The heater core on my 1989 W124 300TE is leaking, at least I think it is since there is water on the floor in front of the front seats.
I was planning on bypassing the heater core until I get some time to fix it, then I see that the secondary water pump is leaking as well....I was told that the secondary was there for the heating system, if that is true and I need to bypass the heater core then I should be able to bypass that little electric secondary pump right and it should not adversely effect the system right?

Next question......If the system that the coolant runs through is shorter will the coolant temperature be higher?

Bypassing the pump shouldn't hurt anything, especially since you're bypassing the heater core altogether, and since since you're bypassing the heater core, engine temperatures should act the same as if you were running with the heater off.

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Streetside: 1987 Mercedes 300E Petrol Blue/Green
2014 Ford Mustang Grabber Blue
1999 Ford Ranger Green

Dockside: 1968 Eltro 17
1985 Silverton 34C

Thank you, I figured it would be ok but wanted to make sure....and it will be nice to have use of the car until I can get the parts shipped and the time to do the heater core repair.

Aux pump is there strictly to maintain flow in the core while at idle.
Euro cars may or may not have the aux pump, it's not std in the home country.

Many fail and owner's do not even realize that they are not functioning.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

If you do not block or restrict the flow, you're short circuiting the radiator.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Could this be another reason for owners seeing higher engine temps in some of these cars?

Also, if the coolant has a shorter path it is not cooling down as much as it should before it heads to the block to warm up again (more)....the longer system with the hoses and heater core would allow the coolant to cool down more and have a lower temp reading than the shortened system.

Or is it possible that I am over thinking the issue?

Standard on both my estates, UK models, but I doubt the home market is different. I repaired a failed one on the '93 and got a definite improvement in cooling, and reduced warm up time

ymmv

cheers!

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cheers!!

Had to bypass the heater on my 89 300e for a week due to a leaking matrix, ran fine with no difference in operating temp. It was a very involved job to change it though

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87 w124 zender 3.6 - 3.0 kompressor in progress!
96 w124 e300 diesel - slowly being modded
98 w208 230 kompressor - m103 testbed SOLD.
96 s124 om606 superturbo diesel 508bhp

Do you have the repair documented on here?

Afraid not, I did this job before becoming a member on this forum. It was a bit of headache to change, I had to remove the steering wheel, instument cluster, center heater vents, dashboard speakers, the a-pillar trims, lower dashboard panels, light control rotary switch, the wood trim covering the heater controls and hazard light switch areas. You can then unbolt the dashboard itself from the car.

Once you get that lot out of the way, you can now unclip the top section of the heater unit to reveal the core itself. Next undo the 3 alloy pipes running into the core, these are held in by 2 8mm bolts each (6 in total) and are jubile cliped at the other end. You can now pull the core upwards and finaly remove it from the car.

This was done on a uk right hand drive car, but I would think it would be the same as a lhd. By the time I had put it all back together and removed all the air from the system, it had taken an entire day to do the job.

__________________
87 w124 zender 3.6 - 3.0 kompressor in progress!
96 w124 e300 diesel - slowly being modded
98 w208 230 kompressor - m103 testbed SOLD.
96 s124 om606 superturbo diesel 508bhp

Ouch!!!! I knew it was involved but when you start breaking it down it sounds like even more of a pain.
Also, aren't there some modules that should be replaced while doing the job because if one go's bad you have to do the same amount of work as a core replacement?

Don't forget the evaporator core.
Replace all the vacuum door actuators.
Some actuators can be accessed without box removal, but not all.



Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

It is (was). Years ago, had a 86 300D non turbo grey mkt car without it.

Pump failure does not affect temp, coolant will push thru the pump.
Pump's purpose is only to promote circulation at idle, otherwise, it's not required. Disconnection or elimination of the pump does not make a noticeable difference. Very, very over-engineered.

Pumps main purpose as they age, is to blow the auto temp control box, requiring a higher current draw than when new.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Yes, and no.

Pump has no effect, but you're also bypassing the monovalve, which stops flow when the heater is off, so you introduce a short circuit for hot water.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

I got my secondary water pump (thanks Lee) but have another question.

Where the coolant line exits the head on the drivers side it t's off and a small hose runs along the firewall and up the passenger side where it connects to another pump and then it looks like it feeds through the windshield washer reservoir.
What is that extra pump and what is it doing?