Coolant leak tdi90

steve@cromford

steve@cromford

A2OC Donor
Coolant level warning light came on over the weekend, after driving from Leicester to Norfolk. It took almost a litre to get level up to max. The next day it had lost about the same amount after driving about 20 miles. Topped it up yesterday before returning home to Leicester and it’s dropped to just above the outlet pipe at the bottom of the filler tank. Coolant temp remained a constant 90degrees for the journey and warning light hasn’t come on again. Aside from routine flushing at servicing intervals I’ve never needed to top it up at all. It’s clearly not gushing out and there’s no obvious sign of where it’s leaking, there was only a slight patch of coolant under the car from being parked overnight. There’s a small amount of coolant sitting on the undertray behind the radiator.
I can’t get the car to my garage until next Wednesday. Any obvious things I could check for?
Thanks in advance
Steve
 
Check the 2 pipes that run along the underside of the tandem pump across to the oil cooler. Leaking tandem pump diesel causes them to perish and leak water under pressure.
 
Does a 90 have a steel cooling pipe across the front of the engine? It is quite low down. These rust from the outside in and the weep coolant. Worth checking for damp rust patches.
 
6987BED3-491B-4586-BE4E-DEEE39610406.jpeg

Courtesy of Tom's rebuild. I'll draw an arrow on it now for you :)
 
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The green arrow is pointing to the tandem pump, the red arrow to the oil cooler pipes. Where they run underneath the tandem pump they can have diesel dripping on them which will cause them to perish and leak. A very common problem with coolant leaks.
 
Also check the condition of the water pump - when it was changed also. I had a very similar experience and it seems that a weep hole had opened and allowed the coolant to drip out of there, but only when the engine was running - there was no pool under the car when stood. Took me a few weeks to pinpoint it, which I did when doing a routine cam belt service a few years back.

Water drips around the belt area and is thrown around in the warm environment and rarely pools, leading to a hard time diagnosing the leak.
 
I think you can add a tracer dye to coolant? BUt given the two randem pumps I have done recently there are about 4/5 connections under it that get swamped in deiesle and oil mist. Like a balloon festival under there if its not been cleaened and leaking for a while.
 
A2Steve said:
The green arrow is pointing to the tandem pump, the red arrow to the oil cooler pipes. Where they run underneath the tandem pump they can have diesel dripping on them which will cause them to perish and leak. A very common problem with coolant leaks.
Click to expand...
Thanks Steve
will take a look
 
Skipton01 said:
Also check the condition of the water pump - when it was changed also. I had a very similar experience and it seems that a weep hole had opened and allowed the coolant to drip out of there, but only when the engine was running - there was no pool under the car when stood. Took me a few weeks to pinpoint it, which I did when doing a routine cam belt service a few years back.

Water drips around the belt area and is thrown around in the warm environment and rarely pools, leading to a hard time diagnosing the leak.
Click to expand...
Had water pump changed a couple of years ago. Also had thermostat and sensors changed last summer. No issues then.
 
As the coolant tank cap is cheap replace that with a good OEM quality one. The cap is the relief valve for the coolant and over the years the mechanism wears and fills with debris. It is possible now the cap is letting the fluid escape through the square over flow hole in the expansion tank. The rubber O ring also ages and the threads of the cap wear. Fortunately the cap wears more than the expansion tank but that may also need replacing.
 
The coolant housing below the tandem pump which also houses the coolant temp sensor can weap, new housing and coolant temp sensor seal is not a bad place to start
 
The car is in the garage today. Just had a call. The radiator bottom hose is split. They can't source a replacement. Any ideas for an after-market one, or does anyone have a decent one sitting around? Not sure of part number!
 
I don’t think I’ve got one there for a TDI. Only FSI.

I have a “potential breaker” coming in next week that’s a TDI.

I’m hoping Andy is going to be able to help as he’s just finished breaking a TDI.
 
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