Temperature raising while driving fast - SOLVED

[RobertK]

Admin edit: See post #36 for solution details.

I have a question about the following:
After replacing my thermostat (the old one was a bit of lazy) the temperature is raising when I drive faster:
For example:
180 km/ph it raises to 100 Degrees
190 km/ph it raises to 105-110 Degrees
200 km/ph it raises to 115 Degrees

When I drive in the city or at normal speeds it shows just under 90 Degrees and stay there independant which temperature the weather is.

Do you know what reason this could have ?
Blocking radiator ? Or second phase of the two extra fans are not working ?

 

[gsxr]

If the temps were normal before the t-stat replacement... you may have gotten a defective thermostat. I'd consider replacing it again. If temps were high with the old t-stat, something else is wrong.

Electric fans are not the issue, btw. The engine should remain under 107°C and never trigger the fans on high speed except in extreme conditions.

 

[RobertK]

With the old t-stat it was not that behaviour what I described. Besides the fact that it was a lazy one: warm up period was very long, the temperature gauge stays on all conditions under 90 degrees.

I forgot something: we have also replaced that thick short hose to the waterpump for a new original one.
I noticed that this hose is in the middle thinner than the one which came off my car. For that reason the throughput of water could be smaller I think ?

 

[gsxr]

What you describe sure sounds like a defective new thermostat. I assume a new Wahler/Behr was installed, or Genuine MB?

The hose should not affect liquid flow and wouldn't change temperatures measurably.

 

[RobertK]

The T-stat was replaced by a new Genuine MB one.

 

[gsxr]

The T-stat was replaced by a new Genuine MB one.

IIRC, forum members have reported defective Genuine MB thermostats new out of the box. I'd still start with replacing that first.

BTW, I am assuming the cooling system is full, and there's no air pockets, it pressure-tests OK, and there is no coolant loss following the 110-115°C engine temps.

 

[RobertK]

BTW, I am assuming the cooling system is full, and there's no air pockets, it pressure-tests OK, and there is no coolant loss following the 110-115°C engine temps.

There are no issues what you mentioned.

I will replace the T-stat first for a new one.

 

[RobertK]

There are two numbers in the EPC for the T-stat:
A116 200 315
A119 200 015

Which one is the right one ?

Now I have the A116 200 315 in my car (after some investigation)

 

[gsxr]

Almost all E500E's use the early 116- part number.
Only the last few hundred E500's produced would use the 119- number.

The early & late units are completely different and not interchangeable:

 

[gerryvz]

I have had horrible luck with the Mahle/Behr (aftermarket) thermostats.

I have had better luck with the Wahler (aftermarket) thermostats.

Both companies are OEM manufacturers for MB thermostats, for various applications. Most recently I installed a Wahler unit in my E500, last summer, and it has worked very well since.

I had very similar temperatures on my M104 (G-wagen) a couple of years ago -- it would get very hot running at high speeds. It was a defective Mahle/Behr thermostat that was only a couple of years old. A new thermostat fixed the problem and now the engine never sees 100C temperatures even in the very hottest summer weather with the air conditioning running HIGH.

If you cannot hear the high-speed fan coming on when the temperature shown is 110C or higher (or the design temperature of 107C), when you are sitting in the car and idling, then you also have an issue with that fan. You would need to check the temperature sensor, fuses, and relay that control the high speed of the fan.

When the fan comes on, it should FORCE the temperature down to the 90-95C area within a couple of minutes. Then the cycle repeats.

 

[gsxr]

On a related note, the MB thermostat design requires the t-stat to be 100% fully open in order to cool properly. This is because when fully open, it forces all coolant flow through the radiator, so the water pump only pulls in coolant from the radiator exit. If the t-stat is not FULLY open, the water pump will ingest a mixture of coolant from the radiator as well as hot coolant from the engine block. This could cause a hot-running problem. The more typical failure is slow warmup and running below 80C, but the opposite failure as Gerry describes is also possible.

 

[gsxr]

OH, and btw, if the fans are roaring (both mechanical & electric) and temps aren't coming down, that also points to a possible t-stat issue. I'm basing a lot of keyboard diagnosis on the fact your car did not run hot until the new t-stat was installed.

