Oil in engine coolant

[John A Waddelow]

Good morning.
Driving my 1999 MB E240 Elegance Estate with just over 160k on clock from S to N London on North Circular yesterday and got stuck in very heavy traffic (27m took over 2h).

Radiator fan warning light came on and temp started to rise, so put heater on full blast which kept temp down until arrived at destination.

Let engine cool down and checked water level, only to find oil in coolant but no significant drop in coolant level.
Checked oil level which was low but no obvious signs of coolant in it and no signs of cloudy water vapour from exhaust.

I risked driving home after as would have been logistical nightmare leaving it there.
No obvious problems en route except for Radiator fan warning light coming on again once engine reached temp but didn’t overheat unduly and ran smoothly otherwise.

I suspect this is more likely to be oil cooler leak rather than head gasket/engine block problem, but your thoughts and advice would be much appreciated.

Assume this and radiator fan are totally separate problems.

Also, as the oil level didn't run dry what other damage could I have done?
John W

 

[RhodieBill]

Sorry to hear of your issues. But personally I would be looking into the Radiator Fan issue primarily.......

 

[John A Waddelow]

Sorry to hear of your issues. But personally I would be looking into the Radiator Fan issue primarily.......

Thanks RhodieBill (Salisbury/Harare?).

I’m addressing the Radiator fan problem first, while deciding on coolant problem actions, as I think this likely to be either thermostat/temp sensor switch or possibly fan motor, although I always seem to attract the fickle finger of fate when I think things relatively easy and straight forward!

 

[mioba]

Whip your oil cooler off. Seal the ends with pipe. Chuck it in a bowl and blow the pipe. A leak will be aparent.

 

[Mr Greedy]

The first thing I would be checking for the cause is thermostat operation and engine operating/coolant/oil temps.
A boiling engine can cause oil/water mixing whereas under correct operation it would never happen.

Are you able to monitor these live whilst driving, potentially with a glamourous assistant? Using a data connection? Not sure if 1999 has OBD.

You need to understand if the fan's kicking in because there's something wrong with the fan, or it's kicking in doing it's job because it's hot, which means something else is wrong.

It's not that hot yesterday and especially today, and during driving (excluding massive, high speed steep hills) I would expect the thermostat to keep the temps rock solid once everything is up to temperature.

If it's not keeping it steady and the fan is operating correctly, I'd start looking in the following order at:
Thermostat.
Blocked radiator, either internally with crud or externally with sand, dust and mud.
Water pump.

There's been a rash of late 90s Mercs on the forums recently with over heating due to blocked radiators. This is often indicative when helped by blasting hot air into the cabin, because the small in dash radiator isn't blocked. New rad would be the cure if this is the case, and is a DIY and not the most expensive job in the world. Plus, if the rad is old, it's a good time for a coolant flush and refresh.

Good luck and keep us updated.

 

[John A Waddelow]

Thanks for that interesting and constructive input Mr G.
I feel sure that the overheating is caused by lack of fan operation.
Until yesterday once heated up my temp gauge has read very stable around the 80 degrees C level with very little movement under all ambient temp and driving conditions.
Then yesterday I suddenly got a diagnostic dashboard message/crude pic indicating a radiator and fan not working, and my water temp started climbing in the very heavy traffic conditions.
I’ve had no problems with this before so suspect either temp sensor or fan failure rather than radiator blockage but we’ll see.
Unfortunately I can’t find a diagnostic UBD port so it’s difficult to monitor what’s happening while driving, but think I’ll drive her tomorrow until she starts overheating, then stop and check if fans running.
I’ll also see if I can jury rig a cable from the fan motor to my digital multimeter which I can then place inside the cabin to check whether it’s getting a switched voltage as temp increases.
On that subject, after I realised there was something wrong yesterday the temp had crept up above the 120ish level and was bordering on the red. I suspect that the pressurised cooling system has a boiling point of around 130 so wouldn’t be surprised if that was reached. That was when I thought to switch on the internal heater matrix to see if temp dropped, which it did relatively quickly.
I hadn’t considered high temp causing water/oil mixing but when I first checked yesterday it almost looked like it had emulsified a little, so maybe that’s what happened.
I’ll focus on the fan side initially and once that’s resolved see how that leaves things.
Always reluctant to start removing eqpt with plastic fittings as these usually denigrate with age and break but situations dictate necessity.
I’ll update as situation progresses over next few days, although how I’ll find time is another problem.

 

[LostKiwi]

The first thing I would be checking for the cause is thermostat operation and engine operating/coolant/oil temps.
A boiling engine can cause oil/water mixing whereas under correct operation it would never happen.

Are you able to monitor these live whilst driving, potentially with a glamourous assistant? Using a data connection? Not sure if 1999 has OBD.

You need to understand if the fan's kicking in because there's something wrong with the fan, or it's kicking in doing it's job because it's hot, which means something else is wrong.

