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1981 Mercedes 380sl
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6 Posts
Discussion Starter · #1 ·
New hoses, belts, water pump thermostat and running at about 100 degrees. Any ideas? This was at 100kph (60mph) 28 degrees Celsius outside. It stayed pretty constant at this but I’m planning a 200km (each way) run this weekend. Thoughts?
Speedometer Vehicle Gauge Car Steering part
 

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Outstanding Contributor , Bob's Your Uncle!
83 280 SL- 5 speed-The PIG
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33,760 Posts
#1...How was it behaving BEFORE all this was done?

#2...What thermostat was installed...degrees wise?

#3...Cooling system burped? Might be trapped air somewhere.
 

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1981 Mercedes 380sl
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6 Posts
Discussion Starter · #3 ·
#1 it’s new to me last fall and didn’t drive it until I had the work done.
#2&3, I’ll assume it’s the correct thermostat and that it was properly burped (reputable old school Benz mechanic) but I could be wrong. Thanks for laying down some clues.
 

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1973 MB 350 SL Euro 116 engine
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184 Posts
Do you own a laser thermometer?, you should, they are cheap and super useful for things like this, as well a hundreds of other things around the house. I think I saw one on sale in Canadian tire's flyer starting tomorrow, usually ~$20-$30.

Don't trust the dash gauge alone, get some real time readings from numerous spots on the engine and cooling system parts.
 

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Outstanding Contributor , Bob's Your Uncle!
83 280 SL- 5 speed-The PIG
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33,760 Posts
#1 it’s new to me last fall and didn’t drive it until I had the work done.
#2&3, I’ll assume it’s the correct thermostat and that it was properly burped (reputable old school Benz mechanic) but I could be wrong. Thanks for laying down some clues.
New to you so you have no idea. As Busdaddy said...try an alternate source of testing the heat generated.

Did the dash gauge temperature reading come down when you slowed down? Or at idle??
 

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1977 450 SEL 6.9
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949 Posts
Might be worthwhile to burp it again. Sometimes a lot of air gets trapped and it needs multiple burps. Also run the heater at max heat to purge air out of the heater core.
 

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Outstanding Contributor , Bob's Your Uncle!
83 280 SL- 5 speed-The PIG
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33,760 Posts
Just realized @Washopay is from Barrie, On. LOL. We spent 20 years there.

Just moved from there back to Quebec.

Where did you get the work done?
 

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1981 Mercedes 380sl
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6 Posts
Discussion Starter · #9 ·
I checked with thermal gun and the dash gauge reads true. It does cool down a bit at a slower speed (down to high 80s early 90s). Engaging the heater did nothing but cook my eggs :p. Rad fins are clean and straight. No serial number for the thermostat. Small world Nobby, we live in Allandale and I take it down to Luxury AutoSport in SCHOMBERG.
 

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Outstanding Contributor , Bob's Your Uncle!
83 280 SL- 5 speed-The PIG
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33,760 Posts
North Star Motors on the corner of Tiffin and Ferndale have a good rep.
I also used to go to a fella up in Orillia....he grew up working on these era cars....Tom Milligan 705-727-6199
I lived on Ward ave and Loon ave...near Huronia. Just left Barrie for good Feb 28
 

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1982 R107 380SL
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4 Posts
This exactly where my 380 ran temp wise, until I had to replace the radiator. Now its barley above 80c max, in the Texas heat.

Edit: I feel like I have responded to this before, or there another post with this problem?
 

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1981 Mercedes 380sl
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6 Posts
Discussion Starter · #12 ·
Alex at northstar used to work on my wagon (newer model) but turned his nose up on working on the 380 (which kinda pissed me off but perhaps he had a bad day). Thanks for the Orillia connection though. I like Ed in SCHOMBERG though - he tells me to hang around and ask questions while he works - and he really knows his way around. One last thing. Congratulations on getting out of Barrie. I’ve got 5 more years then I’m gone too. I feel like I’m living in Vaughan.
 

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3 Posts
Id say if you have that temperature gun, try it at several locations on the radiator wile its hot and idling...you may find the blockage if it is there...cool spots versus hot spots.
 

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Outstanding Contributor , Bob's Your Uncle!
83 280 SL- 5 speed-The PIG
Joined
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33,760 Posts
Alex at northstar used to work on my wagon (newer model) but turned his nose up on working on the 380 (which kinda pissed me off but perhaps he had a bad day). Thanks for the Orillia connection though. I like Ed in SCHOMBERG though - he tells me to hang around and ask questions while he works - and he really knows his way around. One last thing. Congratulations on getting out of Barrie. I’ve got 5 more years then I’m gone too. I feel like I’m living in Vaughan.
LOL...all the people in Vaughn sold their house for huge bucks and moved to Barrie for half the huge bucks. I had 2 houses side by side. Sold my primary in 2020 to a family from Vaughn. Sold my rental (primary for 18 months) to an Asian family...guess where from?



