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1978 280slc
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Discussion Starter #1
I changed the thermostat and it should be the right one but the car is running hot. I didn't completely drain the system so I think air might be somewhere especially because the coolant has actually expanded since I added it, which shouldn't happen. Does anyone know of a decent way to burp the system after the coolant is added? If it turns out to be a pain I'll drain the car completely and refill it correctly so no bubbles are present.

Any tips or tricks would be appreciated. Hopefully the thermostat isn't bad, but there really isn't anything to it except a copper spring. I got 15$ of fresh coolant so I have to save the stuff.

Thanks for the help folks!
 

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'80 500SE AMG '80 300SD '78 450SLC '00 Passat GLX Wagon
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I think if you do a search in the W116 forum for threads I started there is one about the same problem when the thermostat was changed in my SD. Should be the same setup- I seem to remember something about the top rad hose and parking on an incline or something.
 

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1978 280slc
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Discussion Starter #3
I may have come across what you're talking about, I'm going to let the car cool down, drain it and open up the thermostat housing to make sure it is position correctly, never know what could be the problem. The belt was loose yesterday, but the car still seems to run too high especially after I changed the thermostat.

I'll keep y'all posted on what happens.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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I may have come across what you're talking about, I'm going to let the car cool down, drain it and open up the thermostat housing to make sure it is position correctly, never know what could be the problem. The belt was loose yesterday, but the car still seems to run too high especially after I changed the thermostat.

I'll keep y'all posted on what happens.
What's "hot" ? You should have a 87C thermostat for your M110.
 

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89 300ce, 85 380sl Euro
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Take the small hose on top of the radiator off, fill the tank till water(coolant) comes out of the port. Reconnect the hose. Turn the car on with heater set to max heat, run till operating temp is reached, shut off the engine let it cool down and top off the tank.
 

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1978 280slc
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Discussion Starter #6
Will do, thanks for the reply. Fill it through the overflow vent, makes more sense than going through the radiator neck by far.

My car was running way to hot talking 100C down hill so something is definitely off. The thermostat I got is 87C and I checked and it's the right one. I must have screwed something up when I filled the system. I guess it's part of the learning process. The original thermostat was quite an oyster if I must say so myself. I've cracked hard oyster and now I can crack a thermostat.

Hopefully all goes well and I'll comment how stupid I am! Thanks for the help folks!
 

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1973 450 SL
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1,126 Posts
I have a similar problem with my 73 SL. Running the freeway at about 80mph for about 15 miles, came to my turn off which is a couple of miles from home and just before I got to my drive the high speed fan cut in (what a noisy thing that is). Anyway the temp was just above 225F, probably half way between 225 and red line.

My problem is that I haven't gotten around to getting a service manual for the car yet so don't even know where the thermostat would be. Scott mentioned the location verbally, but I still can't figure it out. Anyone with a picture?

Remember I am still new to all of this, and in fact have never wrenced a car before. Been working on the body and interior mostly and now is time to learn about the drive train.

Loren
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I have a similar problem with my 73 SL. Running the freeway at about 80mph for about 15 miles, came to my turn off which is a couple of miles from home and just before I got to my drive the high speed fan cut in (what a noisy thing that is). Anyway the temp was just above 225F, probably half way between 225 and red line.

My problem is that I haven't gotten around to getting a service manual for the car yet so don't even know where the thermostat would be. Scott mentioned the location verbally, but I still can't figure it out. Anyone with a picture?

Remember I am still new to all of this, and in fact have never wrenced a car before. Been working on the body and interior mostly and now is time to learn about the drive train.

Loren
Loren - Those temperatures seem high for your car. The temperature needle on my car is at about 8 o'clock when hot and at most horizontal - about 180-200F. Later cars run somewhat hotter, but not the older cars. There is a problem in that there are different theromostats for the diferent 107s and we need the lower temperature one (I forget the temperature rating, but have it somewhere)

Locate the large hose in the front of the engine that goes from the rad to the engine. Look below where it connects to engine - that is the water pump. Look on LH side of pump facing engine and you will see another hose. It is attached to a nozzle that bolts onto the water pump with 3 screws - The thermostat is inside that fitting. Or so I am led to believe - I have never taken mine out!
 

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1978 280slc
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Discussion Starter #9
Follow the top radiator hose to the head, look in an automotive book It's not hard to find. Aluminum box thing on top of the water pump(has pulley) with a big hose going into it. I don't know where it's at on your car, but I don't think they're too hard to find. I have the chiltons manual and it is halfway decent depending on what you have to do but has no torque specs or anything like that.

