Really stumped on a turbo'ed om602 overheating issue

[Brightonrider]

OK thanks for the info.

One final video I took. When squeezing the bottom radiator pipe, the thermostat housing would make a rattle / clinking should in time with each squeeze, would this indicate anything wrong?

 

[Uncle Benz]

That's the tiny little bleed valve rattling. Completely normal

 

[Brightonrider]

OK, I'm going to double check the belt, but from the video and pics I have, I think it looks fine.

I think it's worth doing a coolant cleaner flush in the system seeing as it's nearly 29 years old and it had little particles on the rubber seal of the rad cap. Is the citric flush seen as too harsh? Any other product recommendations or ones to avoid for this engine? Amazon seems to have quite a few options.

 

[Doug1234]

You mentioned lower part of radiator is cooler, therefore the radiator is doing its job... thermostat is either knackered and not working correctly or fitted the wrong way around.
Thermostat is the gateway back into the engine so coolant flow is being slowed down by the thermostat not functioning correctly. Most likely it is slightly open which is why you can still run and drive but any extra load overheats the system.
To me that toggle rattles to easily so I can only presume coolant is flowing both ways when hose is squeezed, check if it still as noisy when engine is cold.

 

[clarkmichigan55b]

Hello,
1. Just go back to when you first had the vehicle when it was naturally aspirated did you have any overheating problems then or have these happened since the added turbo and 16inch wheels ?

2. When the temperature gauge starts to go up does the needle start to occasionally twitch?.

3. The temperature gauge should be in the middle or a needle width above the middle on normal flat running but is quite sensitive to temperature changes.

4. Is the radiator fan shroud complete or has this been hacked about resulting in air flow being misdirected from the viscous coupling fan.

5. If you have the old viscous coupling i think there is a tab you can bend over to permanently engage the fan. i will have to look at my engine manual to check this.

Adrian.

 

[Brightonrider]

Hello,
1. Just go back to when you first had the vehicle when it was naturally aspirated did you have any overheating problems then or have these happened since the added turbo and 16inch wheels ? NO OVERHEATING BEFORE THE CONVERSION. BUT THE TEMP WILL STILL RISE EVEN IF THERE IS LITTLE TO NO BOOST (I HAVE A BOOST GAUGE) SO DON'T THINK IT IS DUE TO THE TURBO'ING.

2. When the temperature gauge starts to go up does the needle start to occasionally twitch?. NOPE

3. The temperature gauge should be in the middle or a needle width above the middle on normal flat running but is quite sensitive to temperature changes. IT WOULD GO ALL THE WAY TO THE RED IF I DIDN'T LET OFF ACCELERATOR

4. Is the radiator fan shroud complete or has this been hacked about resulting in air flow being misdirected from the viscous coupling fan. COMPLETE

5. If you have the old viscous coupling i think there is a tab you can bend over to permanently engage the fan. i will have to look at my engine manual to check this. I 'FEEL' THE ISSUE IS DOWN TO POOR CIRCULATION - THERE JUST ISN'T ENOUGH HEAT IN THE RADIATOR TO ACTIVATE THE VISCOUS FAN.

Adrian.

 

[Brightonrider]

You mentioned lower part of radiator is cooler, therefore the radiator is doing its job... thermostat is either knackered and not working correctly or fitted the wrong way around.
Thermostat is the gateway back into the engine so coolant flow is being slowed down by the thermostat not functioning correctly. Most likely it is slightly open which is why you can still run and drive but any extra load overheats the system.
To me that toggle rattles to easily so I can only presume coolant is flowing both ways when hose is squeezed, check if it still as noisy when engine is cold.

I will test the thermostat again. One thing to note is - the heater gets hot very quickly from a cold start. Would this indicate anything? I seem to remember it took quite a while to get warmth from it, pre overheating issue.

