Could it be a tired water pump ?

 

I had experienced similar last year. Fresh off a complete new system from waterpump to radiator including fan clutch. The ac dryer compressor and switches were all just 3 years old as well. I had also changed the temp sensor so decided after changing out tstat and no change in results to get new fan clutch. I didn't have usual fan clutch issues but that was it.

Spend what you have to, it is important.

 

When you say you changed your thermostat did you do that before these issues arose or did you change the stat trying to fix the high running temps ?

Sometimes older low mile cars sit a lot and may need a good coolant flush , sediments form more from sitting than driving.

That said I have also had ( not on a sec) a fan clutch that looked and felt fine but just wasn't engaging enough to keep the engine cool,

Also I wouldn't trust any t-stat but a Mercedes one,

Saw your car on german day looked fresh ,tight and brite. Lucky man!

 

I had the same problem in my coupe after my rebuild and I replaced the Radiator and condenser because the fins get clogged with shit over the years. This is assuming all is well mechanically.

It can't get enough air passing through the fins. Also the tubes could be blocked too.

 

I suspect the T-stat. Reason is no change during highway driving, which usually does wonders on big engines to cool them...

 

Have you verified the aux fan is running, or are you just assuming it is? If it's not, could be the gauge just reads a little high. If you have an IR temperature sensor, aim it at the thermostat housing and take a reading.

 

Are you sure the AUX fan is running at BOTH speeds? Hi and Low?

 

Thanks all for your ideas & combined W126 wisdom...

Radiator: new BEHR

Coolant: New MB blue 50/50 mix

Aux fan: When the temp sensor is disconnected the fan spools up to full speed, connected it went back to 1/2 speed. It runs nearly all the time when engine is fully warmed. Loud as hell on full speed.

Thermostat: This was the first thing I changed in my quest for a lower coolant temperature. It made no difference from the original MB t/stat.

Water pump Today, in the 4th of July parade, I revved the engine to 1000 . 1200 rpm and this immediately brought the temp down a couple of degrees to the 100 mark. I have seen this over and over whilst sitting stationary with the A/C on for ten > fifteen mins the temps climbs a couple degrees only and can be brought down by revving engine ... It just goes up a small amount and stays there...

At road speed the temp will go down a drop when decelerating down a hill .. as I might expect...

MBL

 

This was the exact same thing that was happening in my coupe and when I changed out my condenser, that fixed it. The fins get clogged with shit over the years and restricts the airflow. I know its a bitch to change and you'll need a re-charge, but if my opinion means anything...

 

This was the exact same thing that was happening in my coupe and when I changed out my condenser, that fixed it. The fins get clogged with shit over the years and restricts the airflow. I know its a bitch to change and you'll need a re-charge, but if my opinion means anything...

I follow your logic completely Mike..

I had attempted to clear the condenser airflow using compressed air.. To take it to the next level, I shall try out some CRC [or like product] foaming condenser cleaner... See if that makes any difference at all... Funny thing is the fact I can see the radiator matrix whilst sighting through the condenser fins.. it really 'looks' pretty clear..

If I can find some of that stuff, I'll give the full report yay or nay later today..

Home Depot here I come! http://www.homedepot.com/p/AC-Safe-...aner-AC-921/206740351?MERCH=REC-_-PIPHorizontal1_rr-_-100664957-_-206740351-_-N

Mike, your W126 knowledge & opinions are valuable.. both to me & others who may come upon this thread in the future..

Thanks

MBL

 

Thermostat. Rated 80C means it starts opening at 80C. System is operating fine. If you want it to run cooler get a lower one...

 

I disagree. With an 80 C thermostat he shouldn't see temps higher than 85 or maybe 90.

 

Hi Interested All,


Sooo... I got da stuff at Home Depot this morning, got lost on the way to my time sensitive meeting, nearly got stopped for my custom europlate on the front.., and used the elixir thisafter when I got home...

No change

I am admittedly TOTALLY resistant to just chucking the SEC condenser & replacement of it.

So.. Mike... I am replacing the A/C compressor in the very near future... Part ordered etc.

At that time, I shall remove the condenser from the car & drive for a bit WITHOUT A/C !!!! to test your synopsis.

If different OK ... I spring for new one and like overnight ship..

Keep on truckin' man, ..... & thanks.

MBL

 

It does sound like it could be the condensor

Let us know what your test with it removed does

 

My '87 USA version 560 never had any of this...........

Such a price, Glamor!

MBL

 

I understand your logic, (Money) and I'm with ya, but that test does not really test the problem because the engine will not be under full load conditions, will it? But okay, do what you gotta do. It could give you an indicator.

Also, replace all of your belts at the same time. Ensure they are properly tensioned too.

Make sure the two driving the WP are matched too.

 

You say you can cause the temperature to drop by slightly by reving the motor, that makes me think clutch fan ,weak water pump or plugged passages in the block or heads.

