W124 E220 running hotter than expected

[Lxb3]

Evening all. I wonder if someone can shed some light on a quandary...
The E220 seems to be getting hotter than I would expect, particularly on a long run. There's some evidence of mayonnaise in the coolant header tank, BUT it's old and the previous owner had the HG done - there's no sign of any new mayo forming after I cleaned everything within reach. The engine runs beautifully, uses no water or oil, no smoke, plugs not fouling; brand new thermostat from the main dealers (it was surprisingly reasonable), and sufficient coolant... the viscous coupling was knackered, so I replaced that with a new one, although the car doesn't tend to overheat in traffic - it just gets hot on a run.
One odd observation - the temp. gauge "spikes", it'll hover around the 100-mark but then suddenly jump up higher, and climb down again fairly quickly back to somewhere between 80 and 100.
So:

i) Is there any easy way to see if the water pump is doing its job properly? I'm guessing that taking it off would wreck the gasket.

ii) Any suggestions as to what else could be causing this kind of behaviour?

iii) Does anyone know of any treatment to remove any traces of mayo from the cooling system? Wondered if there might be build-up in the rad... and I'm not sure back-flushing would move it!

Free cup of tea and eternal gratitude to anyone with an answer.

 

[WDB124066]

I think there was an MB product for flushing oil from the cooling system. Not too sure about the other way round though other than an engine flush? Test it first on a small piece of sludge, if it dissolves you're in. I think MB do an engine flush.

 

[kth286]

You could have an airlock in the system - bleed it out.

 

[Vlad]

Or your existing radiator could be silted up....I've had to change a couple of radiators over the years on W124's due to this. Mainly caused by previous owners not changing or not adding coolant to the cooling system when its needed topping up (ie they've just added water).

Could also be your water pump thats on its way out.

 

[grober]

IRRC the coolant cleaner was citric acid based. Silted radiator sounds a good candidate other possibility is a dodgy temp gauge/sender unit or poor connection to same. Until you get a rock solid temp gauge reading pointless doing anything else.

ps airlocks in the system might give you irratic readings too.

 

[Lxb3]

I didn't see any bleed points on the system when I changed the thermostat... and it is a genuine MB one I've put on there. Plus I'd have thought that any air pockets would have worked their way out by now, it's done a fair few miles since the new coolant. Thanks for the suggestions though! I really must check the rad for "cool spots" after a run.

 

[Lxb3]

...does anyone know how to check the water pump's function?

 

[WDB124066]

Generally AFAIK if it isn't rising out on the open road but does rise in town then it is a water pump, or VC.

 

[Lxb3]

That's roughly what I've have thought - but it does the opposite, seems to be ok around town (lower revs, I presume), but on a run after about twenty or thirty mins the temp rises higher than what I would consider normal - which is what's leading me to think it's the rad silted up. Viscous coupling is new and appears to be working perfectly.

 

[WDB124066]

So, new rad or are you going to try a flush, then a new rad...??

 

[kth286]

Start engine from cold next time and leave the expansion cap/rad cap
off until engine gets hot - then fit cap on.

Might bleed air out.

The stat should always be fitted with bleed hole in the uppermost position.

 

[Lxb3]

I'll try a flush - nothing to lose, after all, except some coolant and a little time.

KTH - the stat on this was a sort of sealed unit, came built into its own housing with no bleed nut/hole on top. Thanks though!

 

[sub_zero]

Hi Lxb3. .
This may be late...I have the same issue with my car ,it is E220 1995 , in summer temp. Gauge always around 100C.
Clutch is new and no coolant leaks.
The rad. Is 21 years old now.could the rad. Be the guilty guy here?
By the way..never done coolant flush before.
Thanks