If temps go to 105+ but drop rapidly when the electric fans engage at 107C, that implies an airflow issue.

 

[RobertK]

Ok thanks for your comments.
I have ordered a new genuine T-stat from the MB dealer.

I will also check the correct working of both electric fans, both phases.
Airco on => running low speed
Above 107 degrees => running high speed

 

[RobertK]

I have checked the extra fans with airco on: they do not turn around.
I should that investigate first.
Make it any difference that the airco was on but not on cold temparature (I have climate control) ? Should they always run on low speed with airco on independent which temperature you choose ?

 

[JC220]

@RobertK What car do you have? A 500E?

Have you ever replaced the viscous fab coupling? Does it make an audible roar under certain conditions?

Usually the viscous fan is the primary reason for w124s overheating. The AC fans should not be required to run in order to cool the engine. The radiator and viscous fan should be capable of controlling the engine temperature on their own IMO. People fitting cool harnesses or whatever they are called to make the AC fans run all the time is simply a band aid and not addressing the root of the problem. #Need white paper

I would ensure your viscous fan coupling is operating at full efficiency. If it isn't the cooling system will never be operating correctly. It is the key item.

 

[gsxr]

Robert, you have a Japan-spec early 500E, correct?

The electric fans run on low speed only when refrigerant pressure exceeds 16 bar. If ambient temp is not hot, the fans may not run. To test the switch you need to connect a refrigerant manifold gauge and see if high-side pressure is over 16 bar. To test the relay/fans/wiring, you short the 2 wires at the pigtail of the red pressure switch at the receiver/drier, the fans should turn on low speed. If they still don't work, and the 30A strip fuse is good, the likely fault is a broken wire at the resistor behind the driver headlight.

@JC220 is correct, the fans ARE NOT required to keep the engine cool. They are intended to help with AC performance at low RPM / low vehicle speeds. The "CoolHarness™" is indeed only a band-aid hiding a different problem.

I agree that the next logical test would be the fan clutch, along with verifying airflow is not blocked ahead of the clutch. The clutch face requires hot air to engage, if airflow is blocked or if there is a cold spot on the radiator in that position, even a good clutch will never engage.

That said, the fact that the engine runs 90C at all times in the city and ONLY gets to 110-115C at high speeds, may indicate a different issue.

 

[RobertK]

Yes indeed I have a Japan spec 500E from 1992.

But I forgot something: I have to change the T-stat first for a new one and then looking if this happen again (rising temp at high speed). I am now busy with that

I understand what you both said about the electric fans. The 30A strip is not broken and I see no broken wires at the resister area behind the headlamp.

 

[gsxr]

You MUST test the fan by shorting the leads from the red switch (with ignition on). If the fans turn on low speed, great.

If the fans do not run, then you need to find out why. The broken wire is almost impossible to see without removing parts.

 

[RobertK]

First I have replaced the T-stat for a brand new OEM one yesterday. The windgap in the T-stat was not installed on top.
Now it is. A short drive yesterday evening give hope. The temp gauge stays under 90 degrees. On high speed I will investigate later

 

[TerryA]

@RobertK, Take the 30 amp fuse out to check it. My fans weren’t working properly due to corrosion on the contact areas and just had to be cleaned up. After that the fans worked perfectly.

 

[RobertK]

Still strange. The 30 Amp fuse is in good condition, I also replaced the thermostat for a new one (OEM) and also finally the cap of the expansion tank for a new one. I still have the impression that it runs warmer at higher speed (>105 degrees). The 2 fans do not run but that was not directly related to driving at higher speeds, right? This may also have to do with a too low level of Airco liquid I understood. I'm thinking of a radiator that is no longer good or the fan clutch ? What do you think ?

 

[RobertK]

It gives me a little bit frustration:

After replacing my:
thermostat for a new OEM (the old one was a bit of lazy)
Radiator for a new OEM one (the old one was a copper not OEM one)
OEM Behr Fan clutch replaced by an aftermarket one (RFN)
Expansion filler cap replaced for a new OEM one
All coolant hoses

Auxilary fans are tested and works well in both fases.