 

[Doug1234]

Heater getting hot from a cold start is normal ....until the thermostat opens the coolant will be flowing through the heater matrix as long as you have selected heat, if you haven’t then coolant in block just gets warmer until thermostat opens and it allows the hot to flow out to radiator and cooled water to enter from radiator back into engine.
Now if thermostat is not functioning properly then heat output from heater with be quite fierce in a short time but most owners on here will be familiar with how quickly even warm air is available on cold mornings for defrosting screen

 

[clarkmichigan55b]

Hello,

I have enclosed a page from my manual on locking up the viscous coupling fan.

The enquiry in the needle twitching, i had the head gasket fail which tied up with the needle and excessive pressure in the cooling system.

 

[Brightonrider]

Thanks for the replies so far. It has back in the garage and these are the findings:

- I put in a Luqui Moli coolant flush before dropping off at the garage. It was left in for 12 hours and the water that came out was spotless.

- The brand new OEM rad cap doesn't seem to allow the system build pressure. After further investigation there is a longer and shorter version of rad caps. Currently one of the mechanics has brought in one of his own caps that fits and appears to be allowing the engine to build pressure better. It looks to have stabilised the amount the temperature needle swings around but the van still overheats on hills with it on. One of the issues is Mercedes don't make the radiators so this may cause an issue with the OEM rad cap. It's a good make rad, Nissins.

- The whole system was pressure tested and lost no pressure.

- There was a huge temperature difference across the thermostat inputs / outputs when tested after a long hill pull, but the lower rad hose is still cool.

- The thermostat is opening when tested in boiling albeit very slowly and not a huge amount. When tested with blow torch it opens up considerable more.

- The garage then did 4 small drill holes in the thermostat:

The result = no more overheating. The needle did fluctuate more than previously, which is understandable as the cooler coolant will now get through.

So the garage put a brand new thermostat in just to make sure the original 'drilled' one was not faulty. The different longer rad cap was fitted at the same time and they wanted to see what had had the greater effect. The new thermostat caused the van to overheat again.

So, the only thing that now prevents over heating is the drilled thermostat. A quick google of drilled thermostat and this seems to be quite common place to control overheating.

Any thoughts welcomed.

 

[bembo449]

I was expecting a waterpump problem

 

[Brightonrider]

I was expecting a waterpump problem

It's new and it replaced a new non-merc one. So unless they are both kaput, think I can rule that out.

 

[oigle]

You mentioned you had an infra red temp gauge. Have you actually measured the temp at the thermostat housing to see what the actual temp is when "overheating"? How does it compare with thermostat opening temp?
By drilling the thermostat, you are destroying its use - slower warmup and too much temp variance. Not good for engine.


Ian.

 

[LostKiwi]

Sounds to me like the wrong thermostat. Are you fitting the standard one? If so it may have an operating curve unsuitable for your modification. You need one with a faster operating time.
Have you tried looking at the thermostat from a turbo diesel?

 

[Brightonrider]

Sounds to me like the wrong thermostat. Are you fitting the standard one? If so it may have an operating curve unsuitable for your modification. You need one with a faster operating time.
Have you tried looking at the thermostat from a turbo diesel?

The thermostat is the same one for the later turbo charged t1's. I can't seem to find a lower temperature one anywhere.

Do you think a citric flush is worth doing on this engine? As a motorhome only gets used a few times a year and is no 27 years old, maybe internals have flurred up causing restricted flow. I have already done a liqui moly flush is a citric flush stronger?

 

[LostKiwi]

No idea on flushes.

What is the existing thermostat rated at?

 

[LostKiwi]

Thinking about this more it sounds like a flow problem where you aren't getting enough water through the radiator. Drilling the holes or using the heater helps the flow and aids cooling.

 

[tode]

If I've read this correctly, the only thing you haven't checked is the radiator itself.
We had an overheating problem (on a truck) whicch turned out to be small bits of broken-up O-ring stuck in the top of the rad tubes.

 

[Brightonrider]

No idea on flushes.

What is the existing thermostat rated at?

85c

 

[Brightonrider]

If I've read this correctly, the only thing you haven't checked is the radiator itself.
We had an overheating problem (on a truck) whicch turned out to be small bits of broken-up O-ring stuck in the top of the rad tubes.

It has a brand new Nissens radiator fitted.