by "BJohnson11" (brettjohnson01)
Published 04/16/2017 at 21:52
by "BJohnson11" (brettjohnson01)
Published 04/16/2017 at 21:52
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So to give you all some background, when I first got the 300d, the coolant was kinda brownish and gross. The water pump housing eventually started leaking, so I took it in and had the housing, pump and thermostat replaced and the coolant flushed.
Ever since then, the coolant temp has seemed wonky. Before all that, the temp gauge would stick right around 85 to 90 deg C (the marks on the gauge are 60-80-100-120, with 120 being the overheat temp). After the work, the gauge will behave semi erratically. Some days it’ll stick around 90 deg C for my 40-60 minute commute, some days it’ll hover closer to the 100C mark (usually like, 97?). It’ll never overheat, and it never crosses that 100C mark. Then most days it’ll do a combination of the two, kind of fluctuating back and forth between 85C and 95C. Now, most of this isn’t too concerning, but it is a little annoying.
Onto the troubleshooting; my gut tells me its just a faulty thermostat, but I’m not positive. If I turn on the heater, the coolant temp will drop which implies coolant isn’t being circulated properly? No coolant in oil, but the coolant does have some brown liquid in it. Doesn’t seem like oil though because it’s always separated, I’m more thinking that at some point the Mercedes stock coolant isn’t the green stuff that it was filled with, and the difference in color is just the remnants of the old coolant. I’ve burped the cooling system a few times and I’ve gotten some bubbles out, but it seems pretty well bled. I asked my mechanic about headgasket and he didn’t think that was it.
Any thoughts?
"bob and john" (bobandjohn)
04/16/2017 at 21:57, STARS: 1
replace thermostat, stuff might be leaking by that,.
then flush it again and burp it right, go from there.
"V8Demon - Prefers Autos for drag racing. Fite me!" (v8demon)
04/16/2017 at 22:13, STARS: 0
Got any access to an infrared thermometer???
"Full of the sound of the Gran Fury, signifying nothing." (granfury)
04/16/2017 at 22:19, STARS: 0
Did you get all of the air out of the system? I know that on the E34 I would have to take some extra time to make sure that all air pockets were worked out otherwise the temp gauge would read erratically. The Vanagon was another story altogether, with the need to elevate the front of the vehicle to bleed it due to the length of the coolant lines.
Usually if a thermostat fails on a German car it will fail in the open position, and thus it takes forever to get up to operating temp, if it ever does. That’s certainly better than the alternative, where a failed thermostat leads to instant overheating.
"HammerheadFistpunch" (hammerheadfistpunch)
04/16/2017 at 22:20, STARS: 0
My guess is air at the top of the heating coil. Sometimes you have to cycle the heater alot to clear any trapped air during burping
"BJohnson11" (brettjohnson01)
04/16/2017 at 22:27, STARS: 0
So what would that burping process look like? Wait till it’s warm, blast the heater and open the coolant cap?
"BJohnson11" (brettjohnson01)
04/16/2017 at 22:29, STARS: 0
That’s kinda what I initially thought but I spent a week where every day after I got home I would burp the system and it had no real change. Coolant level didn’t really seem to change either. But it is a popular theory for erratic temp readings so maybe I’ll keep at it.
Agreed on the thermostat point (more likely to fail open) but a quick easy replacement I suppose.
"BJohnson11" (brettjohnson01)
04/16/2017 at 22:30, STARS: 0
Not at home but at work. What are you thinking?
"Full of the sound of the Gran Fury, signifying nothing." (granfury)
04/16/2017 at 22:32, STARS: 0
See if you can elevate the front of the vehicle so that the fill point is the highest point in the system and leave it open while the engine is running. Be sure to turn on the heater as well. Those are the things that I had to do to finally get the E34 to cool reliably.
"BJohnson11" (brettjohnson01)
04/16/2017 at 22:33, STARS: 2
Ok, that has been my process to this point sans the elevation, so I’ll try that. Thanks!
"V8Demon - Prefers Autos for drag racing. Fite me!" (v8demon)
04/16/2017 at 22:38, STARS: 0
It will let you know if the gauge is accurate for one. Always make sure your reference point, in this case the gauge, is correct.
I had a thermostat issue last year. Car wasn’t really putting heat out.... Believe it or not, it wouldn’t open fully. It opened when it was supposed to, but took until about 210 to open a little more than halfway. This was a 180°F thermostat. The one I replaced it with was FULLY open @ 184°F.
"BJohnson11" (brettjohnson01)
04/16/2017 at 22:44, STARS: 0
That’s kind of the intuition I have with this one. What are you aiming the ir gun at to prove temp?
"V8Demon - Prefers Autos for drag racing. Fite me!" (v8demon)
04/16/2017 at 22:48, STARS: 0
Housing, inlet side of rad, outlet side of rad. Take note of all 3.
Any variables change when the gauge reads higher? Heat/AirCon/defroster on? Ambient air temp? Heck, headlights? Some clusters have a voltage regulator on the backside that does WONDERFUL things when it starts to go....
"BJohnson11" (brettjohnson01)
04/16/2017 at 22:54, STARS: 0
Seems to be not too dependent on other variables. Turning the heat/defroster on will drop the temp but only for a limited time, which seems to be a function of the coolant in the heater core getting circulated around.
"V8Demon - Prefers Autos for drag racing. Fite me!" (v8demon)
04/16/2017 at 22:59, STARS: 0
I wouldn’t be too surprised if the gauge is of the bi-metal variety and just showing it’s age.
"BJohnson11" (brettjohnson01)
04/16/2017 at 23:02, STARS: 0
That’s also very likely. When I take the coolant tank cap off the coolant has never been hot to the touch, so overall I’m not that concerned. I think I’ll swap the thermostat, burp the system and troubleshoot from there.