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#1
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w123 lukewarm heat
Seems like my heat isn't as hot as usual. It's just lukewarm.
Coolant is good, hoses at monovalve hot, 12v when set to MAX cold, Monovalve seems to be working. I do have intermittent clicking from the CCU, i cleaned the contacts and it clicks less often. Most threads on heat are about a failed monovalve and no heat, what's up with luke warm heat?
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1984 300CD |
#2
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What is your engine temperature? Should be right around the 80C/175F marker after driving a few miles.
If it is significantly below that, your thermostat is probably stuck open and the engine can't heat up to optimal operating temperature - this is bad both for you and for the engine. Feeling the hoses won't tell you anything, the difference between 130 F and 175 F is hard to tell since both are painfully hot to a human.
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The OM 642/722.9 powered family Still going strong 2014 ML350 Bluetec (wife's DD) 2013 E350 Bluetec (my DD) both my kids cars went to junkyard in 2023 2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles) 2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles) 1998 E300DT sold to TimFreeh 1987 300TD sold to vstech |
#3
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Back flush the heater core and thoroughly bleed the cooling system with the front of the car raised above the rear and the heat on full blast. Run the engine at 2000 rpm until it settles at operating temp and the lower rad hose gets hot. Once that is done let the engine cool down, and check the coolant level.
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'84 190D 2.2 5MT (Red/Palomino) Current car. Love it! '85 190D 2.2 Auto *Cali* (Blue/Blue) *sold* http://badges.fuelly.com/images/sig-us/302601.png http://i959.photobucket.com/albums/a...0/sideview.png |
#4
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In my experience, when the coolant is low you won't feel much heat. It doesn't take much. My son was complaining, "heat doesn't work" in my 1985 300D when he came home last week. I had told him to check the coolant when he left a month ago since I had drawn it down to check the upper hose and knew it would drop a bit as air worked its way out, but he doesn't listen. I only needed to add ~1 cup to hit the full mark (using Evans Waterless) and the heat was much hotter then.
I have also seen the temperature read too high when there is an air pocket. I have used a HF IR gun to measure next to the temperature sensor in the head (goes to dash gage) and the reading agrees quite close w/ the gage. You can get one on sale for <$30 and they prove very useful.
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1984 & 1985 CA 300D's 1964 & 65 Mopar's - Valiant, Dart, Newport 1996 & 2002 Chrysler minivans |
#5
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Maybe nothing to do with the coolant. Could it be that some flap in the heater box is not operating correctly. Maybe the recirculate flap is not closing all the way? This time of year that would allow cold air into the mix would it not?
- 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 |
#6
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It could be a flap issue, but the worst case scenario failure is FULL heat and full defrost. It's a safety thing.
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'84 190D 2.2 5MT (Red/Palomino) Current car. Love it! '85 190D 2.2 Auto *Cali* (Blue/Blue) *sold* http://badges.fuelly.com/images/sig-us/302601.png http://i959.photobucket.com/albums/a...0/sideview.png |
#7
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Car runs at 100C... always has, runs fine. At one point I replaced the thermostat, same running temp.
Coolant is topped off, added a "cup" just so you couldn't say I told you so. Still luke warm!
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1984 300CD |
#8
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Is your auxiliary water pump working?
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2004 F150 4.6L -My Daily 2007 Volvo XC70 -Wife's Daily 1998 Ford F150 -Rear ended 1989 J-spec 420SEL -passed onto its new keeper 1982 BMW 733i -fixed and traded for the 420SEL 2003 Volvo V70 5 Speed -scrapped 1997 E290 Turbo Diesel Wagon -traded for above 1992 BMW 525i -traded in 1990 Silver 300TE -hated the M103 1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one 1979 Silver 300D "The Silver Slug" -Sold |
#9
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I was going to ask, "how do I tell?",
Here's a thread on it, I'll report back: Auxiliary Water Pump - Mercedes-Benz Forum. HOWEVER, the pump is to provide heat at idle speed, and I'm not getting significant heat at ANY speed. It's warm, but not retina blasting hot like it should be at max heat.
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1984 300CD |
#10
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You need to backflush the heater core like I said.
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'84 190D 2.2 5MT (Red/Palomino) Current car. Love it! '85 190D 2.2 Auto *Cali* (Blue/Blue) *sold* http://badges.fuelly.com/images/sig-us/302601.png http://i959.photobucket.com/albums/a...0/sideview.png |
#11
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Quote:
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2004 F150 4.6L -My Daily 2007 Volvo XC70 -Wife's Daily 1998 Ford F150 -Rear ended 1989 J-spec 420SEL -passed onto its new keeper 1982 BMW 733i -fixed and traded for the 420SEL 2003 Volvo V70 5 Speed -scrapped 1997 E290 Turbo Diesel Wagon -traded for above 1992 BMW 525i -traded in 1990 Silver 300TE -hated the M103 1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one 1979 Silver 300D "The Silver Slug" -Sold |
#12
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Feel your hoses, it can tell you a lot. Quick touch, let go, then slightly longer touch, let go, before it gets uncomfortable. You will not be able to measure temperature accurately by touch, but you can tell if one hose is hotter than another by how long you can your keep hand on them.
Feel the in/ out hose on the monovalve as well as the hoses into the firewall to/from the heater core. They should be similar in temperature. If not, monovalve may be blocked or heater core may be blocked. At full heat, monovalve/ heater core hoses should be less hot than the upper radiator hose (because it is further away from it), but not by a lot. If it is very cool in comparison, you may have some coolant flow issues. I find it very useful to start the engine cold and feel all coolant hoses as the engine warms up, which shows you the flow path.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#13
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After I reconnected the plug on my aux heater, I noticed a small increase in heat. Seems to come to temp a little faster. Not a huge amount, but measurable.
I'm due for a coolant flush; I think I'll back flush the core as well as do the MB flush as recommended, something about citric acid? EDIT To add, I found this link after posting this... http://dieselgiant.com/mercedes_citrus_flush.htm He mentions that his engine temp dropped about 10* after doing the flush, whereas mine normally runs a bit above 90*, not at 100* like others have mentioned. That makes it seem like mine doesn't have much corrosion in it... I'd be interested in thoughts on that, especially if the OP doesn't mine the sideline.
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--------------------------------------------------------------- 1998 VW Cabrio 2001 Audi SomeRoad A/T (no air suspension) 2003 Audi DeadRoad M/T (no vroom, for later) 2002 Audi NoRoad A/T (nothing under the hood, being rebuilt) |
#14
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I had this problem this fall on a 1983 300TD and checked the usual suspects--turned out to be a loose connector on the box of electronics that lives behind the glove box, not sure if that is the CCU you refer to or not,--the connector fell out in my hand as soon as I touched it. Easy to check if you haven't.
Peter |
#15
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Are you saying flush the whole system with a hose, or just blast the heat with the front of the car raised above the rear?
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1984 300CD |
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