 

You're kind of all over the place here pal. Are you guessing? Or do you know? You said T-stat, he has a new one. You said 80 degree, that makes zero difference. Now all this.

He said when he revs it the temp goes down. Says to me airflow. Says to me WP and fan clutch working. Says to me, old car and not enough air flow through the front end.

He's got a new Behr so we'll see when he does his test. I could be wrong? Have been before, but I went through this exact same issue with a brand new motor, and told him what fixed it.

And MBL, it prolly wouldn't kill you to do a CA flush either. Just don't leave it in too long. Read my thread on the WP install. I'll fix the pics in that one shortly.

 

I'll just chime in and mention that it takes a lot to eat up the water pump on these. Unlike most cars, which have a stamped steel impeller, these have one made of cast iron - less susceptible to corrosion and more efficient to boot. I've replaced the pumps on both my SEC and SEL, partly for peace of mind, although the SEL had some bearing noise. Both had MB pumps with no evidence of wear that would reduce flow (both were likely original, although it's hard to be sure). So, to my mind, the water pump should be the last thing you replace unless you've narrowed it down pretty well.

Ingrid has been running a little on the hot side too, so you're not the only one. Seems to average 90-95C, and it's topped 100 a couple times on really hot days (I've been seeing 80-100F for the last month). I need to address the airflow question, I haven't checked the fan clutch, and I'm sure the radiator and condenser could use a cleaning. So, more to-do for me there.

Lastly, higher compression doesn't cause higher coolant temperatures that I've ever heard of. If there are differences that make the 117.965 run hotter, it'd be things like coolant flow, not compression.

 

Did you ever do the infrared thermometer test ? My thought... a slightly incorrect temp gauge. Get a wrecking yard cluster and swap the cluster out to compare. $20 and a half hr. labor. My 300 SE gets to 92,95 on a 108 degree day, A/C on in town.

 

Unless you drive through locusts low mile cars generally don't have plugged condensers , old low mile cars that sit can develop sediment problems . I have had cars with fan clutches that looked fine but never locked up enough to cool an engine .

It's all guessing when you can't run diagnostics, so we all guess from past experience. Thats all that is possible on a forum .

 

Very strange problem. My high compression 420 motor has only done this when I needed a new radiator. It happened to both though, or really both already behaved this way when I got them. New radiator sorted both.

Temperature gauge sender can easily be faulty, but that should only affect the reading on the cluster.

 

Same problem thermostat jammed, changed that after changing the sensor. Fixed. Then what the heck , changed the radiator and hoses.

 

Yeah I wonder about that non MB thermostat you've used Malcolm. Do you think it could be worth testing it in hot water?

 

Richter Rox

When you say you changed your thermostat did you do that before these issues arose or did you change the stat trying to fix the high running temps ?

The thermostat was replaced along with the coolant as this would be the least expensive start in the diagnostic process. It made no change whatsoever in the coolant temp gauge readings...

Update: The warm running coolant temp has remained a constant all Summer regardless of the ambient air temperatures and whether or not the A/C is on. It is 100F (give or take half a smidge) whether prolonged idling or hours at highway speeds around 80 mph.

Before I am asked, Yes the aux fan runs.. and yes it has both speeds too..
Last month, I swapped out the Aux cooling fan assembly due to an unpleasant grinding sound from the fan motor...

Oh, also I can disconnect power to the Aux fan and get the same readings under the same circumstances of operation.

Still perplexed here...

MBL

 

Change the dash gauge. But first verify radiator temp. with a infrared temperature gun.

 

I have used a temp pistol on it and it seems pretty accurate..

I have yet to swap out the temp gauge itself.. and the gauge has been a constant throughout all this..

Thanks,

MBL

 

If the temp gun says the same temp as the gauge, then a slightly restricted radiator core could be your issue. Have you moved the gun over the radiator surface to ck for cool areas?

 

A new BEHR radiator was installed a month or so ago, replacing a slightly weeping one with no discernible internal blockage.

Hi ian & John: The original thermostat was replaced with a new Mahle Behr unit rated at 80C. Its design incorporates the bypass "foot". There was no change from the original one. I did look to test the old one. could not find.. Must have recycled it out...

At the same time, the coolant was replaced with blue G-48 antifreeze mixed to 50/50 ratio with distilled water.

A new MB coolant expansion tank & cap were installed as well.

Both temperature sensors located at the base of the top radiator hose were replaced. One was branded Mahle Behr, the other I do not remember.

MBL

 

it would be super simple and fast to swap sensors between your two cars. They are easily accessible on the intake by the thermostat housing. i had a no-op gauge that was just a bad sensor. I got a parts store unit and the car read over 100c. Installed a junkyard sensor and I'm reading right at the 90c line. its possible you just have a failing or incorrect sensor. You at least have a known good one so would be interesting to test.