The temperature still raising when I drive faster:
Like I earlier said:
180 km/ph it raises to 100 Degrees
190 km/ph it raises to 105-110 Degrees
200 km/ph it raises to 115 Degrees

 

[gsxr]

• Does the cooling system ever lose any coolant?
• Have you verified the new RFN fan clutch is engaging and the fan is roaring to at least 3500rpm when hot?
• How old is the water pump, and is it OE or aftermarket?
• Is there any pressure in the cooling system (squeeze upper radiator hose) when the engine is cold?
• Has the condenser been cleaned / blown out and verified it is not blocking airflow to the radiator?
• Has the cooling system been confirmed to hold 15+psi and also the new OEM cap tested as well?

Also wouldn't hurt to check fuel mixture issues that could be causing high temps with a good cooling system. Correct 5.0L LH module, adaptation within limits, MAF & O2 readings normal via live data, exhaust system not restricted, brakes not dragging, etc etc...

 

[RobertK]

• Does the cooling system ever lose any coolant?

No, not that I have noticed.

• Have you verified the new RFN fan clutch is engaging and the fan is roaring to at least 3500rpm when hot?

You mean that it should roaring faster until at least 3500rpm when hot ? I should check that.

• How old is the water pump, and is it OE or aftermarket?

Is the original OEM one. Car had done 113k Km.

• Is there any pressure in the cooling system (squeeze upper radiator hose) when the engine is cold?

I should check that.

• Has the condenser been cleaned / blown out and verified it is not blocking airflow to the radiator?

The condenser looks quite new but I have to check that.

• Has the cooling system been confirmed to hold 15+psi and also the new OEM cap tested as well?

The coolant system has been checked and being held under pressure by MB Classic Center after installing the new radiator and RFN fan.

Also wouldn't hurt to check fuel mixture issues that could be causing high temps with a good cooling system. Correct 5.0L LH module, adaptation within limits, MAF & O2 readings normal via live data, exhaust system not restricted, brakes not dragging, etc etc..

Brakes are not dragging. The other things you mention, I do not know how to check that. The engine runs normal.

 

[036]

Did you try an old school trick and put heater on max while driving fast?
I used Thermostat for South Africa, helped a bit. It opens earlier.

 

[RobertK]

Good idea I think, I will try this.

 

[036]

At 1:02 and 2:10 you can see what i had driving fast.

 

[RobertK]

Allright, the temperature climbs also a bit up until 100 degrees, but mine increases more than that with that speed.

 

[036]

And it was winter, only plus 6C..... I was constantly looking at temp gauge, more often as at speedo or even road

 

[RobertK]

Allright, In winter I do not know if it is the same behavior what I described. In summer it is for certain.

 

[RobertK]

I forgot something; my LH module has the number: 014 545 17 32 and is in my opinion the right one.

 

[RobertK]

I used Thermostat for South Africa, helped a bit. It opens earlier.

Is that the one which opens at 71 instead of 84 degrees ?
What is the OEM number ?

 

[036]

No idea anymore,very long time ago. Yes, it was South African one.

 

[gsxr]

Stock t-stat is fully open at 94°C. Opening sooner will not cure a problem where engine temps exceed the temperature where the t-stat is fully open.

 

[gsxr]

Also, you should focus on curing the new problem, and see if the temp problem still exists when power is back to normal:

Low performance during acceleration | Troubleshooting and Diagnostics

I have a new problem with my Japan import 1992 500E: The performance during acceleration between 3000-5000 rpm is very low, it looks like the car is standing still and stays on the same speed. The engine revs during this. It also not revs to 6000 RPM. I doubt if this is limb-mode because of the...

www.500eboard.co

 

[RobertK]

Good news !
Problem with the bad performance is solved. New cats installed and it runs much, much faster and better.
The old cats were totally internal destroyed. MOT also not passing because of too high CO yesterday with the old cats.

 

[RobertK]

I had never expected such a different in performance between that original defect, clogged, internal seperated cats and this one. It is like if I have another car. So much faster, also in lower RPM's.

I think that my heating problem at high speeds is also solved but I have to test that when I have the oppertunity to do that:

 

[RobertK]

I have noticed that the temperature needle stays on the same spot (84 degrees) during speeds above 200 km/per hour during several minutes or more. At all circumstances it stays on 84 degrees by the way. Problem is solved !!

When selling it to a Cats recycle firm we noticed that one of my old cats had lost half of its content.