lost my fan/water pump belt today .. dumb question of the day - PeachParts Mercedes-Benz Forum

mabbonizio · #1 01-11-2018, 07:44 PM

Driving home tonight my fan belt let go. I guess I should have pulled over as soon as the battery and two brake lights came on but didn't as I wasn't in an opportune spot and honestly thought it was an electrical gremlin.

I glanced at the temp gauge and noticed it climbing steadily and pulled over right when it was at around 115°C and shut the car off. Temp rose to right under 120 (never went into the red mark) and I changed the belt on the side of the road.

What was odd was that in the time it took me to change the belt in the dark (had a spare in the trunk) the motor had already cooled down to 60°C in about 35 mins.

Is it possible I damaged the engine getting it that hot? Part of me says the system is designed to operate within the range of the gauge. The neurotic part of me says, 30 year old cooling system and head gasket may not operate well at almost 120° C...

There was no steam and I opened the rad and the coolant level was right where it should be.

Diseasel300 · #2 01-11-2018, 07:51 PM

If that's all it got up to, you're probably fine. If the ambient temperature was already cold and/or windy and the engine hadn't been driven long enough to get the oil hot, cooling off that quickly isn't abnormal. One of the benefits of an engine-driven fan is that when the belt lets go, the fan freewheeling in the breeze coming through the radiator will still circulate some coolant through the engine.

Any idea what took the belt out? Was it just old, or did it fail catastrophically? Recheck your tension in a couple days and make sure you aren't too loose or too tight.

mabbonizio · #3 01-11-2018, 08:00 PM

Quote:

Originally Posted by Diseasel300

If that's all it got up to, you're probably fine. If the ambient temperature was already cold and/or windy and the engine hadn't been driven long enough to get the oil hot, cooling off that quickly isn't abnormal. One of the benefits of an engine-driven fan is that when the belt lets go, the fan freewheeling in the breeze coming through the radiator will still circulate some coolant through the engine.

Any idea what took the belt out? Was it just old, or did it fail catastrophically? Recheck your tension in a couple days and make sure you aren't too loose or too tight.

Funny thing is the motor was at operating temp for a good 35 mins and had been climbing a slow hill... it is 50° here tho..

The reason I'm annoyed is because I think I'm the reason the belt went out

I was checking the fluids earlier this afternoon and noticed the belt was a *smidge* loose so i tightened it. I guess I made it too tight because it started chirping about 40 mins into my drive earlier, I thought it was because I had driven through a big puddle so I just ignored it.

CDTurbo001 · #4 01-11-2018, 09:30 PM

You'd have to have a healthy belt *really* dang tight to cause its failure that quickly. It may have been about to go and the extra tension finished it off.

If this is a 123 we're talking about... why didn't it have two on it?

mabbonizio · #5 01-11-2018, 10:29 PM

Quote:

Originally Posted by CDTurbo001

You'd have to have a healthy belt *really* dang tight to cause its failure that quickly. It may have been about to go and the extra tension finished it off.

If this is a 123 we're talking about... why didn't it have two on it?

my 240 only has one fan belt?

ESchwab · #6 01-11-2018, 11:17 PM

Quote:

Originally Posted by mabbonizio

What was odd was that in the time it took me to change the belt in the dark (had a spare in the trunk) the motor had already cooled down to 60°C in about 35 mins.

There was no steam and I opened the rad and the coolant level was right where it should be.

When your fan belt broke, the coolant stopped circulating very effectively. That meant that the coolant in the motor got really hot while elsewhere in the cooling system the coolant was at a lower temperature. The heat probably spread out in the system during the 35 minutes.

CDTurbo001 · #7 01-11-2018, 11:36 PM

Quote:

Originally Posted by mabbonizio

my 240 only has one fan belt?

Oh - you didn't specify the model and I was going on my 300CD which has two V belts running over the crank/water pump/alternator, with a dedicated belt to the PS pump and another to the A/C compressor.

chrisgt · #8 01-12-2018, 08:28 AM

I wouldn't worry about it, that's not too hot. It's also normal for the temp to rise after the engine is shut off. When the coolant flow stops, heat from the head and cylinders heatsoak the coolant and the temp rises above what it was operating at, sometimes by a significant amount. The temp sensor is on the side of the cylinder coolant jacket, so it's going to see a good amount of heatsoak. If I shut my car off after a long drive with the temp around 80C or 90C, then start it back up five minutes later, sometimes it's over 100, but comes down fairly quickly once it starts circulating.

xaliscomex · #9 01-13-2018, 02:09 PM

Quote:

Originally Posted by mabbonizio

Driving home tonight my fan belt let go. I guess I should have pulled over as soon as the battery and two brake lights came on but didn't as I wasn't in an opportune spot and honestly thought it was an electrical gremlin.

I glanced at the temp gauge and noticed it climbing steadily and pulled over right when it was at around 115°C and shut the car off. Temp rose to right under 120 (never went into the red mark) and I changed the belt on the side of the road.

What was odd was that in the time it took me to change the belt in the dark (had a spare in the trunk) the motor had already cooled down to 60°C in about 35 mins.

Is it possible I damaged the engine getting it that hot? Part of me says the system is designed to operate within the range of the gauge. The neurotic part of me says, 30 year old cooling system and head gasket may not operate well at almost 120° C...

There was no steam and I opened the rad and the coolant level was right where it should be.

Belts came off my 1979 300sd (w116) twice and car overheated to the red mark both times. On one of the those times the alternator belt severed the tranny line. Car survived and I have not experienced any more problems. DO NOT USE the gauge to tension the belts "Cricket". They are not reliable. I used the gauge both times. Use your thumb or fingers. Just tighten them good but not too tight and you will have no problems.

BillGrissom · #10 01-13-2018, 08:12 PM

In my 300D's, the red mark is at 120 C, and that is just a warning. Yours saw only 115 C, so no worries. I lost both fan belts in my 1985 300D one evening driving to class, after a piece of metal popped up off the freeway (or perhaps one was already missing and didn't notice). Drove home 10 mi after class and temp never rose over 110 C, so doubt I hurt the engine. Was ~50 F that evening. My wife probably did worse by filling it w/ gas and driving 4 miles home.