2004 W211 E320CDI OM648 Getting Hot

[Nilrem]

Hi Gents, I'm a long time lurker and tinkerer of cars looking for help before I start pulling my hair out please!

My car is a 2004 W211 E320CDI OM648 engine.

Symptom is that the cars temperature will start to climb above 90 degrees at motorway speeds or under heavy load say like climbing a hill on a motorway.

As soon as I see the temp climb I put the heater blower on high and on hot and the temp starts to drop.

Obviously by putting the heater on I am increasing the coolant circuit and the car can then cope with the demand placed on it.

The confusing part is that the car is quite happy to be driven around town all day or even sat in traffic and the temp stays at a steady 90.

My thinking is that the demand on the cooling system is at it's highest when in town or in traffic so I can't understand why she gets hot at high speed with all the air passing through the radiator.

I have checked the fan which appears to be operating correctly at both speed stages.

I am not losing any coolant and the oil has just been changed and no sign of mayo.

I have had STAR Diags done which showed nothing and replaced the following parts with either genuine or OEM;

Expansion Tank Cap
Thermostat
Coolant
Top and Bottom Radiator hoses
Waterpump
V (Aux) Belt

I'm thinking radiator next but surely that would affect town driving as well?...confused

Any idea's appreciated please as I've run out.

Thanks for reading
Pete

 

[markjay]

Welcome Nilrem.

I am assuming yout 2004 car does not have a DPF?

 

[Nilrem]

markjay, You're right no DPF

 

[skippyjasper]

Correct coolant and mixture?

 

[skippyjasper]

Radiator airflow blocked by debris?

 

[clk320x]

Radiator airflow blocked by debris?

How would it be ok in town then though?

 

[Nilrem]

@skippyjasper 50/50 mix of MB325.0
@clk320x my thoughts exactly...this one has me stumped at the mo

 

[skippyjasper]

How would it be ok in town then though?

Perhaps using 'blocked' wasn't the correct word.

What I'm thinking is that some of the radiator surface area may be compromised by stuff. I had this experience with another vehicle. Was OK at low speeds including around town. Got hot on the road.
Ordered new radiator as I had replaced similar items to the OP. When I took the old radiator out it was virtually plugged with flotsam.
Could have washed it out. Used the new one as there was a crack in one of the hose mountings.

 

[Nilrem]

My next step is to try a rad flush type product, after that radiator out and pressure flushed or replaced

 

[brucemillar]

Okay
I had "similar" on my Pajero. Fear not it is still a sealed cooling system. It was the radiator that was blocked. I bought an infrared thermometer from Screwfix for about £35 quid. The one has the laser point & shoot red dot on it. This allowed to see "exactly" what the temps in the cooling system, by pointing the laser where I wanted to measure. Ran the car up to temp and worked my way across & down the radiator. This showed two large cold spots in the radiator. Had it re-cored and the problem was solved £90. A new rad was NLA;^(

Debris between the AC and Engine coolant radiators or and ATF coolers is fairly common and will also (as has been mentioned) lead to poor cooling flow over the system. A weak or failing Electric fan will also cause these issues and can be difficult to spot if the fan continues to spin as you would expect it. By spinning it may not be pushing enough air.

Does it get worse if you leave the AC ON or Off?

The first thing to check is for a leaking (micro leak) header/radiator cap. These can leak and allow coolant to lose pressure unnoticed by coolant loss in the initial stages. It can be smart, low cost replacement item. Or get or buy a pressure system test kit.

It does look like there is a lot to fail. But it is really either air flow, coolant loss, or pressure loss.

Coolant loss is easiest to spot - hopefully.

Good luck.

 

[grober]

Almost certainly radiator related- pressure loss or choked internally or externally as been said. It may or may not be related to the VALEO radiator issue where there is leakage between the autotransmission cooling loop which is internal to the radiator and the primary engine coolant circuit. This affected cars built from 2000-2003 ish. However there are usually drive train symptoms if this is the case.
see
Valeo Radiators and Gearbox damage - Page 1 - Mercedes - PistonHeads
which has links to the` subject on here. There is a chemical test for glycol in the transmission fluid which can be done.
Cure in either case is a new radiator---- NISSENS are a reputable replacement make. You may wish to consider a separate transmission oil cooler at the same time if the car doesn't have one already?

 

[Nilrem]

Thanks for all the replies chaps
@brucemillar I've replaced the expansion tank cap and have fluorescent dye in the coolant so it's easier to spot if there's a leak and none spotted so far
@grober I had the Auto box serviced recently by my local independent MB specialist and there's no sign of the dreaded water in the ATF

I think as you both suggest either the radiator is partially blocked or there is debris in between the A/C rad and the engine rad restricting air flow, so that's where I'll go looking next.

Thanks again!!

 

[brucemillar]

I am trying to remember what I went through with my woes. But a few things to keep in mind:

1) Most "modern" cars use a comedy temperature gauge. Marked blue at one end and red at the other? These give a very poor indication of what is actually happening in a sealed system. Other than they rely heavily on the user spotting the needle moved out of the middle (normal) operating range. To get a real idea of true temps you need an infrared thermometer or a calibrated gauge . That can be important, as a faulty/poorly calibrated gauge can see you fixing a fault that does not exist!!

2) A sealed system will fluctuate a fair bit in it's boiling point (IIRC up to 25/30 degrees C) This is dependent on coolant type, quality and strength as well as having a truly sealed system.

Other an that it is looking for the

Fans
Thermostat
Radiator(s)
Water Pump

To cool and push the coolant through the system. Air Con, puts a big load onto any cooling system in hot weather, remembering that the system may well already be operating at a higher than normal temp due to ambient engine bay temps. It is worth taking a look at the temps with the AC off and On. Just to see if the AC is effecting the load. Pi hole leaks can be a killer as the coolant escapes as high pressure boiled steam that you may only spot as a drop in level or as you have correctly have done, using a dye in the coolant.

Good Luck..

Bruce

 

[Smiley]

I had exactly the same symptoms on a 124 diesel estate - and as has been suggested here - it was indeed the radiator. To check it get the engine up to temperature then run the palm of your hand across the front face of the rad - you will find cooler areas - this is where the rad is not flowing as well as it should be. A new rad is the way to go - Behr or Nissins.