Mercedes OM 636 overheating

[kingsebi]

I changed the thermostat on my OM 636 (found one that fitted the three hoses in the previous owners spare box) and now the motor overheats.... One time it ran a good ten minutes because I had to get out of a small anchorage. When I turned it off the needle of the temperature gauge was at maximum.

Now I'm scared the head gasket went. How do I know? There is no water in the oil. The motor starts and runs normally, but when the temperature goes up it doesn't stop at 80 degrees celsius but goes past 90 and then I shut it off to prevent further damage. That happens in the course of ten minutes.

How can I rule out that it's the head gasket?

I can't source a thermostat. Is there a way to do without?

I put the thermostat in boiling water to test it but saw no change. Does this mean its not working?

The arrow on the thermostat has to point away from the heat exchanger, right?

Edit: The raw water side of the cooling system seems fine, there is plenty of water flow.

Edit2: After I shut it down I open the heat exchanger pressure cap and cooling liquid pours out.

 

[PaulRainbow]

You fitted a stat that you found in a box and now the engine overheats ?

The stat doesn't open in boiling water ? Perhaps it was put in the box because it failed and a previous owner kept it as a spare, bizarre but it happens.

Why did you change the sat ?

Does it overheat without the stat ?

What's the significance of the item in the picture ?

 

[kingsebi]

The item in the picture is the thermostat. I changed it because the old one leaked water. I don't have a fitting T-piece to try without the thermostat. Or how would I try without? Unfortunately I already threw away the old one... very very stupid

Can I fix the thermostat I have somehow?

 

[Boater Sam]

So it didn't overheat but you had a leak which replacing the stat with one of unknown status from the previous owners junk box cured but now it overheats?
Probabilities,
1 The replacement stat was duff which is why it was in the box, unmarked, unboxed.
2 You have introduced an air lock in the cooling circuit which is preventing flow in the engine cooling system.
3 Both of the above.
4 Letting it overheat repeatedly has damaged something, may be the head gasket ( unlikely if you are lucky )

 

[kingsebi]

Yes exactly. Ok I understand. Can I fix the replacement thermostat? How can I get rid of the airlock in the cooling system?

 

[PaulRainbow]

The item in the picture is the thermostat. I changed it because the old one leaked water. I don't have a fitting T-piece to try without the thermostat. Or how would I try without? Unfortunately I already threw away the old one... very very stupid

Can I fix the thermostat I have somehow?

My previous boat was fitted with an OM636, but the t piece didn't have a stat in it, the stat was in the head.

I'd suggest calling Manfred at westfield 4x4 MERCEDES-BENZ OM 636

 

[PaulRainbow]

Yes exactly. Ok I understand. Can I fix the replacement thermostat? How can I get rid of the airlock in the cooling system?

Given your description, i would ignore the airlock comments in post #4. It's practically impossible to airlock an OM636

 

[kingsebi]

Ok thanks. I wrote Manfred an email. Will see what he says. Unfortunately he has no such thermostats in stock. I sure should have kept the other one even though it was leaking water. Is there no way I can fix the one I have?

 

[PaulRainbow]

This might fit Billet Inline Thermostat Housing with Genuine VW Coolant Thermostat

 

[kingsebi]

Wow thanks alot that looks like it! I would need the 80 degrees variant right?

 

[mil1194]

I would suggest one thing - the stat that does nothing is IMHO junk if it didn’t do anything when tested in the boiling water. Is it stuck open or closed? I would try running the engine without a stat at all and keep an eye on the temp gauge. In theory it will just take longer to get warm/hot and it may be that it gets to the correct temp and stays there. That would eradicate any worries about further damage that has/hasn’t been caused.

 

[kingsebi]

Thanks for the suggestion. I have ordered a new thermostat now, the one PaulRainbow suggested, Manfred from Westfield 4x4 confirmed that it might be ok. So I will try with the new thermostat in a couple of days...

 

[roaringgirl]

You picture shows a housing, which we assume contains a thermostat. Presumably it's the housing that is leaking on the other one. Perhaps it's possible to remove the good thermostat from the leaky housing and install it in the good housing?

If you put the whole housing in a pan of water to test, of course you saw no change: the thermostat is inside!

If you want to start afresh, any housing with the same entry and exit points will suffice, along with any thermostat that fits it, with the correct temperature rating.

 

[kingsebi]

Unfortunately I threw away the old housing (with the thermostat inside) so that is not a possibility.

The thermostat is inside, but it still gets into contact with the hot water, no? I looked inside the housing and saw no change on the thermostat, that's what I wanted to say.

Now I ordered a new one, will try in a couple of days. I just hope it's not the head gasket.

 

[kingsebi]

Ok, so while the parts are on the way (I'm getting more and more sure that the EU put out a directive after Brexit to hold UK goods in customs for ridiculous amounts of time - record is two months last year in Italy - thus harming companies from the UK) I tried to run the motor without the thermostat (that was stuck closed, so obviously no water flow) as mil1194 suggested. Unfortunately the housing of the thermostat is non opening so I had to jerk it out with brute force. Anyway the motor ran for half an hour without overheating. I thought there was a funny smell but maybe I'm just getting paranoid. After I checked coolant and oil. Coolant level was unchanged and no oil in coolant. No coolant in oil either, so I suppose I was lucky and got away with overheating the engine a couple of times... Thanks for helping me out!

 

[kingsebi]

I wonder if I can use the motor without the thermostat for a month or two? It's mostly for anchoring. Will this harm the motor?

 

[PaulRainbow]

I wonder if I can use the motor without the thermostat for a month or two? It's mostly for anchoring. Will this harm the motor?

If you remove the faulty stat you can use the engine, it will just run a little colder than normal.

 

[kingsebi]

Ok thanks. That it runs a little colder in the beginning is what I observed as well. That won't do any harm? Which would lead to the question - why is there a thermostat in the first place?

 

[Skipper_Christoph]

I wonder if I can use the motor without the thermostat for a month or two? It's mostly for anchoring. Will this harm the motor?

No problem using the motor for a few minutes while anchoring. I doubt it would get up to temperature in this short period

 

[kingsebi]

Thanks christoph. Actually got up to temperature quite fast. Without the thermostat a little slower. Once warmed up the temperature is the same as it was - that does make sense right?