OM605 Overheats under load - Head gasket ? (I hope not)

[tsharkey]

I fixed the Diesel Delivery valves on my partners car. The o-ring on one was shot and it was weeping and was at times, hard to start.

Took it out for a test run and rev'ed it up to 4K through the gears (no where near redline). On way home, noticed the temp above the very standard 83°C. The gauge was flickering and it ramped right up to 120° before I shut it down.

Oh-no - I've done a head gasket I think .... But

1. It sits happily on 85°C if it's left to idle (only seems to climb if its under load)
2. With overflow / burp bottle cap off there is no bubbling / oil residue
3. No water in the oil

So is it a head gasket ?

Unlikely to be thermostat as I replaced with a new one about 12 months ago.

Also, the viscous clutch fan does not appear to lock (but both thermo fans are running). There is a quiet whine (like a dry bearing) in line with engine rev coming from the front. Could a dead fan or water pump cause it to overheat above idle even it just running around the suburban streets test driving) ? There just so happens to be a C250D (non turbo OM605 with 722.3xx trans) at Imlachs I could souvenir the fan off.... I wouldn't be so stingy re water pump.

[Bartman4800]

Can you feel (or measure) the temperature of the intake and outlet hose of the radiator? If there is flow, they both should be hot (when the engine is hot), with the outlet hose slightly cooler.

If these hoses do not heat up, there must be a blockage in the cooling system.

The whining noise can be water pump or alternator. Take the belt off and feel for play and a buzz when spinning. A dead fan is only compromising cooling when the vehicle is stationary, not when it is driving.

Are you sure there is no airlock in the system? And also do not dismiss the thermostat. I have seen thermostats that were faulty out of the box.

[tsharkey]

Thanks Bart - The upper hose was hot but the plastic impellor on the water pump shattered (4,000 RPM, who would have thought) and not much water was being pumped around. Just glad it happened to me giving it the italian tuneup, as my partner (who drives it 70kms on a freeway each day) could have been stranded with a cooked engine .... Gota new belt tensor pulley while everything was out

[Bartman4800]

Thanks for the reply and good to know!

[CraigB]

So solved with waterpump. I have an identical thing happening on the landrover 300tdi. Can drive it on hot or cold days and rev it up etc and the gauge sits dead in the middle. But if I have a trailer on or push it for prolonged periods under load (like the climb on the freeway through the tunnels last Friday, and the temp rises. It can get into red and even stay there (eg. when I was towing a car and not really anywhere to pull over) and it never seems to boil, and if you coast down a hill not under load, it doesn't take long to come back to that middle point. They have a set up with radiator cap not on radiator and hard to see if anything flowing. I have a water level alarm in the top of the radiator and in recent times I was wondering if I had a problem with head gasket when I kept getting air in top of radiator. I put a pump to raise pressure on the cold system and found a couple of the higher radiator hoses leaked - tightened it and has been fine since.

My logic was that if thermostat and radiator restricted flow, then would it cool down so quickly once you took the extra load off the motor. Probably worth replacing pump and thermostat and having radiator flow tested, but annoying that it works so well 90% of the time.