Really stumped on a turbo'ed om602 overheating issue

[Brightonrider]

I would appreciate some help on an overheating issue I cannot seem to rectify.

Some background:
We have a Mercedes 410d based motorhome with an om602 2.9 and it was originally NA when we first bought it. I did a lot of research and found these were quite commonly turbo charged a few years ago and I know personally a couple of vans my size, or heavier, that have had it done for years with no overheating issues, or any issues at all.

So this is what I did, turboed it. A new turbo and custom manifold was fitted alongside a Diesel Pump UK modified fuel pump with 6mm elements to provide the extra fuel under boost. The oil pan was tapped for the turbo oil return, the boost piping made up and an intercooler added. I also added 16" tyres and a hi-ratio gearbox to bring down the cruising RPM's. The end result has created a lovely smooth and powerful drive. The motorhome will now still comfortably at 75mph on the motorway and is not crawling up hills like when it was naturally aspirated. There is a very very light haze of diesel smoke under strong acceleration and I am running a modest boost of 10psi. It drives really well and starts in the button.

The overheating issue was found on our first 'turbo-powered' voyage to Italy. Van ran great but I was finding long hills were making the temp gauge rise above white middle mark. I could generally control the temps by putting on the heater and backing off the accelerator. But obviously something wasn't right as left unchecked the van would fully overheat. At this point we were running just on an electric cooling fan thermostatically controlled. The original viscous clutch fan had not been refitted as I had been advised the electric would be 'far superior'.

So cutting a long story short we returned to the uk and I did some changes to the setup by adding a larger intercooler, with more airflow and also removing the electric fan and putting the viscous fan on. At the same time a new Nissens, radiator was fitted. With a Mercedes water pump, thermostat and viscous fan clutch.

Put the van still continues to run too hot going up hills. I never allow it to go too near the red on the guage as not to damage the engine. As soon as you pull over or get on the flat the temps drop straight back down.

One thing I have noted is that I don't think I can hear the viscous fan cutting in when the engine is warm/hot. So I removed the new viscous clutch and bench tested it by warming the metal strip which should lock out the clutch. The strip expands but the clutch did to lock up or add any resistance.

So, I purchased another Mercedes fan clutch and put that in tonight, assuming the other to be faulty, and again the van got too warm up the hills. There was a lay-by at the top of the hill and I pulled in quickly shut off the engine and tried to spin the fan, it had very little resistance. I was expecting it to have been very hard to move with the engine being at such a warm temperature. I know it is not just the gauge running hot as hot water started to come out of the radiator overflow pipe whilst I was on my back checking the fan resistance.

My next plan was to lock out my other viscous clutch to see if the engine temperatures would be controlled with a permanently engaged fan. Ideally I don't want to it as I was sending it back to Mercedes under warranty to have it tested and I would lose the money.

So looking for some advice - what have I missed or what can I test next.

 

[LostKiwi]

First thing - where is the intercooler placed? The intercooler is a source of heat. If it's in front of the radiator it reduces the ability of the radiator to transfer heat from the engine. Bearing in mind you're now burning more fuel which in turn makes more heat and you're getting a double whammy. I had a similar issue on my Defender when I fitted a hybrid turbo, cranked up the pump and fitted a full width intercooler mounted in front of the main radiator. Going back to the standard side mounted intercooler sorted the overheating. The eventual fix was simply a higher efficiency larger intercooler mounted next to a thicker radiator with more cooling cores. A larger radiator may be beneficial in your case too.

As for why your viscous fan doesn't work that's another question. Is it mounted behind the electric fan? If the electric fan isn't mounted right up against the radiator it may not be drawing hot air through the radiator.

One other thing - is the electric fan blowing the right way? Silly question but it wouldn't be the first time.

 

[Doug1234]

Are you monitoring oil temp ? , do you have an oil cooler fitted ?.
Check engine timing ?

It may be passing excess heat from engine oil across to cooling system.
My old 1990 w124 300d after having a new rad could be made to run hotter(not overheat) but temps go up by nearly 8 or so degrees just by holding a higher speed for five minutes or so in hot summer weather, these were shall we say a bit over the speed limit but it proved the new cheap rad I had fitted only just coped with dispersing the heat.
Are there any different rated thermostats for this engine ie something usually like 87 or 92 degrees ?

 

[Brightonrider]

Thanks for the replies.

LostKiwi:
Intercooler is approx 4" away from the rad and covers 1/2 of it. There appears to be plenty of airflow around it. Originally I had a smaller intercooler away from the flow of the rad and moving the larger IC in front of the rad made no difference, positive or negative, to the heat issue.

Electric fan - it is not fitted. I wanted to ensure the viscous cooling was working correctly before adding any additional cooling components.

Viscous clutch - well this is quite telling - I did some more bench testing and the original (but only 6 months old) Mercedes VC would not lock up when heated. I had a new OM606 VC and fan (non Mercedes part) that I had in the garage so I bench tested this and it locked up strongly when heated. With this in mind, I removed the new 2nd Mercedes VC / fan, and fitted the OM606 VC and fan. It required a some spacing and very minor trimming of the plastic blades but otherwise fitted well. I then took the van out for a test drive. Same story - on inclines of any length the temperature starts rising again.

