Coolant Loss and Thermostat

[jonsowman]

Hi all,

I know there have been quite a few threads on this but I'm rather new to cars so could do with some help.

My 406 loses coolant gradually, needs topping up every 1-2 months. I've searched and found this could be the bottom rad hose or the thermostat housing. Attached is a picture of the bottom drivers side of my rad -- are these deposits symptomatic of a leak here?

I'm also finding the engine is running cooler than it should be -- at 70mph cruise on the motorway the engine is only just above 70C (on the gauge). This forum seems to say this could be thermostat failure. I took the car for a short drive today and stopped when the temp gauge reached 70C. After this, the rad and rad hoses were warm, am I right in thinking this shows the thermostat is broken, as coolant shouldn't go via the rad until the engine is up to ~90C?

Where is the thermostat on the 2.1TD?

Thanks for any help

[gumby6371]

Assuming the layout of the 2.1 is pretty similar to my 1.9 the thermostat is under the fuel filter housing along with the fan connectors. I changed mine recently following a head gasket leak as they don't seem to like being coated in oil so I'd check your coolant is clear while I'm at it.

[Parm]

Looks like ur radiator may have a slow leak, but u cud try radwell or a.silver packet of radiator cement that u pour into ur radiator or coolant to stop any leaks. I would try that first n see if there's any difference. Could be the hose may be perished a bit perhaps?

[jonsowman]

It is definitely a slow leak, I can never find coolant leaking, so it must be so slow that it evaporates. I notice when the engine gets too warm (90+) it will definitely dump some coolant. Does this provide any further evidence as to whether it's a hose or the rad?

Is it possible that when the coolant got low, some air got in, and now there's an airlock? Am I right in thinking air in the system would cause additional pressurisation which could be increasing the coolant loss problem? If so, I guess I just need to open the coolant bleed valve and release the air?

Lastly, the thermostat. Does it sound like it's gone? Has anyone got a diagram of where to look, Haynes says "On 2.1 turbo diesel models, the thermostat housing is mounted onto the rear on the cylinder block on its right hand end". I've had a poke around but I don't really know what I'm looking for!

Thanks for your help

[poddack]

From experience on my 2.1, your bottom radiator hose probably needs replacing. It will leak where it connects to the radiator and the metal flange rusts so it's not able to make a good seal.
Over the last 3 years my engine has run at about 70.c also, i'm not sure there's a problem. It might be a good idea to check that your cooling system is bled properly.

[poddack]

The thermostat does indeed live at the back where the bottom radiator hose connects to the water pump.

[jonsowman]

Thanks poddack.

I will bleed the cooling system and see if there's an airlock in there somewhere. Where are the bleed points on the 2.1?

It does indeed look like the rad and bottom hose are going to need changing, they're not in the best of shape and getting rid of this annoying coolant leak would be great.

Does the engine running cooler than it should cause any harm?

Thank you for your help

[teamster1975]

Does the engine running cooler than it should cause any harm?

It'll probably use more fuel as it's not getting up to temperature, but to be honest I fitted a new thermostat to my 2l petrol and it still ran an 70-80 so I wouldn't worry too much.
I would change the thermostat as a matter of course, don't forget a new o-ring for it as these go very manky with age as mine did!



You can bodge the bottom hose by cutting a good conrad fitting from a donor top hose and attaching it with a bridging pipe & some jubilee clips.

[jonsowman]

Very helpful of you mate, cheers.

I'm going to grab HimBigChief's (1 year old) radiator and bottom hose as he's breaking his 2.1TD, so that's fine. I'll replace the the thermostat whilst I'm at it.

Appreciate the help guys