Good luck!
 

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1973 450 SL
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So I have to assume that it's in the housing below my Water Temp Sending Unit.



Rather interesting. That sending unit doesn't look like an OEM unit. The plug that connects to the unit has 2 notches in it which I would assume would fit over two protrusions in the sending unit, which don't exist. Just curious.

I took her out for a bit of a run - Outside temp 75 degrees - about an hour in town traffic the temp stayed at about 190 degrees or 88C. I then took her out on the freeway for about 8 miles at 75 mph and the temp started to rise. It went up to about 205 to 210 (95 to 100C). Seems to be ok there. What I got from it is that the engine does heat up more at higher speeds than just running around town.

Any comments?

Loren
 

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1980 450SL & 1988 560SL
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Mine does that too. I'm afraid to run my AC on the highway. At 70 mph mine ran about 1/8 below the red. The pointer was past level towards the hot side. I can back off to about 60-65 and it will drop to a level 9 oclock position. I did a double flush last fall and have a 39% antifreeze mixture according to my refractometer.
 

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2010 Mercury Milan Hybrid, 1993 BMW 325i convertible
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Rather interesting. That sending unit doesn't look like an OEM unit. The plug that connects to the unit has 2 notches in it which I would assume would fit over two protrusions in the sending unit, which don't exist. Just curious.
That looks just like the sending unit (it's actually the aux fan switch) that I replaced on my sister's 75, back when it was my 75, and that I just bought to replace on my 78. Bought them both from my local MB dealer.

I took her out for a bit of a run - Outside temp 75 degrees - about an hour in town traffic the temp stayed at about 190 degrees or 88C. I then took her out on the freeway for about 8 miles at 75 mph and the temp started to rise. It went up to about 205 to 210 (95 to 100C). Seems to be ok there. What I got from it is that the engine does heat up more at higher speeds than just running around town.
It's running warmer than it should at that temperature, although it does run warmer at high speed.

I wouldn't do this, because the speed limit is 65, but I have a friend with a 78 450SL that has made 100+ mile runs at 85-90 mph and his car doesn't get above 95C unless it's a VERY hot day - over 100F. Runs through the desert around Vegas (110F+) still keep it hovering around the 100C mark at a continuous 80 mph with the AC on. Since I - I mean 'he' - flushed the system and replaced the fan clutch, anyway.
 

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1978 280slc
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Discussion Starter #13
I replaced the fan clutch and think that was a waste of 140$. I kept the old one though.

Tomorrow or sunday I'm going to drain the system and check that the thermostat is seated well then refill and see what happens. It doesn't look like the system is getting pressure so I might need to tighten something down.
 

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1973 450 SL
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I think I will start by replacing the thermostat and see what happens, then perhaps a complete flush and go from there.

The only mechanical problems that remain at this time are.

- Runs hot at high speed.
- One of the injector hoses is leaking fuel. Will be replacing all.
- Small amount of fluid leaks from the diff and tran (very small)
- Not sure about this one? I know nothing about suspension but I have aftermarket shocks on the front (KYB Gas-A-Just shock absorbers) and I noticed that one side of the car is 3/4" lower than the other. I then measured the length of the front shocks from the bottom of the shocks to where the top and bottom halves meet and see that there is a 3/4" difference between the 2 sides. Are these adjustable, or should I simply replace them with bilstein? Perhaps it's something else. Not sure.

Loren
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I think I will start by replacing the thermostat and see what happens, then perhaps a complete flush and go from there.

The only mechanical problems that remain at this time are.

- Runs hot at high speed.
- One of the injector hoses is leaking fuel. Will be replacing all.
- Small amount of fluid leaks from the diff and tran (very small)
- Not sure about this one? I know nothing about suspension but I have aftermarket shocks on the front (KYB Gas-A-Just shock absorbers) and I noticed that one side of the car is 3/4" lower than the other. I then measured the length of the front shocks from the bottom of the shocks to where the top and bottom halves meet and see that there is a 3/4" difference between the 2 sides. Are these adjustable, or should I simply replace them with bilstein? Perhaps it's something else. Not sure.

Loren
Loren,
Re hot running, this is what I would look at if it was my car:
- Thermostat should be 75C for an early SL like yours and 80C for late models.
- Aftermarket water pumps often don't put out full flow - best to use MB rebuilt unit if your's has been changed.
- Incorrect timing (insufficient advance) can cause high temperatures. For my car (and yours) timing should be set to 30deg BTDC at 3000rpm with no vacuum. (At same time make sure mechanical advance and vacuum retard are working properly.)
- Have cooling system flushed and cleaned properly.
- Make sure belts are tight.
My car used to run very hot, but after exhaust manifold cracked for 3rd time, the guy I went to to replace it was an MB expert and I think he reset timing.

