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  #31  
Old 07-21-2020, 12:30 PM
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Quote:
Originally Posted by jsb357 View Post
Coolant Temperature Gauge

Due to the pressurized cooling
system, the coolant only starts
boiling at a temperature of approx.
257° F (125° C) with an antifreezeblended
coolant fill protecting down to - 2 2 ° F
( - 3 0 ° C)

During severe operating conditions
and stop-and-go city traffic the
coolant temperature must rise to
red marking only.
yes, i see that in my owner's manual, and it is at least reassuring

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  #32  
Old 07-21-2020, 01:37 PM
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Originally Posted by roky View Post
we're here year round, this is our first summer, i went from 6000' to 8400, and noticed i was up around 110
Ok. Well 110 is certainly too high.

Quote:
with the infrared temp gun, i know that my 80c thermostat is opening around 85, as measured on the thermo body, so 90 operating temp on the gauge probably is normal for this thermostat
Well if the T stat is working as intended maybe some kind of blockage or maybe not enough water flowing thru the system. Maybe the water pump?

Quote:
my attitude now is i can live with it, but i'm going to take a shot at lowering the temp, with a citric acid flush -- i know that when i replaced the radiator in my old 6.2 diesel van, there was a dramatic drop in temp
I will be doing that as well when I replace my T-Stat and heater valve on the firewall. Mine is leaking when I use the heat - on the one or two days every few years around Jan 01st when there is a point to using it in Phoenix.

One thing I will do, and you might consider this yourself is to disconnect the heater and flush it seprately from the engine flush. Might be gunk in the heater core that you may be able to get rid of more effectively doing it seperately than just doing a straight engine flush.

- Peter.
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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S
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  #33  
Old 07-21-2020, 02:13 PM
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Since you have an IR thermometer, shoot the radiator for cool/cold spots, this indicates blocked areas. For a more accurate reading with the IR when checking the thermostat opening temp place a piece of electrical tape on the housing and use that as the IR target.

Good luck!!!
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  #34  
Old 07-21-2020, 02:51 PM
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Be aware that an infrared thermometer can only read non-reflective materials and the sample "spot" grows the further away you are from what you're measuring. If you are reading a shiny spot, or bare metal, expect to have readings that don't match reality. Ideally measure something dark or corroded from a close distance (<6") for the best results.
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  #35  
Old 07-21-2020, 03:22 PM
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Originally Posted by pj67coll View Post
Ok. Well 110 is certainly too high.



Well if the T stat is working as intended maybe some kind of blockage or maybe not enough water flowing thru the system. Maybe the water pump?



I will be doing that as well when I replace my T-Stat and heater valve on the firewall. Mine is leaking when I use the heat - on the one or two days every few years around Jan 01st when there is a point to using it in Phoenix.

One thing I will do, and you might consider this yourself is to disconnect the heater and flush it seprately from the engine flush. Might be gunk in the heater core that you may be able to get rid of more effectively doing it seperately than just doing a straight engine flush.

- Peter.
the thermostat i'm using is recent, but unfortunately i did not test it before installation -- when i drain the system for the flush, i will test it -- because yes, its opening, but how much? -- when i test the old stat in boiling water, its opening, but barely, and not at all like a video i found of a 240d stat being tested -- at 20c above its rating of 80c, say 100c, boiling, it should be fully open -- i'm not so sure it is -- that also could cause a blockage, imho.

