Heat dissipates at highway speeds for 93 190E 2.3L

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Hello all, I have a 1993 190E 2.3L. The heat seems fine at the lower speeds, but at the highway speeds it seems highly inadequate. The ambient temperatures are in the mid 30s Fahrenheit. Does anyone have
any suggestions?
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CP wrote:

What does the engine temp gauge say? Is the engine temp normal or low? If low, I'd suspect it could be a bad thermostat.
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"The heat" meaning heat inside the cabin or the motor's operating temperature?
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.
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The engine temperature was at least 80C when this happened and at highway speeds of60mph and ambient temperature of 35 degrees Fahrenheit.
T.G. Lambach wrote:

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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.
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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 engine block.
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:

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Any other ideas out there?
CP wrote:

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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.
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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:

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It is most likely your electric auxilary heater pump has failed.
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Tiger 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 difference.
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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.
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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.
Tiger wrote:

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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.
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What about the heater core. Could it be beyond flushing based on the age of the car? Have you ever seen these heater cores replaced and the heat improves?
Tiger wrote:

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Yes... if someone filled the radiator with quick sealer... that definitely would cook the heater core... render it useless.
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..any easy way to fix that ??
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Not really... backflushing is the only way with turbulence as in on and off to shake loose anything that is in there. If it is really stuck, it is realllly stuck!
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I'd test the thermostat first. When was the last time the rad was flushed with citric acid?
The heat works well at idle?
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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 > operating > temperature? > > 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.
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