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Discussion Starter #1
So the 164 saunters through its MOT apart from a directional tyres swapsie and all is well in the world. The revs have settled down, diagnosed as a loose temp sensor by Ian at Mobitech, but now my coolant seems to be going walkabouts.

The loss seems to be very minor, like 1/4 of the expansion tank a week under normal driving conditions.
I left the car for 2 days with a square of tarp to try and locate roughly where it was coming from but to no avail.

So what have I broken this time?
 

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Hard to say. The first thing is to find out whether there's a decent amount of pressure in the cooling system. When the engine is hot, do the hoses feel hard? Is there a rush of escaping air as you slacken off the cap on the expansion bottle? (usual "never-run-with-scissors" cautions apply when it comes to that)!

It's possible you have a tiny weeping radiator tube or joint somewhere. The heat (especially in this weather) will mean it evaporates before you can spot it.

Make sure the oil level isn't going up and the oil isn't emulsified or the cam covers full of "mayonnaise" (that'll be head gasket).

Make sure the little hoses at the back of the water pump (or the pump itself) aren't weeping, and (is it a 12-valve?) the water hose to the heated throttle body.

Lastly, is there that sickly smell of warm antifreeze when you turn the heater on? (heater matrix).
 

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Discussion Starter #3
Yeah its a 12v.
I can't test the heater as the fan gave up on me about a week after I bought it, plan to fix that after the warmth has left us.
There seems to plenty of pressure in the system and no signs of mayo anywhere.
All the hoses seem in fairly good condition which is why I thought I'd check on here.
Hopefully its just something stoopid that I'm missing but you never know.
 

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you can try filling expansion bottle with water so it starts dripping out. Start engine in idle. Do you see bubbles coming out? If no try to rev it a bit and keep looking at bottle while reving. Its to do both but possible :D
If you see them then the head gasket went.
 

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If the hoses all seem good try the following areas.

If still an original radiator its probably leaking at the top left corner where the core meets the plastic ends or simply dissintegrated somewhere behind the AC condensor due to age. If your AC is'nt working its easy to take the condensor out and check the Radiator, but make sure there is no gas at pressure in the system!!!.

There seems at least in the US to have been an issue with replacement non-OE expansion bottles which crack at the lower seam, again not obvious without removal. Put some card or similar under the tank and see if any is leaking from the underside.
 

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Discussion Starter #6
Well I've traced the source to around the pump area, the reason for the lack of puddle seems to be that its collecting on the sub frame.
I would assume its not the pump itself being its the earlier metal impeller type so hopefully its something little (read cheap).

I'm going to have to wait a few days before I can get it on a ramp so I'll just top up as I go.
However the bonnet hinge decided it would be HILARIOUS if it spat its pin out leading to much joy fighting the hydraulic rams to get the thing back in position and lock.
 

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Could easily be the pump shaft seal leaking - that's the most common failure mode for any pump. The impeller type doesn't affect the bearing life. Had a pump seal go on our old 164.
 

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More than likely what Chriss says but pull the hoses off the pump and check the condition of the connecting pipes. They can oxidise and flair up causing a bad seal.
 

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Testing head gasket is really easy.:
Cherck following

Oil in coolant
Check under cap where you pour oil in for white stuff
Fill your expansion bottle over the top start engine and rev it a bit plus watch expansion for bubbles while reving

In my case it was head gasket
 
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