My lukewarm heat turns cold after 8 minutes

"Niquemarshall" (dominiquemarshall)
11/15/2014 at 15:36 • Filed to: None

Heater has never worked in this car, only blows lukewarm, and after about 8 minutes it begins to blow cold. Thermostat was changed last april which helped a litle, coolant is properly filled, water pump has just been changed, coolant been flushed, auxiliary pump replaced.

I did notice the heater valve had the vacuum line disconnected so i reconnected it, no result. Also the heat got a bit warmer after the aux pump change, but still feels lukewarm and blows cold after a while.

1992 Mercedes Benz 190 2.3L

DISCUSSION (10)

fishtankwog > Niquemarshall
11/15/2014 at 15:56

What sort of vehicle? Symptoms are that of an airlock - an air bubble at the high point of the system...

Niquemarshall > fishtankwog
11/15/2014 at 16:01

Its a MB 190e 2.3L

Racescort666 > Niquemarshall
11/15/2014 at 16:12

My vote is bad heater core.

Niquemarshall > Racescort666
11/15/2014 at 16:13

bad vs a clog? that would suck to take 22 hours to replace that thing.

Racescort666 > Niquemarshall
11/15/2014 at 16:23

Could be clogged too. Most people I know that have had problems with heaters have replaced the heater core although it's been on vehicles where they were fairly easy to replace (Chevy Blazer, Pickup trucks, etc).

If it's clogged, I wonder if there's a good way of flushing it. Maybe disconnect the lines and hook up an air line to try and force out the gunk from the other direction?

Arben72 > Niquemarshall
11/15/2014 at 16:37

Sounds like you might need to bleed the system.

Niquemarshall > Arben72
11/15/2014 at 16:56

its already been bled. no longer needs topped off.. also MBs have self bleeding systems

gogmorgo - rowing gears in a Grand Cherokee > Niquemarshall
11/15/2014 at 17:10

Poor or no heat would indicate poor or no flow through the heater core. If the heater valve was only partially open for a while, or the pump pushing coolant through it was failing (I'm assuming that's what the auxiliary pump would do, I've never encountered one before), the low flow would lead to an accumulation of crap in the heater core (especially if tap water was used in the cooling system or it hadn't been changed for a while) and this would eventually block the core. This is particularly common in warmer climates where the heater doesn't get much use and it doesn't matter so much if you top up with tap water. (Tap water's common here too, but it absolutely needs antifreeze in it, which usually contains enough stuff to prevent accumulation of crap... but not always) Flushing from the radiator wouldn't do much to fix this, since no flow through the heater means it wouldn't get flushed. A new pump could have increased flow, causing improvement, but once the heater core starts clogging, it only gets worse.
I would recommend trying to flush the heater core directly. If you can, pop off the lines to the heater and try running water through the heater in both directions. If it's above freezing where you live, you may find a garden hose helpful, although the full power of household pressure could burst something in your heater if it's obstructed, so connecting the two should only be done wisely.
If your heater is the highest point of your system and you do have an airlock, filling your system from this point could be helpful in eliminating it. Alternatively, try to find out the procedure for "burping" your cooling system.

Of course you could also have a blend door issue. Most vehicles have a blend door that combines fresh air from outside with air through the heater. This door could stick in either position, and if it's stuck in the fresh position, you've got no heat. Older vehicles with slider controls for heat will typically have a cable driving this door, and it's common for it to fall off at either end. It could also be vacuum or electrically driven.

The above are suggestions based on my limited experience with vehicle HVAC. I have no idea how your system works or what might be an issue.

I just had a catastrophic failure of the heating system in my Lada. The heater flow valve failed, initially just spraying a mist of antifreeze into the air, but then it developed from a spray into a gush and puked most of my coolant into the passenger footwell. I've fixed it (bypassing the valve for permanent heat), but am not certain how to go about getting the antifreeze out of everything. Good luck in finding your solution!

Niquemarshall > gogmorgo - rowing gears in a Grand Cherokee
11/15/2014 at 17:47

i will check into that. I did run tapwater thru the car during the last month because it was leaking

AMGtech - now with more recalls! > Niquemarshall
11/15/2014 at 18:59

Probably a plugged heater core.