Overheating - Stumped

[dylantaylor544]

Being summer here in England, the old Merc is grumpy. For some reason even though I have addressed all the regular overheating issues, I can not get it to sit at the usual 85. It usually goes up to the 90 line mark then above and sits there and after a while, maybe 20 minutes of driving then eventually slightly higher to which by then I usually stop driving it. It will not cool city driving once its got there and neither on the highway even at 70mph when it should have more than enough air. If you coast and have no petrol at hight speed all the way to low speed, only then will it drop down to 85 and stick there. Once it reaches that you can drive around a bit until eventually it starts to rise and you have to repeat the process.
It's had a new radiator
A new thermostat
A new water pump
That was my mechanic, so I assume new coolant(perhaps not)

No oil in the coolant reservoir
No losing coolant( I might add half a cup every 6 months)
So the question is if this is the head gasket? I wouldn't have thought so if no oil mixture or loss of coolant.

The next step would be to drain everything, flush, and install new good quality coolant with the proper mix, does anyone think contaminated water/coolant could be the issue?

Could the block coolant passages be blocked somewhere?

The car also has the Diavia aftermarket aircon , so its got the big condenser and two SPAL fans ,which was probably not designed for the car, can that block the air flow too much maybe?

With it sometimes being fine but in warm weather suddenly start increasing, could it be like an airlock that forms stopping circulation? (Random assumption))

I don't know how to make the AUX fans to come on earlier to help, I have heard them come on when it gets really hot, maybe doing this could help or is needed?

So other than that, completely stumped at what it could be. So just asking if doing the coolant is worthwhile and the possible cause or no, time to look at head gasket?

Any views would be helpful.

 

[AMGeed]

I believe the new thermostats open at 92c.
That could be why your car sits at 90c and isn't actually overheating at all.

 

[Sweetooth]

I once had coolant change at asked a dealership ,it started overheating,I took it back ,they unscrewed the expansion tank cap ,there was a rush of escaping steam.The car then ran at its normal temp

 

[Stocious]

Try a new rad cap/expansion bottle cap as there cheap and you can rule out that

 

[markjay]

Try a new rad cap/expansion bottle cap as there cheap and you can rule out that

~£35 from MB, or ~£9 from Febi.

 

[markjay]

On my W204 with the M274 engine, the coolant temperature (as viewed from the Mercedes me Adapter app, via the OBDII port) is between 95 and 105 degrees in city traffic. That's with the new thermostat.

 

[MrGreedy]

20 years ago a mate of mine had the same car. He was going to get rid of it so never got the problem fixed, but it developed the same problem.
He used to have to drive round with the windows down and the interior heater and fan turned up to the max. It didn't have air con.
That got enough heat out of the engine to keep temperatures under control. I only mention it as you could test if yours does the same thing, maybe this will help identify the possible fault?

 

[grober]

VISCOUS COUPLING ON THE FAN GONE? This is for a v8 but principles are the same

K6JRF Auto Page

 

[dylantaylor544]

20 years ago a mate of mine had the same car. He was going to get rid of it so never got the problem fixed, but it developed the same problem.
He used to have to drive round with the windows down and the interior heater and fan turned up to the max. It didn't have air con.
That got enough heat out of the engine to keep temperatures under control. I only mention it as you could test if yours does the same thing, maybe this will help identify the possible fault?

Thats exactly what I do when it gets to that stage, so summer drives are toasty . When i do that it stays at 85/87(which is my thermos opening temp, as rated).

 

[dylantaylor544]

VISCOUS COUPLING ON THE FAN GONE? This is for a v8 but principles are the same

K6JRF Auto Page

I had a new one of those too in case, which it does kick in when hot in traffic and brings it down quite quickly to 90, even 87, but not at the high speed of 70mph.

 

[dylantaylor544]

~£35 from MB, or ~£9 from Febi.

Also quite new, merc one no damage to springs or washer. I could try this.

 

[dylantaylor544]

So what is the correct temp in all yours opinion? In winter car sits happily at position 1., 87 degrees no problem, maybe up ever so slighty when under load and drops and can drop to 80 when coasting. THis im used to i used to own a 260e and thats how it operated, never often went to position 2 unless the weather was 38 , 40 degrees blazing sun(In South Africa at the time).
In summer is the issue as explained with this 280. It goes up to 87 and stays there for some time and then starts to rise and goes to position 2. Then I can feel the car is hot and engine labours a bit which is what I don't like. If I just drive it when its at potiion 2 and dont run my heaters with the windows down or go very easy on the gas, it can start rising higher.

 

[slade1]

Did the aftermarket aircon installer fit a larger engine radiator? How accurate is the gauge?

 

[MrGreedy]

Did the aftermarket aircon installer fit a larger engine radiator? How accurate is the gauge?

I don't know how much this would be the cause if it's overheating at 70mph, however, I think it's still worth investigating/eliminating.
I would have thought even on a 40 degree day, there would be enough air passing the rads to keep the engine cool.
An easy test will be driving it without the air con running, particularly at motorway speeds. If it's the same problem, it's not air con related. If it cures it, there's the answer.

 

[dylantaylor544]

I don't know how much this would be the cause if it's overheating at 70mph, however, I think it's still worth investigating/eliminating.
I would have thought even on a 40 degree day, there would be enough air passing the rads to keep the engine cool.
An easy test will be driving it without the air con running, particularly at motorway speeds. If it's the same problem, it's not air con related. If it cures it, there's the answer.

So no this is a standard radiator and all of the issues mentioned are with the aircon off. If I run the aircon it shoots up even quicker, I basically can't use it.

 

[grober]

I had a new one of those too in case, which it does kick in when hot in traffic and brings it down quite quickly to 90, even 87, but not at the high speed of 70mph.

WHEN i had a similar problem with a FORD it was down to restricted radiator capacity
[ partially choked] high speed cruising means more engine heat generation with cooling normally achieved thro radiator RAM AIR EFFECT- forget fans which serve low speed cooling. Either the radiator* is partially choked or the wrong size = marginal for heavy load situations as suggested - coolant system flush and change in radiator cured the problem

*radiator is the common factor- you can look for rad cool spots with a infra-red heat detector/ thermometer

 

[optimusprime]

Could some one say what engine we are talking about ... Yes i would change the expansion tank cap its 1.4 bar for all the petrol cars . Could be as temperature rises its getting past the cap and out in to the overflow bottle in the inner front wing .

 

[ivan1983]

Also you can remove the thermostat, place it in a pan with water and heat it measuring the temperature to see if it opens and closes as it should.

I do this when installing a new stat just to make sure it's working properly.

You could also try running it without a stat for testing purposes

 

[slade1]

Agree with grober, radiator flush, may have to do it a few times. The gunk is available at any car part shop. Are the hoses in good shape?

 

[dylantaylor544]

Could some one say what engine we are talking about ... Yes i would change the expansion tank cap its 1.4 bar for all the petrol cars . Could be as temperature rises its getting past the cap and out in to the overflow bottle in the inner front wing .
[/QUOTE]
Its an M104.942 with a 722.5 tranny and aftermarket Diavia Aircon(which is not in use when these problems occur)