Loose belts cause high temps? - PeachParts Mercedes-Benz Forum

acastell · #1 10-25-2004, 09:44 AM

I just purchased an 84 300TD in San Diego. I flew down and drive it back to San Francisco on Friday. The car is a 9 out of 10 in every area...I really got lucky!

The only issue that I have is the running temperature. The temp guage is between 97 and 102 always, depending on load. I read all of the posts and was comforted that many feel high 90s, providing the neede does not go apst 102 and I am not loosing coolant, is OK.

I myself like the car to sit in the low to mid 80s. So, out to the garage I went with a few possible 'general' problems:
1) Bad thermstat
3) Clogged cooling system
3) Bad temp guage

So, I drained and rinsed the radiator, removed the thermostat, then added Citric Acid cleaner.

With the thermo out, I let the car idle. I hypothesis was that is the temps rise beyond ~60, with thermo out and full flow of coolant, then I may have a 'clog' in the cooling system. Well, after 15 min of idle, the needle barely moved. So, I decided to go for a drive (I know, not recommended by some, by I had testing to do)

I drove 12 miles, 7 on the freeway, climded a latge grade, at speed and the rest high rev on a back road. The temp guage never scared 80, probably got to 60 at the peak of the large grade. So I concluded:

1) The temp guage is working
2) There are not clogs in th cooling system, WITHOUT the t stat.

So, I figured that the t stat was stuck on a partially open position that held the temps around 97.

So, installed a new MBZ t stat and darn it, SAME restults.

1 conclsion:

I must have installed a faulty t stat. And, ironically, it is stuck open in the exact same postion as the old one, wow, call ripleys.

My knowledgable friend who helped with the coolant flush, actually, I helped him, noticed that the belt were loose. I am not sure which belts, but his comment was, 'wow, I am surprised your alternator is charging. So, the belt that goes to the alternator. My AC is ice cold if that matters.

As we sat there amazed that we found two tstats with exactly the same tolerances, he then said:

Dangit, your belts are loose and that is why you are running hot. The fan is not turning. Moreover, the installed tstat, even though it may not have a function with a fan that will not turn, has just enough resitance to keep the temps at 100ish, letting just enough coolant through.

So, in your grand wisdom, is he right. If we tighten the belts, might the temps drop? Does the Alt/fan belt have anything to do with the AC, because this works TOO well, ice cold!

Thank you for making it this far into the post and thank you in advance is you have enough energy to respond!

AC

whunter · #2 10-25-2004, 09:57 AM

Quote:

Originally Posted by acastell

My knowledgable friend who helped with the coolant flush, actually, I helped him, noticed that the belt were loose. I am not sure which belts, but his comment was, 'wow, I am surprised your alternator is charging. So, the belt that goes to the alternator. My AC is ice cold if that matters.

As we sat there amazed that we found two tstats with exactly the same tolerances, he then said:
Dangit, your belts are loose and that is why you are running hot. The fan is not turning. Moreover, the installed tstat, even though it may not have a function with a fan that will not turn, has just enough resitance to keep the temps at 100ish, letting just enough coolant through.
So, in your grand wisdom, is he right. If we tighten the belts, might the temps drop? Does the Alt/fan belt have anything to do with the AC, because this works TOO well, ice cold!
Thank you for making it this far into the post and thank you in advance is you have enough energy to respond!
AC

The fan must turn, the back side is the water pump = no blow = no flow on most engines.

KCampbell · #3 10-25-2004, 11:59 AM

A/C is a different belt than Alternator and water pump/fan, so nothing inconsistent there.

If the belts slip the fan won't turn as fast and the water pump won't pump as fast. I believe that your engine is like mine, two belts for the alternator/water pump, one for the A/C and one for the power steering pump.

Rather than theorise too much, I'd be tempted to just tighten the belts to the correct tension and see what happens. Take a good look at the belts for signs of cracking, it might not be a bad idea to just replace them all. I just did this job last weekend with a new set of Gates belts from NAPA, they were all in stock and total cost was around $40 from memory. My old belts were in bad shape, the NAPA (Gates) belts look to be very good quality.

Kevin

Pete Burton · #4 10-25-2004, 12:12 PM

Loose belts are a great thing to find because they are so simple to adjust or replace.
The correct continental belts which fit properly can be had off Fastlane cheap.
Do a search on fans to determine if yours is in good shape, but definitely start with the belts.
If they've been loose for a long time they may be glazed, replace them if they are, otherwise you'll need excessive tension to prevent slipping.

acastell · #5 10-25-2004, 01:31 PM

Thank you all...

I will tackle this in a few days...

AC

acastell · #6 10-25-2004, 07:40 PM

Well, I took the car to the local shop. They felt the tension of the belts and all agreed that these were todally within spec. At idle, the fan spins fine. When RPMs are increase, the fan spins faster. So, this does not appear to the the problem.

