ +30 Celsius weather*

I've searched everywhere and can't find anyone that resembles my problem! Any help would be great! I'm going to do a coolant flush and change the thermostat to start but would love to hear what you all have to say!

Thanks in advance

cali315

can anyone share some advice or input please!! racking my brain over this for a few days now.. today on my way home the car went almost straight to 100 Celsius which then the fan kicked on and brought the temp back down to 80.. but sure enough it increased back to 100 (while driving) and the fan stayed on longer.. I also noticed the Outside Temperature was showing +24 degrees Celsius.. when it was really -1... if anyone could share some input that would be greatly appreciated!

Yidney

Can't help, but Rodney will likely chime later. Give it time.

cali315

I appreciate the heads up! hopefully Rodney has some ideas!!

Rudeney

I am going to guess a bad thermostat, but it could also be a weak water pump or even a defective engine temperature sensor. I'd use and infrared thermometer to check the temp of the radiator to see if it matches the car's gauge. If so, then that rules out the coolant engine temperature sensor in which case I'd go ahead and replace the thermostat. On the M113 engine, it's fairly inexpensive and easy to do. If none of that is the problem, then replace the water pump (again, not terribly expensive or difficult).

Oh, and the outside temperature sensor has nothing to do with this - it's just for the convenience of knowing what it's like outside. Most likely, the probe, located in the right lower side of the bumper, near the fog light, is dislodged and near the radiator causing the erroneous reading.

cali315

Thank you very much for your input! The thermostat was just changed.. the upper rad hose is warm and the bottom is quite cold.. I'm assuming the rad could be plugged up causing this? It was doing this before the thermostat was replaced to I believe.. Could this be the water pump perhaps? If it's a weak water pump I would assume it's not circulating properly and with not enough pressure?

cali315

Well.. New thermostat in.. And the car is continuing to do the same thing.. And it still climbs past 100 slightly while the fans are going then will drop when the fans kick off.. Another question, should my upper rad hose be fairly stiff or soft? Lower rad hose seems to be warm which it should be so I guess that rules out a plugged rad? I'm absolutely stumped with this and hate the guessing game I'm playing right now.
Could the system not be pressurized properly? (From a faulty reservoir cap?) or could it in fact be the water pump is slowly dying? There are no leaks anywhere, no warning lights, no power loss or anything I can feel.. Is that a auxiliary pump by the coolant reservoir? Could that be the problem?

I don't know if this is just in my head.. Or should be happening for that matter... But when I pull in my driveway (which is on a downward slope) the engine temp seems to increase?

I'm quite afraid of overheating as I do not want to blow a head gasket!

Any more input is again truly appreciated!

Patton001

My first thoughts are radiator or pump. I worked on a mustang once that had never had a coolant change a lot of sediment had collected in the coolant passages not allowing the coolant to flow sufficiently to cool. This was an extreme case. Bottom line is you either need to start doing things like removing your radiator and getting it flushed or replacing it, checking your temp sensor or something. It is really difficult to diagnose a car that is running hot because it could be multiple items. I am assuming your oil looks okay and not showing signs of a head gasket leak.

cali315

thank you for the input! very much appreciated! I am starting to think the same.. unless the thermostat I put in today is junk..
a bit of an update.. car seemed not to bad after a short drive.. which now that I think of it really would have only reached operating temp. On my journey across town not to long ago the fans kicked on at 100, instead of a them kicking off and the temp dropping back down to 80 they stayed on.. which I knew was not good as the temp continued to creep.. I hit some traffic and the temp keeps creeping to 120.. I couldn't get pulled over as quick as I would have liked however, the temp stayed at 120 and I pulled over shut the car off. wait a bit, start it up to turn back towards home and the temp is steady at 100.. fan would kick on it would climb to about 110ish and then would drop to 100 and the fan would turn off..
could I have just replaced a faulty thermostat with one that may have been working?? with that being unknown, im down to either the water pump is toast (no leaking though) or its the rad.. which is supposed to be fairly new.


I got home turned off the car touched the upper rad hose and it was HOT!! so that seems like the thermostat is working? reach down and touch the lower rad hose.. its cold like ice cold. now I noticed there is a hose from the reservoir that the lower rad hose connects into and then into the engine? if im not mistaken.. the hose going into the engine is semi warm (only really near where it mounts on the engine) and the lower rad hose coming directly out of the rad is the "icicle" its very cold.. which still brings me to a rad or water pump correct?

cali315

** could I have just replaced a working thermostat with a faulty one** (since the temp is increasing quicker and holding higher)

Rudeney

Since you have a spare thermostat, you can easily check to see if that't the issue. Take the thermostat apart and alter it so it no longer has the ability to shut off the flow of coolant. This will mean the engine will take longer to reach operating temp, but now you know its open so any overheating is not the result of a stuck thermostat.

If it isn't the thermostat, my next thing would be to look at the water pump. A new one is $100 and it's an hour's work.

cali315

Hey Rodney, thank you again for your replies and input! I have spoke with a MB specialist around my area over the phone, mentioned my issue and right away he thought the water pump. I looked over the car again yesterday and noticed there was not pressure in the cooling system... The upper rad hose while the vehicle is on and at operating temp does not feel like there is pressure being built within. Would that result in a weak water pump? I have no other ideas, my oil is clean, my coolant is as well.. However I did notice the mechanic who I had flush my cooling system quick after the thermostat replacement put the "green" coolant in the vehicle.. Which will be getting flushed out right away as I would like to stick with the recommended coolant. I'm going to have a new water pump out in tomorrow.. Hoping this will be the end to this madness! I will give an update once that has been completed!
Thanks again!

Rudeney

Lack of pressure in the coolant hoses would point to a water pump problem. Given the price ($100) it's worth a try in this case to "throw a part at it". As for coolant, Xerex G-05 is usually easily obtained and meets the MB spec.

cali315

Yes I 100% agree with you! That's what I'm thinking at this point! It's worth a shot! Thank you for the info on the coolant! I will be sure to have a flush done and then filled with appropriate coolant!
Hoping all goes well and this solves the problem! Is the "book" time for water pump replacement 1 hour? I was told 3 hours.. By the "book" however, this was from a local mechanic not the MB specialist.

Rudeney

I checked ASRA (MBZ book) and it lists 2.4 hours. On the V8, you have to remove the engine suction fan, so that adds some time vs. the V6.

cali315

Yes that would make sense! Thank you again Rodney! Your help has been greatly appreciated! I'll send a post tomorrow and let you know what exactly it was!

cali315

Sorry for the late response.. After it took a while for the local MB specialist to get the car in.. It was a simple temp sensor.. New one has been installed and car is back to running great!!
Thanks again for all the input! Truly appreciated