PS: Tom Milligan used to work for Alex 15 years ago.:)
 

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1981 Mercedes 380sl
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6 Posts
Discussion Starter · #16 ·
This exactly where my 380 ran temp wise, until I had to replace the radiator. Now its barley above 80c max, in the Texas heat.

Edit: I feel like I have responded to this before, or there another post with this problem?
Ya. I posted on FB too looking for feedback. Thanks for responding.
 

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1977 450 SEL 6.9
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949 Posts
How do
how do I “burp” it?
Run the motor from cold then as the gauge temp rises to thermostat opening temp you carefully open the cap of the expansion tank whilst holding pressure on the cap as you loosen it whilst keeping the motor running. Best to wear a heavy glove and also use a rag to buffer the coolant and air escaping. The idea is not to have coolant spew everywhere, it really is just a quick open/close motion to vent/burp the air.
 

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MBZ '85 380SL, RR '77 Silver Shadow II, MBZ '98 E300TD, BMW '02 E46
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589 Posts
Could be worse. Corrosion "could" be the cause, but the suggestion to purge the air from every nook and cranny is a good one. Easier done on an inclined driveway with the bonnet end pointed uphill but ramps will do in a pinch if you have a set. They aren't terribly expensive and double as an easier way to find your way under the car to service suspension bits and check for leaks without a 4 post lift. If replacing the unknown thermostat with a known 80 degree (I believe that's the proper one for most North American 380SLs) unit, the next step will be a descaling operation. Not much fun I'm afraid. The two ingredients, other than distilled water, are TSP 90 and citrus acid - both are dry powders. You'll be using approximately a kilo of TSP 90 and then roughly the same in citric acid with flushes in between. Driving the car will get the water pump spinning faster than it does at idle and at highway speeds and your current elevated but by no means dangerous temp levels, this is probably the best approach.

1) Remove thermostat (which you'll be doing to replace it and the coolant along with it as part of this process) and run water from mains through the engine block and radiator core until you observe no visible signs of remaining coolant.
2) Fill with distilled water and a kilo charge of TSP 90. Drive for 30 min, 50 kilometers or whichever comes first while observing the temps. With no thermostat in there, temps shouldn't be any higher than already were and we can positively rule out a thermostat fault (though they mostly stick open or stick closed, not half-open).
3) Flush with water from mains until the discharge is clean and clear and repeat previous step with TSP 90 once more with the same duration/distance and appropriate caution.
4) Drain the suds and run water from mains until no suds remain, then refill the radiator with a charge of a kilo of citric acid and distilled water. Once again, drive 30 min or 50 kilometers, whichever comes first and keep an eye on temps.
5) Flush with water from mains until the discharge is clean and clear and then repeat the previous step with citric acid for the same duration/distance and appropriate caution.
6) Final flush - by this point you've very probably seen your operating temperatures drop by several degrees (verified against a more accurate handheld infrared thermometer) and if so, wait a few days before you refill with distilled water and compatible antifreeze/lube/anticorrosion juice as you might unclog pinholes and trace fractures that could reveal themselves one or two days. If leaks are found, don't despair: small leaks are generally cured with leak stop products added to the water left in the radiator. Most require heat to activate, so you'll be driving 20-30 minutes once more to confirm to let the polymer compounds do what their going to do. If one go doesn't plug up the pinholes, try again and repeat the process. Near 100 success rate is achievable on the second try so long as the breach in the radiator is a pinhole or a few of them rather than a more serious crack or puncture.
7) Final flush to get all the cleaning products out until the discharge is clean and clear.
8) Install the new thermostat and seal, replace the coolant with the proper proportions of distilled water and antifreeze and if you feel adventurous an additive like Water Wetter which will modify the surface tension of the coolant in contact with hot coolant passages (smaller bubbles, effectively).

In any case, good luck. Hopefully a radiator flush and new thermostat will prove sufficient.
 

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1973 MB 350 SL Euro 116 engine
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184 Posts
Out of curiosity, where are the block drain plugs located?, I'm assuming on the lower sides near the back (RH one buried under the starter maybe?), I want to do a full flush, but haven't researched where to look for the plugs.
 
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