Vito W447 temperature variation - rises at high throttle and diminishes with minimal throttle.

[dave783]

Greetings, everyone! I am experiencing a perplexing problem with my 2018 Mercedes Vito Minibus W447.

I have been experiencing random fluctuations in the temperature gauge. This weekend, I undertook an extensive 15-hour drive, and here are my observations.


Temperature decline: When travelling at a constant pace of 70 mph or maintaining a consistent RPM, the temperature gauge will remain at the standard 90 degrees. However, when I attempt to activate the heater, it emits frigid air. Upon momentarily releasing the throttle or shifting into neutral on downhill gradients, the heater resumes heating, while the temperature gauge descends to just over 40 degrees and fluctuates between 40 and 80 degrees for approximately one minute. There will be a little fluctuation before stabilising around 80 degrees and ultimately reaching 90 degrees when I resume normal driving. The heater will remain warm for around 15 minutes, sufficient to provide warmth once more.

The temperature rises: When travelling at a steady motorway pace (50-70 mph), the temperature gauge remains normal at 90 degrees; however, upon applying additional power, such as during overtaking or ascending a hill, the gauge exceeds 90 degrees. I would hear the fan activate. The amount of power applied, the incline of the slope, and the duration of power application will influence whether the temperature reaches 120 degrees or above. However, it will descend rapidly when I reduce the throttle.

When the temperature exceeded 120 degrees on the freeway, I had a complete loss of throttle response; regardless of my actions with the throttle, the van did not respond and began to decelerate. I had to stop on the hard shoulder for a few seconds, and it was only after the temperature approached 90 degrees that I regained throttle control.

I have replaced one thermostat, but it did not yield any improvement.

I possess a Xentry device, and no fault codes are displayed. I lack mechanical expertise, hence I am unaware of what to observe. Any assistance would be greatly appreciated.

[CyberNinja]

A comparable incident occurred with my Ranger truck when the coolant level became too low owing to a loose hose clamp. I tightened the clamp and replenished the coolant, but the temperature fluctuated significantly. It was ultimately determined that a substantial airlock was present. Following adequate bleeding, regular service was restored.

[dave783]

I considered the possibility of an airlock; however, the coolant level has consistently remained adequate, and there have been no recent alterations that would precipitate an airlock, unless it is feasible for one to occur spontaneously.

Nonetheless, I will conduct a comprehensive coolant flush to eliminate any airlock; I am uncertain about the complexity of the procedure, so it is prudent to entrust it to professionals. I will thereafter provide a report here.

[ByteStorm]

Is this the Renault engine from 2018?

[dave783]

It is the 2.1 Merc engine. Automated.

[TDudette]

A flush will substitute fluid for air.
Eliminating the final reservoir of air can be somewhat challenging on certain cars. It is necessary to identify the system's highest point from where it can be bled and to confirm that it is indeed the highest point in the system. The final point may occasionally necessitate elevating the corner of the vehicle where the bleed point is situated. Uneven terrain can determine the success or failure of the undertaking.

[PixelMaster]

An air bubble can certainly precipitate this problem. Air is a less effective conductor of heat compared to the coolant fluid. Upon the arrival of the air bubble at the sensor, the temperature gauge will indicate a decrease.

[dave783]

I have resolved the issue.

Despite purging both heater matrices of the Vito and refilling the coolant using a vacuum pump system for £120, the issue persists.


I changed the water pump, which appeared to resolve the issue.

I appreciate everyone's assistance.

[CodeCrusader]

I monitored the discussion until its conclusion to ascertain whether anyone proposed the water pump. Several years ago, my son's Galaxy exhibited same symptoms, prompting a local garage to attempt several solutions, similar to your approach, until I proposed that the water pump might have experienced a failure of the vanes from its plastic impeller. They initially dismissed my assertions, yet subsequently acknowledged my accuracy.

[dave783]

I initially proposed that to one of the mechanics working on the vehicle; however, he insisted on cleaning the heater core first, as he prefers not to replace components unnecessarily. Well, it is completed now.