I changed injector hoses about 10 yrs ago - just bought a length of metric tubing and proper clamps from MB. There is a kit, but way too pricey.

Don't know much about front suspension - Could it be that springs are different? Would shocks cause car to not sit level?

Those CO level were low - hot running probably helps with emissions and that is likely why newer cars are designed to run hotter.

Have your hot start problems gone away - how did you resolve them?
 

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1973 450 SL
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Thanks, Graham

The hot start problems have gone away. Probably partially due to the fact that for the past 20 years this car was used an average of 1000 miles per year. Put some additive in the tank (don't know what it was now), and all is good.

Belts are tight.
Cooling system flush is in sight.
Timing has been adjusted by my service tech.
The pump is the original.
Will be changing the Thermostat to a 75 degree unit.

Once I get the collector status on the car and get rid of the hot running, perhaps the CO levels will rise, but at that point it doesn't really matter because I have the emissions testing done, and so long as I own the car I don't have to have it done again.

We will see what can be resolved in the next couple of weeks. New top and visors to be installed on the week of the 9th.

Loren
 

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2010 Mercury Milan Hybrid, 1993 BMW 325i convertible
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I have aftermarket shocks on the front (KYB Gas-A-Just shock absorbers) and I noticed that one side of the car is 3/4" lower than the other.
Shocks have very little to do with ride height. I'd be very surprised if changing the shocks had any effect.

If your car hasn't had the suspension rebuilt within the last 5-10 years, that's where I'd look first. It's also possible you've got a weak spring on one side, but the rubber is the big thing. You can check the spring height (or have it checked) at the same time the suspension is being rebuilt.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Thanks, Graham

The hot start problems have gone away. Probably partially due to the fact that for the past 20 years this car was used an average of 1000 miles per year. Put some additive in the tank (don't know what it was now), and all is good.
It could also be because you now have summer gas - the problems with vapour locking would only be with winter gas with high vapour pressure.

Timing has been adjusted by my service tech.
Do you know what he set it to? The specs in the manual are based on meeting emission controls, not getting the car to run cool. The figures I gave you are the ones used in Europe and by owners wanting their cars to run cool!
 

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1973 450 SL
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Scott, when you say "rebuild the suspension", that sounds like a very costly venture. Any time I see "Rebuild" I get this horrid feeling! I have such limited knowledge about any of this stuff.

What is involved? Would I do just the front or all the way around?

When your talking about the "Rubber", what are you referring to?

Graham, the hot start problem went away when we were still getting winter gas.

"Timing", no, I have no idea what he did, but will be questioning them.

This car is so close to completion that I am tempted to just take it to my mechanics and say - Fix It! By that I mean suspension, injector problems, fluid leaks and anything else that comes up between now and when I take it in.

I love the car and everything about it, but these (little?) things are driving me crazy. I know, "welcome to the world of owning a 35 year old 107".

Loren
 

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2010 Mercury Milan Hybrid, 1993 BMW 325i convertible
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Scott, when you say "rebuild the suspension", that sounds like a very costly venture. Any time I see "Rebuild" I get this horrid feeling! I have such limited knowledge about any of this stuff.
I don't know how handy you are - or want to be - but I got all the parts to rebuild the suspension for about $500. I did my 78 first and it was over several weekends. On the 75 I did it all in one weekend. The only part I decided I'll never do again is replacing the lower control arm bushings. It's tough to get the spring compressed safely and I don't have the tools for it. The local alignment place did it for me for $100 labor cost, I gave them the parts I already had. The rest of it is pretty straight forward. The first set of tools I bought was a 1/2" drive socket set and that got me through all the suspension stuff. Before my 78 I'd never looked at suspension in my life. Once I got under there and saw how things went together, there wasn't that much to it. You do have to get it aligned after - no option on that. I replaced front and rear subframe bushings, lower control arm bushings, upper control arms (it's easier to replace the arm than to replace just the bushings and costs about the same) sway bar bushings and mount rubber, tie rods and the drag link bushings.

Without a doubt, rebuilding the suspension was the best and biggest improvement in the car. I couldn't believe how much difference in made, both in ride and handling quality. It gave me enough confidence that I'm going to get a real spring compressor and replace the rear springs and rubber spring beds and I'm not worried about it.
 
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