"The heat" meaning heat inside the cabin or the motor's operating
Motor supplies cabin heat so motor must operate at 80 degrees C. or
there will be inadequate heat - and it's bad for the motor and fuel economy.
So if motor is below 80 degrees C. have a shop replace the engine
thermostat - it won't fix itself.
OK, the motor runs at normal temperature so the flow to the heater must
be restricted at higher engine speeds. Perhaps a heater hose has a sharp
bend that kinks and that cuts off the flow to the heater core. The
heater hoses run from the firewall forward to the heater control valve
and then froward to the front of the motor.
Another thought: I don't know if the heater control valve is mechanical
or vacuum powered so this is speculation on my part. If it's vacuum
powered a small vacuum leak could affect it; as the throttle is opened
for speed the engine vacuum falls a bit vs. idle speed vacuum levels and
that difference may be the clue. Speculation.
There is a hose that returns from the heater. This hose has bends but
no visible kinks. It loops around the oil filter into the top of the
The heater valve is vacuum operated. It was replaced a couple of years
ago. I replaced the rubber hoses that go to and from it. I'll visually
inspect the heater valve for any leaks.
T.G. Lambach wrote:
As an experiment, try partially blocking the front of the radiator with
a cardboard piece and watch the motor's temperature to avoid overheating
it. Then drive on the freeway and see if the cabin is warmer. If so the
engine thermostat is confirmed as the problem.
I changed the thermostat last year with no improvement.
Could it be the heater core. I flushed it and it improved initially.
Is there a better way to flush it?
As far as the auxiliary water pump, should I disconnect it and see if
there is a difference. I do hear/feel vibration at the outlet of the
auxiliary water pump and hose going to the heater core.
T.G. Lambach wrote:
Why would you suspect that as most likely? AFAIK, the aux pump on
most models is there to provide faster movement of hot water at idle.
The usual symptom is lack of heat at idle/low speeds, good heat at
highway speed, isn't it? On 116, the pump is disabled once the cabin
air comes up to temp and I've seen lots of folks here with various
models report eliminating/bypassing aux pumps and noticing little
On 190E, aux pump acts both as a pump and heater valve. On other models,
they are mostly mechanical pump that is next to the main waterpump which is
essentially a full time pump.
At high speed, the water pump is at full force but the nature of water or
air... always travel the easiest route. Since heater hose is more
restrictive, less flow which means less heat.
Could it be the heater core. I flushed it and it improved. Is there a
better way to flush it? As far as the auxiliary water pump, should I
disconnect it and see if there is a difference. I do hear/feel
vibration at the outlet of the auxiliary water pump and hose going to
the heater core.
Take the pump off the car... and rig it up to a hose in bucket and see if it
pumps water out.
Reverse flushing the heater core is the best... rig up something so you can
hook up your garden hose to it... and other end free or into a hose to out
of engine area.
the easiest and cheapest is to exchange the thermostat rule that out,
first you know about the heater valve being vaccum operated so just
check the pipes, if you found a improvment when flushing the matrix
that might be your problem,mine is the same but its a twenty year old
190 so i just live with it try fushing the matrix both ways to remove
sediment best of luck
"T.G. Lambach" wrote
> "The heat" meaning heat inside the cabin or the motor's
> Motor supplies cabin heat so motor must operate at 80 degrees
> C. or
> there will be inadequate heat - and it's bad for the motor and
> fuel economy.
> So if motor is below 80 degrees C. have a shop replace the
> thermostat - it won't fix itself.
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