So, I jumped out on the next pullover and felt the pipes and radiator. The radiator did not feel hot and the lower the rad pipe was barely warm. So, this would explain why I cannot hear the fan kicking in - the radiator is not getting hot enough to heat the VC to engage the fan.

I have a laser temperature gun and the top hose read up to 75C but the rad barely read 50c and got colder the lower down I tested. The lower hose was approx 40c.

So, why would the water temperature overheat yet the radiator not be hot? Some kind of blockage?

Other things I noted - when checking the coolant level - there was, what looked like, calcium deposits on the rubber seal of the radiator cap. I wiped it off and after the road test checked again and there some more deposits on the rubber seal.

I have read about a citric flush that mercedes perform to clear the water way internals, is this worth a shot?

 

[Blobcat]

Sounds like your internal waterways are blocked...

 

[star]

If you can control temp by use of heater, then you rad is too small also Have you looked into a different sized water pump pulley, ie smaller diameter this pumping more water? Putting the inter cooler in front of rad won’t help as it will be feeding the water rad with heated air. (F1 cars pull out of slip stream to cool the car)

 

[Uncle Benz]

Traces of something on the rad cap worry me. I’d be performing a test for combustion gasses in the cooling system first. It’s possible the higher cylinder pressures may be overcoming the seal of your head gasket. At the end of the day you have asked your previously stock engine to provide more power. An inevitable by product of this is going to be an increase in thermal stress. It’s going to expose any weak links very quickly. Ultimately a larger radiator may be the right answer, but it is worth ensuring the fundamentals are all good first.

 

[Uncle Benz]

If you can control temp by use of heater, then you rad is too small also Have you looked into a different sized water pump pulley, ie smaller diameter this pumping more water? Putting the inter cooler in front of rad won’t help as it will be feeding the water rad with heated air. (F1 cars pull out of slip stream to cool the car)

I like your thoughts Ian, but I’ve long been wary of smaller pulleys and trying to pump the coolant faster. You need the water to spend enough time in the radiator to actually cool. Moving it faster won’t necessarily gain anything if the radiator capacity is insufficient. To my mind a larger radiator is a better step than moving the coolant faster.

 

[Brightonrider]

Sounds like your internal waterways are blocked...

Is there anyway of testing for this? Is the critic flush the best option if blocked?

 

[Brightonrider]

Traces of something on the rad cap worry me. I’d be performing a test for combustion gasses in the cooling system first. It’s possible the higher cylinder pressures may be overcoming the seal of your head gasket. At the end of the day you have asked your previously stock engine to provide more power. An inevitable by product of this is going to be an increase in thermal stress. It’s going to expose any weak links very quickly. Ultimately a larger radiator may be the right answer, but it is worth ensuring the fundamentals are all good first.

There are no combustion gasses in the coolant, this has been tested for at the garage that fitted the new radiator, pump and thermostat.

 

[Brightonrider]

If you can control temp by use of heater, then you rad is too small also Have you looked into a different sized water pump pulley, ie smaller diameter this pumping more water? Putting the inter cooler in front of rad won’t help as it will be feeding the water rad with heated air. (F1 cars pull out of slip stream to cool the car)

If my rad was too small, wouldn't it be too hot all over instead of cool?

 

[LostKiwi]

Try running this through:
https://www.amazon.co.uk/dp/B004QI7YI8/ref=cm_sw_r_other_apa_i_72t3EbTWY7P9R

How old is your thermostat and water pump?

 

[Uncle Benz]

Absolute curveball thought! It’s entirely possible on an om602 to fit the belt incorrectly, and run the waterpump backwards. They overheat easy then! I’ve seen this twice in my time

 

[Brightonrider]

Absolute curveball thought! It’s entirely possible on an om602 to fit the belt incorrectly, and run the waterpump backwards. They overheat easy then! I’ve seen this twice in my time

 

[star]

Absolute curveball thought! It’s entirely possible on an om602 to fit the belt incorrectly, and run the waterpump backwards. They overheat easy then! I’ve seen this twice in my time

good one, seem it on a 272 engine too

 

[Brightonrider]

Weirdly, I was thinking about the belt today, as it makes slight loose flapping noise at idle. I actually made a video of it:

The belt feels tight when not moving but I thought it looked, and sounded, a little loose when in motion. Does that look right?

Also, can you see whether the belt is correct from the video?

Also, is there something missing in the ringed zone - looks like there is a threaded bar but nothing attached:

 

[Uncle Benz]

Should be like this. Long shot, but you never know.

 

[Brightonrider]

Try running this through:
https://www.amazon.co.uk/dp/B004QI7YI8/ref=cm_sw_r_other_apa_i_72t3EbTWY7P9R

How old is your thermostat and water pump?

Water pump is 5 hours old and thermostat was checked to be operational and was either replaced or refitted because ok. Will ask mechanic tomorrow.

 

[Brightonrider]

Should be like this. Long shot, but you never know.

Thanks for that.

I can see you're not too far from me. Can you recommend a decent local merc mechanic that could accommodate a 7m motorhome?

 

[Uncle Benz]

Thanks for that.

I can see you're not too far from me. Can you recommend a decent local merc mechanic that could accommodate a 7m motorhome?

Ha! Not me I'm afraid! GL's and R Class hang out the doors when they are on my lifts!

I think Cole at MBS can handle big stuff, but they are a bit of a trek in Southampton.