Ok, so I filled the system from the upper hose, bled it multiple times, Behr 80 degree T-stat, filled with 50/50 distilled and proper coolant, car was running 80-85 consistently before the change. The housing was leaking so I figured I'd change the T-stat, now it runs 100 when it's cool, but today it got up to 115 with the a/c on! This is confirmed with an infrared temp gauge.

Radiator is clean, fan clutch works, it is bled properly, car ran cool before, am I blowing this out of proportion, is it simply a bad new thermostat? I've heard of that before, but never had a new bad one.

Now the weird thing is that when it read 115 at the cylinder head near the temp sender, the t-stat housing was 95 ish. I don't know if that's normal or not.

Heater brings temp down. Am I missing something?

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

sounds like the stat is holding temp too long. 95 to 100 is normal, but 115 is not.

why don't you put the original stat back in and see if the temps stabilize?

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Is the aux fan functioning properly? It's a thermo-switch controlled electric fan in front of the condensor. The switch measures the temp of the receiver dryer (behind right headlight) and kicks on when the R/D gets hot. The aux fan is NOT linked to the coolant temp circuit. There's a fuse, a fuse for the relay, a relay, some wiring, etc. So it's possible the aux fan may contribute to the higher temps.

Anecdotal observations from a half-dozen or so recent T-stat swaps reported online here for "higher temps" would support a general trend of increased temps after the swap. From the ubiquitous 80-85 pre-swap to 90-100 post-swap.

I recommend joining EPC startek to the get online access for the manuals. There's a good discussion in the Factory Service Manual (FSM) about how the bypass t-stat in the W123 is supposed to work.

It was not for a Mercedes but I got a bad new Thermostat last year; so it does happen.

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84 300D, 82 Volvo 244Gl Diesel

Aux fan works like a champ. Again, the car ran 80-85 before the t-stat and I had changed the coolant about 2 weeks ago, figured out the bleeding procedure and all that, I bled it 3 times to be sure.

The running 115 at the head and ~95 at the t-stat is what concerns me. I'm wondering if that's a normal difference between the two and the old t-stat was way cool, or if there is some blockage in the head and now it's showing it's ugly face... I tossed the old t-stat on trash day and drove it after pickup I've seen some 160 F degree ones, maybe I'll try that.

Thx for the input.

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

It seems to be more common now for threads to pop up regarding hot running after a new thermostat than was the case 6-7 years ago. It seems some of our go-to companies have begun to cut corners (Bosch, Febi, Meyle, Behr, etc) in the last few years, so given your problems I'd say it's definitely possible and probable. Just make sure the t-stat is installed in the proper orientation to elminate a reverse thermostat. Your car should run between 80-100c in most operating conditions, my rigs rarely get to 100c even with the A/C blasting in stop-and-go traffic on a 100f+ days, but that seems to be about the normal upper limit for my cars, so you're definitely running hot.

Some friends down the road have a european car shop, I'll check with them on that. Is that supposed to be a permanent fix?

I did read the common new t-stats run hotter after the fact, I wish I would have tested the old one for temp opening. I just figured it would be a preventative maintenance item, simple R&R... Lesson learned.

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

It was only 83 today and it was running that hot, while at speed too. I put the t-stat back in the same way and found the arrow and pointed it up. I'll do anything to fix a hot running car, it will be 115 degrees in about 4 months and old cars have to be in tip top to handle it around here.

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

I'd just try swapping out the thermostat for a new one. I remember a few years back I was in the Palm Springs area in July and it topped 123F one day, it was so hot the newer Caddy I was driving at the time just gave up and shut down at a light, the POS didn't even have a temp gauge or warning light, it just shut down after sitting for about a minute at those temps. I understand why you want to get everything in top running shape, those kinds of temperatures can bring all kinds of headaches, lucky for us, the older Mercedes are probably the most durable and reliable cars on the road so they can handle it if in good shape.

Thanks for the time guys, I did search some but it looks like I should have searched some more. I've read a lot of other possibilities. If someone finds this and doesn't like post whore's, I'm sorry!

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

It's not a fix, bypass is a graduated operation of the t-stat. A portion of the factory service manual (FSM) is in post 20 here: Thermostat holes?

At medium temps, some coolant "bypasses" the radiator in order to keep the engine warm. Above about 94, on a good t-stat, the bypass closes and all the coolant goes to the radiator.

T-stat installed correctly? It is possible to put them in backwards. There's also supposed to be an arrow pointing up. The book says "put the arrow up" but I don't think there's solid consensus why. Probably for bleeding air, but it's not clear how, since the t-stat is symmetrical.

I mentioned this in another post related to this subject, but I, too, have recently swapped a thermostat (water pump as well). Pre swap, I was running around 82C, post swap I'm at 90-95C, depending on the demand for heat via the climate control. But even running the car at highway speeds of 75-80 mph, the temp gauge never broke 100C, it stayed right at 95. I agree with thatguy (funny handle, btw), it would appear that more thermostats are turning up faulty.

Unfortunately, your engine seems to be running far too hot. 115C is an unsafe range, but that's an obvious statement. If you can afford to not drive the car for a bit, pull the t-stat and perform a boiling water test to see if it opens up properly. I suppose the other go to option is just exchange for another thermostat, but I don't know if that option would be contingent on proving the one you initially received was faulty. Depends where you got it and how good the customer service is. If you bought it from PeachParts, tell Phil what happened. He'll make it right.

__________________
Never be ashamed to ask for help.

1985 300D
1987 300SDL
1970 Jaguar E-Type OTS
2002 Dodge Intrepid (Traded In)
2011 Ford Crown Victoria

From above, sheesh, do people really put t-stat's in backwards? The same way is with the springs towards the block, and with the arrow the way the FSM calls for. UP...

Thx, I'll look into the bypass.

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

Thanks Tanks,

I bought it from Peach, it's a Behr. I won't drive it, I have an old derdge with a Cummins diesel that still works from time to time I'm tempted to buy one of these lower operating temp units due to the climate where I live (Arizona)...

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

That is never the correct approach.

I have noticed that as well. After an apparent "break-in" period, temps drop to the original level. But the "delta" has been on the order of 5-10 degrees C., not the 30 degrees that you report.

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