W124 underbonnet temperature?

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BlueQuinn

Active Member
Joined
Jun 4, 2013
Messages
150
Location
London
Car
Mercedes-Benz 300TE-24
Driving from London to Richmond yesterday, about 12 miles, fairly free flowing traffic, when I parked up in Richmond the right hand side of the car seemed very hot, and the wing was very hot as well as the bonnet.

I know that side has the exhaust manifold on but is this normal? There's a lot of space there for air to circulate and cool the exhaust.

My bonnet is missing the big pad on the underside. Would that be the problem?
Water temp was normal on the gauge all the way.

I'm sure it's nothing, but I'm new to all this car driving business so just thought I'd ask the more experienced.
 
124's do have a right side engine mount cooling duct that should help in summer. Mechanics often just leave them off...
 
ENGINE COMPARTMENT PANELLING, GASOLINE VEHICLES CHASSIS SHEET METAL íà Mercedes 300 E-24, AMG 300 E 3.4 (124.031) | Êàòàëîã çàï÷àñòåé Mercedes, ïîäáîð àâòîçàï÷àñòåé äëÿ ëåãêîâûõ àâòîìîáèëåé Ìåðñåäåñ (ðåãèîí Åâðîïà) ïî àâòîêàòàëîãó.

and

ENGINE MOUNT COOLING CHASSIS SHEET METAL íà Mercedes 300 E-24, AMG 300 E 3.4 (124.031) | Êàòàëîã çàï÷àñòåé Mercedes, ïîäáîð àâòîçàï÷àñòåé äëÿ ëåãêîâûõ àâòîìîáèëåé Ìåðñåäåñ (ðåãèîí Åâðîïà) ïî àâòîêàòàëîãó.

Without the plastic underbody panel more air is liable to "bleed out " of the engine compartment rather than be forced back through it. [ Its a worthwhile replacement as it will help the aerodynamics and give you a few more mpg at high speeds]


edit:- think I misunderstood do you mean the large sound deadening lining under the bonnet-- that would certainly insulate the bonnet itself from engine heat transfer but not the wing.

I would also suggest checking the main engine cooling fan and viscous coupling is kicking in at the appropriate temperature and if the car has air -con that the 1or2 auxiliary electric fans in front of the radiator are working properly.
 
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That's the one grober!

This is on top of having the entire cooling system in good working order.
 
Thanks.
I did mean the insulating sound deadening pad. It's not there on my car, just a few rotten scraps of foam. It's on the list of things to get.

I'll check for the presence and efficacy of that cooling duct.

And indeed for the underbody panel and side panels. I'm sure they are there, but I'll double-check.

The car has aircon, which doesn't work, so would that prevent the electric fans kicking in?
Temp gauge is bang in the middle of the gauge, so I guess the cooling system is OK. Reservoir looks clean.
 
If the aircon doesn't work the electric fans might not kick in but should not be strictly necessary as there should be no additional thermal load. Try the "carrot test" on the viscous coupling on the main engine fan. If there is no sign of overheating then things are probably OK and you are just experiencing some HEAT SOAK in this exceptionally warm weather.
 
If your cooling gauge is bang on 80 in this sort of weather you are absolutely fine. Car engines have a huge amount of latent heat that will diffuse when the car is at a standstill, with no airflow, so some parts will actually be hotter than when they are on the move.
 
Well what do you know, the underneath engine cover panel isn't there either.

Another thing for the list...
 
Or the side panels, or the vent pipe.
hmmm. Now I'm trying to decide whether I care enough to bother replacing all that lot.

It seems fine without and I'm still getting 25mpg.
 
The underbonnet temperature on a W124 particularly the larger engine ones (320,280) is always high and is one of the reasons why the wiring loom degraded when Mercedes decided to fit wiring that was not up to spec.
In my experience the undertray makes very little difference to underbonnet temperatures.
 

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