We did reinstall the t-stat, with the arrow pointing straight up. I did not know about this nuance. After install, the car appears to run a bit cooler. I have yet to see 100, stays right around 90-95. Still too high for my taste, especially with an 80 degree t-stat.

The needle on the guage is acting strange. On one of the test drives, the needle seemed to jump, not move, but jump between 95 and 100.

We then let the car idle for about 30 min to clear any air bubbles....I just drove the car for 40 miles and the temp guage was steady, no jumping. But, still too high, 95ish.

Any ideas...

AC

Lycoming-8 · #7 10-25-2004, 11:17 PM

These 20 something year old temp gauges are not always right on the mark. See if you can get someone to check several spots on your cooling system with a non-contact pyrometer, infrared temp gauge, or some similar instrument. It may just be the gauge itself. Also the jumping needle could be a faulty ground problem and that could affect the steady state reading as well.

acastell · #8 10-26-2004, 12:45 PM

I would like to test the ground but that would require I remove the dash cluster, I think. This is beyond my experience level.

Could the sender be the culprit? I read in the archives that a faulty sender can cause the needle to jump a bit. BUT, will it also cause the gauge to read high.

I did have the tech take IR temp at the top radiator hose. Reading was 72 and the temp gauge was at 95. The prompted my tech to tell me that there were no issues and just drive the car.

Still, I have to have a good temp indicator...I am obsessed with watching this.

Is the sender easy to install..I know where it is as the tech pulled it off and sure enough the gauge dropped to zero.

AC

Pete Burton · #9 10-26-2004, 12:59 PM

If you really want to test the sender, you can do the following: Remove sender and clamp one end of an alligator clip test lead to the threads of the sender, the other end to a good ground. With the sender wire attached, put the sender in a pan standing up, with a meat or candy thermometer near it with probe at the bottom of the pan. Pour boiling water halfway up the sender. Turn ignition on and observe. If the thermometer and dash unit agree as the water cools, it's OK. Otherwise, it may be time for a new sender.

acastell · #10 10-26-2004, 01:28 PM

Good advice, but I think I am again past my abilities to do this. A new sender at MBZ is $24. Is this is a simple install, I do not mind spending the money.

Has anyone ever installed one?

AC

acastell · #11 10-26-2004, 04:57 PM

Well I went to the dealer to buy a sender. The guy behind the counter, sensing my furstration, asked me to describe the problem so he could run it by a Tech!!!! Great service...

The Tech said that it is most likely the Potentiometer or the gauge and he recommeded against buying the sender.

On the drive home from the dealer, I stopped by the indy. He has an IR Temp gun. My temp gauge was at 95, steady. He shot the upper hose, block, sender area and all the reading were between 69-74 degrees. He removed my resevior tank cap and NO AIR released. He said the engine is running at a very nice temp, no problems with the cooling system.

So, I have to dig out the Instrument cluster and dig out the gauge and look around. Problem is, I have never removed the dash and I do not know what to look for. There is a shop that will, for ~250, take my car for a day and look at the Potentiaometer as well as fix the gauge, if broken.

Not sure what to do...if I can live with the faulty gauge, then I should shut up and drive according to my Indy.

Anyone been in this postion?

AC

Pete Burton · #12 10-26-2004, 05:10 PM

you said the gage drops to 0 with the wire disconnected. I assume shorting the wire to groung causes it to peg. Thus, the gage reads lower with increasing resistance? If this is the case, what happens when you install a small resistor in series? The temp should read lower, right?

acastell · #13 10-26-2004, 07:13 PM

Pete, I really do appreciate your responses. I, however, am a very bad student when it comes to electical stuff...I am not sure how to ground and not sure how to install a resistor in series.

If you are asking the last question of me, then I have no idea how to answer. But yes, the needle drops to 0 when I pull off the sensor (take away current). So, I assume the opposite is true if I add current...

AC

bullwinkle · #14 10-26-2004, 07:29 PM

my '82 is the exact same (97-100C) with a brand new radiator, hoses, and Zerex GO-5 antifreeze(and new fluid in the fan clutch TOO!)-if you do a search on this topic you will find that anything below 120C is considered "normal" for these cars-like yours, at 100C I have fairly low pressure in the top hose and it feels hot, but not enough to burn you. I would think that with a quality coolant mix, a tight cooling system w/a good pressure cap, that even 120C wouldn't do any harm(occasionally)-248 deg.Fahrenheit.

whunter · #15 10-26-2004, 07:59 PM

Take the car to your local repair shop.
Have them install an aftermarket temperature gauge.
I saw a nice one attached to the driver A pillar last week.

I will not drive a Mercedes that reads over 100C, unless I am carrying a IR temperature gun.
An aftermarket temperature gauge is $6.80 to $118.00 = cheap to insturmentation quality.
80 - 90C is normal in the midwest..
In the mountains brief 100 + on a hard climb = Baker grade or grape vine, out west.