It's not that hot yesterday and especially today, and during driving (excluding massive, high speed steep hills) I would expect the thermostat to keep the temps rock solid once everything is up to temperature.

If it's not keeping it steady and the fan is operating correctly, I'd start looking in the following order at:
Thermostat.
Blocked radiator, either internally with crud or externally with sand, dust and mud.
Water pump.

There's been a rash of late 90s Mercs on the forums recently with over heating due to blocked radiators. This is often indicative when helped by blasting hot air into the cabin, because the small in dash radiator isn't blocked. New rad would be the cure if this is the case, and is a DIY and not the most expensive job in the world. Plus, if the rad is old, it's a good time for a coolant flush and refresh.

Good luck and keep us updated.

I'm curious to know how overheating (of the level described) can cause oil/water mixing?

The two systems are kept totally separate at all times.

A 1999 car does not have OBD2 - it uses the 38 pin round connection for diags so has a very limited set of tools available to read codes or look at live data (Star and Carsoft are about the only currently supported ones I'm aware of).

OP - as others I'd be inclined to fix the coolant fan issue first.
When you say there was oil in the coolant how much are we talking?

 

[John A Waddelow]

Thanks for that input LostKiwi, explains why I couldn’t find OBD2 connection socket.

Must also confess ignorance with regard to how/where/why water/oil could mix under boiling engine coolant conditions.

After I’d left the car long enough to cool down and depressurise the cooling system I removed the screw on coolant reservoir cap and there was obvious thicker oily fluid inside cap and around inside of reservoir neck and expansion overflow pipe, but couldn’t see to assess further.
I’ve had the car for just under 2 years and about 5000 miles during which time she has used a couple of pints of oil and I don’t remember having to top up coolant.
I have only been filling up every 6-8 weeks and haven’t checked oil or coolant for some time.
Yesterday oil level was almost at low dipstick mark when I topped her up, with coolant close to full.

 

[LostKiwi]

Thanks for that input LostKiwi, explains why I couldn’t find OBD2 connection socket.

Must also confess ignorance with regard to how/where/why water/oil could mix under boiling engine coolant conditions.

After I’d left the car long enough to cool down and depressurise the cooling system I removed the screw on coolant reservoir cap and there was obvious thicker oily fluid inside cap and around inside of reservoir neck and expansion overflow pipe, but couldn’t see to assess further.
I’ve had the car for just under 2 years and about 5000 miles during which time she has used a couple of pints of oil and I don’t remember having to top up coolant.
I have only been filling up every 6-8 weeks and haven’t checked oil or coolant for some time.
Yesterday oil level was almost at low dipstick mark when I topped her up, with coolant close to full.

The 240 engine can use a little oil (I'm on my third now) and it can be a partially blocked breather causing excess crankcase pressure to push oil past the rings.
My E240 (2001) with 166k is using about a litre every 3000 miles at present. I'm not concerned.
One of the 240s was using a litre every 500 miles at just 80k miles and that was down to a blocked breather.

Fix the fan issue then remove the oil cooler and test it as mentioned earlier. If it's not had a coolant flush lately do that too. Reassemble with fresh coolant (for testing you can use plain water) and see if the oil returns. Once happy with it drain some of the water and refill with the correct coolant.

 

[John A Waddelow]

Thank you Lost Kiwi, sounds like sage advice and will follow that.
I’ll have to fit in somehow over the next week or so but will post update when sorted.
No room in garage as I have a mothballed Camaro in there so will need to ensure dry weather and coincide it with working around current heavy football and business commitments.

 

[John A Waddelow]

Just one further thought.
Perhaps a silly question but after all the problems with multiple sensors on my old Jags though it better to ask than feel silly after.

Are there multiple coolant temp sensors feeding instrument panel and control circuits or just the one, and if multiple where is the fan control circuit one located?
Being a little lazy asking as I haven’t yet spent any time chasing this problem.

 

[Mr Greedy]

I'm curious to know how overheating (of the level described) can cause oil/water mixing?

My suggestion (and it is only a suggestion, so feel free to correct me if it is stupid) is that under 'normal' operation, any weaknesses in gaskets or oil/water heat exchangers is not put under any serious stress, and so would never show a weakness that might be underlying resulting in cross contamination of oil and water. But, if the engine overheats, the increase in pressure and heat load, differential thermal expansion of metals etc might reveal an underlying fault that would have never shown itself if the car wasn't operating in an overheated state.

Again, please feel free to correct me if this is stupid, as I'm not a professional mechanic and only have an amateur DIY enthusiast understanding so I don't have much real world garage experience of whether this is a possibility, or simply dream world territory on my part.

 

[John A Waddelow]

Apologies for delay, but after further checking eventually decided it was problem with oil cooler which I replaced and everything good.
No overheating or undue further loss of oil. Fan working again but not sure why as I couldn’t find anything wrong!