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My '97 E420 lost a fitting, spilled all it's coolant over the road, temp went straight up and after a tow is now in the hands of a mechanic. They fixed the fittings, bled and pressurized the system with new coolant, and started it up - it's still overheating. They replaced the thermostat - still overheating. They just removed and checked the water pump - all looked fine. If it continues to overheat, they are baffled and I'm faced with taking it to the friggin' dealer and paying ridiculous labor costs. I'd rather not do that, but they don't know what else could be causing it. I've never had any cooling issues at all with this car, can anyone provide some tips or something else to check?

Thanks!
 

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E320/E250 Bluetec Ford F350 6.7l
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What kind of professional mechanic can not troubleshoot the cooling system?
Get IR thermometer and trace the temperatures.
Quit taking your MB to butchers ;)
 

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1990 Mercedes-Benz 420 SEL(RIP),1997 Mercedes-Benz E420
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Fan Clutch. Are your fan blades damaged? This would cause noticeable heat.

Inspect the lines the mechanic fixed. Are they on tight. If low coolant was the only problem why are you having so much trouble I wonder. Were you in the presence of your mechanic during your repairs. Can you say with complete certainty that you "trust" your mechanic to do the work.
 

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2005 W215 CL500
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My '97 E420 lost a fitting, spilled all it's coolant over the road, temp went straight up and after a tow is now in the hands of a mechanic. They fixed the fittings, bled and pressurized the system with new coolant, and started it up - it's still overheating. They replaced the thermostat - still overheating. They just removed and checked the water pump - all looked fine. If it continues to overheat, they are baffled and I'm faced with taking it to the friggin' dealer and paying ridiculous labor costs. I'd rather not do that, but they don't know what else could be causing it. I've never had any cooling issues at all with this car, can anyone provide some tips or something else to check?

Thanks!
What do you mean lost a fitting? What fitting?
 

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Discussion Starter #5
I trust this mechanic to know what he's doing. The car had a slow coolant leak 4 weeks ago, I took it in and they replaced a hose connection within which a plastic fitting had broken. 2 weeks later, I was idling at light when I smelled coolant, as I pulled away from light I saw a large puddle of coolant on the road, my low coolant level warning came on and I then watched the temp gauge rise dramatically. I pulled over, saw coolant spray on the rear of the engine block, and got towed.

It was another broken plastic fitting, this time on the larger heater hose assembly. They replaced, refilled with coolant, and the engine was still overheating. They have replaced fan clutch, thermostat, checked the water pump and it's fine, drained & flushed radiator, and it is still overheating - it doesn't take much either after idling a trip around the block will cause it to overheat.

He thinks they may have an air pocket in the lines, but is bleeding the system normally.
 

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E320/E250 Bluetec Ford F350 6.7l
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If it overheats from cold start going around the block, that means you have no coolant circulation. Could be closed thermostat, broken pump impeller or strange blockade in the system.
Mechanics dropping parts into the car on customer valet don't have my respect, so I will not go farther.
 

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Current 2017 GLE350, 2007 S550, 2002 S430, 1998 ML320 Deceased 74 240D, 92 400E, 97 E420, 13 GLK350
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M119's trap air in the upper hose and plenum sometimes and vapor lock the water pump. There is a vent at the forward section of the engine to relieve this high point air trap. I am loathe to open this vent and use a different method.

I've changed the coolant in our E420 twice, and each time have used the easier method of squeezing the upper hose to 'pump' some water into the system and help eliminate the vapor lock. If your car has this problem, it will 'gurgle' for a bit when you squeeze the hose. You will also need to add a bit of demin water when the air bubble comes out.

In my expeience, the M112 and M113 don't seem to have this problem.
 

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1997 E420
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M119's trap air in the upper hose and plenum sometimes and vapor lock the water pump. There is a vent at the forward section of the engine to relieve this high point air trap. I am loathe to open this vent and use a different method.

I've changed the coolant in our E420 twice, and each time have used the easier method of squeezing the upper hose to 'pump' some water into the system and help eliminate the vapor lock. If your car has this problem, it will 'gurgle' for a bit when you squeeze the hose. You will also need to add a bit of demin water when the air bubble comes out.
So you would just open the coolant tank cap and squeeze on this hose? I just had my radiator changed and I don't think the mechanic did any air bleeding..
 

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MB engines don't require any special air bleeding from the cooling system, but they do require topping off system after the thermostat opens.
Since the thermostat is on the return hose and it holds the air, sometimes the engine needs to get up to 105C for thermostat to open.
 

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Current 2017 GLE350, 2007 S550, 2002 S430, 1998 ML320 Deceased 74 240D, 92 400E, 97 E420, 13 GLK350
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So you would just open the coolant tank cap and squeeze on this hose? I just had my radiator changed and I don't think the mechanic did any air bleeding..
Correct. If it is air bound, this is a quick and easy fix.

The M119 traps air in the coolant system more easily than other engine types.
 

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Current 2017 GLE350, 2007 S550, 2002 S430, 1998 ML320 Deceased 74 240D, 92 400E, 97 E420, 13 GLK350
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Guy I hate to say it, but if combustible gasses are entering the cooling system, it would overheat.
boot - was the car driven with the engine temperature in the redline? That can cause the heads to warp and exhaust gases enter the coolant through a track in the headgasket.
 

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2004 SL500 Sport, 1997 Mercedes E420 Sport
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Overheating E420

My '97 E420 lost a fitting, spilled all it's coolant over the road, temp went straight up and after a tow is now in the hands of a mechanic. They fixed the fittings, bled and pressurized the system with new coolant, and started it up - it's still overheating. They replaced the thermostat - still overheating. They just removed and checked the water pump - all looked fine. If it continues to overheat, they are baffled and I'm faced with taking it to the friggin' dealer and paying ridiculous labor costs. I'd rather not do that, but they don't know what else could be causing it. I've never had any cooling issues at all with this car, can anyone provide some tips or something else to check?

Thanks!
This is probably too late for the OP but here is my experience. Immediately question the radiator. The plastic tanks can crack and leak both from age and towing damage. If you mix in the wrong antifreeze that can clog up the core too. Good quality Radiators are cheap and only take an hour or so to change out with the thermostat. This sounds like you are getting taken for a ride - Thermostat - 2 hours, Water pump 5 hours. Labor adds up fast!
 
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