have to wait until the weekend for the acid to arrive, then will proceed
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  #36  
Old 07-21-2020, 03:25 PM
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Quote:
Originally Posted by Diseasel300 View Post
Be aware that an infrared thermometer can only read non-reflective materials and the sample "spot" grows the further away you are from what you're measuring. If you are reading a shiny spot, or bare metal, expect to have readings that don't match reality. Ideally measure something dark or corroded from a close distance (<6") for the best results.
yes, i painted the stat housing flat black, and i'm up close to it -- also, i tested the accuracy of the infrared thermo
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  #37  
Old 07-21-2020, 05:30 PM
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Let us know how the citric flush goes.
Something I'd been curious about doing myself.
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  #38  
Old 07-21-2020, 05:33 PM
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will do -- before/after temps on the same test route
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  #39  
Old 07-23-2020, 10:49 PM
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had the cooling system apart when i removed the radiator today and drained the block -- did the citric acid flush first, but really, very little effect cause the system was very clean, no sludge, scale, so on this engine i don't see clogging as the culprit.
i am replacing the almost new stat with a Stant 13588, and this time i tested both in boiling water -- major difference in the degree of opening, so the one i had installed may have been not fully opening, i will install the stant
and after removing the radiator, found much debris between the rad and the ac condenser, and a repair someone had made with epoxy -- can't believe it held for years -- so a new rad is coming next week
so i won't know which issue was causing the hot temp -- but i will suggest, as you probably already know, that not all stats are created equal, and always test them before installing
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  #40  
Old 07-23-2020, 11:00 PM
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I just read down through this and was wondering if the stat was a higher temp rating. I also wondered if you downshifted on the hill? If you allow the rpm to fall too much the cooling fan will not cool the engine properly....sounds like you are on your way to getting it all tip top.
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  #41  
Old 07-24-2020, 12:18 AM
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The thermostat issue sucks.

I replaced one recently that failed after only a year and a half...

Did you complete the full citric flush as per the FSM (degreasing, etc)?
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  #42  
Old 07-24-2020, 08:13 AM
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Quote:
Originally Posted by t walgamuth View Post
I just read down through this and was wondering if the stat was a higher temp rating. I also wondered if you downshifted on the hill? If you allow the rpm to fall too much the cooling fan will not cool the engine properly....sounds like you are on your way to getting it all tip top.
both 80c rating, but different manufacturers -- also, the stant is NOS, off ebay, is a more robust construcftion, maybe they were made different in "the old days"? -- but not too old, cause made in china
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  #43  
Old 07-24-2020, 08:27 AM
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Originally Posted by Shern View Post
The thermostat issue sucks.

I replaced one recently that failed after only a year and a half...

Did you complete the full citric flush as per the FSM (degreasing, etc)?
yeah, its not that it wasn't opening, or was stuck open, its that one is twice the gap at 100c

yes, detergent, etc. -- but even before i owned it, this is one of those mercedes that came with the maintenance booklet, all the maintenance done meticulously -- it looked the same before and after the flush

still don't know what the temps will be, will know next week -- it is a very cheap rad, about $85 off ebay/amazon, new, but the company has good reviews - klimoto, i think -- and on a manual tranny 240d, is very easy to replace -- will let you know how it looks
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  #44  
Old 07-24-2020, 12:06 PM
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Originally Posted by roky View Post
yeah, its not that it wasn't opening, or was stuck open, its that one is twice the gap at 100c
Don't forget, the thermostat serves TWO purposes on these engines. One is to allow cool coolant in from the radiator, the other is to BLOCK the coolant bypass port. If the thermostat isn't opening correctly, it isn't blocking the coolant bypass port either. The result is a low intake of cool water from the radiator and excessive re-circulation of hot coolant from the block.

I went through this with the SL last year. Original 1983 stat was lazy and wanted to run 100C all the time. Bought a new stat from the dealer and threw it in. Worked for ONE DAY, then overheating again. I went through everything thinking that an OE stat couldn't possibly be bad that quick. Finally replaced it with a Wahler and tested both in boiling water. Wahler was wide open, OE replacement couldn't even slip a fingernail in the gap. Overheating solved.

Never assume that "New = Good" I learned that lesson.
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  #45  
Old 07-24-2020, 12:24 PM
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Originally Posted by Diseasel300 View Post
Never assume that "New = Good" I learned that lesson.
sounds exactly like what i just experienced

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