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 12psi. 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 put the viscous fan back on. At the same time a new Nissens, radiator was fitted. With a Mercedes water pump, thermostat and viscous fan clutch.

But 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.

I feel the issue is lack of coolant flow as the viscous fan will never kick in. Also, I have tried locking out the viscous fan and it still over heated. A long reach radiator cap helped to stabilise the temperature a little.

The only way to keep the motor cooler is by fitting a drilled thermostat. The engine still starts to creep up to hot but is generally running cooler with this setup. Again this goes with my ‘lack of coolant flow’ way of thinking.

I have done A Liqui moly coolant flush on it but the water came out clear and it made no difference.

I am about to fit new coolant hoses as I thought they may be collapsing at high rpm, thus reducing flow.

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

Something's u just live with...

Lemme clarify though, at this point your saying it will just creep over halfway on the heater gauge when going up long high rpm hills?

At this point can you keep it below or equal with 2/3 mark on the guage, without turning the heat on full blast etc?

__________________

What is the water to coolant ratio? 70 percent water/30 percent coolant would offer better heat exchange than 50/50 IF it offers enough freeze protection for your situation.

RedLine Water Wetter is an emulsifier added to the coolant that improves heat exchange, it does help.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

X2 - Water Wetter will help.

BR:

It would seem that in increasing the engine's output, that simultaneously there has been an increase in rejected heat. That rejected heat must 1) be carried away by the coolant, and 2) be dissipated into the airstream by the heat exchanger (aka, radiator).

Area #1, coolant flow perhaps should be checked first. There is a re-circulation, or by-pass circuit, the principal function of which is to provide quick warmup. The thermostat simultaneously controls flow in the by-pass and through the radiator. As flow is increased in the radiator, it is decreased in the by-pass. That a drilled thermostat caused a reduction of temperature suggests this test:
Remove the thermostat and arrange a plug of the by-pass circuit. In this configuration coolant flow will be 100% thru the radiator.

If the above suggested test, perhaps in combination with a low concentration of anti-freeze, and addition of Water Wetter surfactant, does not have the desired effect, then attention to the heat exchange and air flow will be in order.

It would fully overheat if I didn’t back off the throttle on big long hills. When up big mountain roads and fully loaded I would have pull over to let engine cool. Now with drilled thermostat, I haven’t got a long hill long enough nearby to make it get near the red, but feel it still would. As the gauge creeps up and no cooling comes in, even though brand new and checked to be operational.

You have an oil cooler and it is functioning properly?

Do you have a working electric coolant fan?
If you do not have one at all that adding one could help but of course it does not get to the cause of the issue.

If you added on the Turbo you likely don't have that over boost protection that is on the models made for a turbo.

Is there difference between NA Engine and the turboed Engine?

__________________
84 300D, 82 Volvo 244Gl Diesel

Is the temp gauge definitely accurate? Confirm tstat opening temps with an infrared thermometer.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

A couple of questions:


1) Can you explain what you mean by a "long reach" radiator cap?


2) Would it be possible to measure the temperature at the engine water inlet and outlet when this is happening? Use an IR thermometer is fine, all I'm looking for is the temperature differential.


3) Is it possible to mount a pusher fan in front of the radiator?


4) Is there an oil cooler? If so, what is the inlet/outlet temperature?

Extra fuel,extra air,extra load,with same cooling and exhausting capacity as N/A engine?

Im leaning towards the radiator being too small for the turbocharged engine. Its heat soaking. Imo

I'd like to hear a little more about the problem, but I'm thinking that the answer may lie in the oiling system. it could be that the little thermostat in the oil filter housing isn't working. Or that the oil cooler, if one is even present, is inadequate. At one time, there was a little oil cooler fan system available for hot climates. something like that may work here. Like this:

https://www.ebay.com/itm/04-06-Mercedes-W211-E55-CLS55-AMG-Supercharged-Oil-Cooler-Fan-OEM-2115000400-/123831141668

Yes, it has an oil cooler attached to the right hand side of the radiator. I have no idea if working. Is the best way to test just to see if warm all over once engine up to temp?

It spits coolant out of rad if it gets too hot on the gauge so presume it is accurate when saying it’s hot.

Put a IR thermometer on the thermostat housing when it still had a standard stat in and at one point it was 110c on one side and 70c on the other.