1988 Type 85 quattro – thermostat failure, broken in two places. Any ideas?
I’ve had a very odd failure that I’ve never encountered before, and I’m hoping someone might have an explanation.
We have an ’88 Type 85 MB quattro in for extensive work. One of the major problem areas was the cooling system, where virtually everything was worn out and the system was full of rusty sludge.
I removed both radiators and had two new ones made. I also replaced the water pump (Febi), the block-to-water-pump stub pipe (new genuine), and the water transfer pipe (new genuine from Tradition). All the sensors were replaced, and I restored both water housings and the rear angle pipe. I also checked and ultrasonically cleaned the heater valve.
I flushed the system using a compressed-air/water gun. The heater matrix was particularly stubborn to unblock, but I persisted until the water ran clear. The amount of rust staining left across the car park was something I’d never seen before!
I then reassembled everything, leaving the radiator circuit bypassed, with no thermostat or expansion tank fitted. I filled the engine and cooling system with a strong mixture of Bilt Hamber Deox-C and distilled water, then brought it up to temperature a couple of times a day for two weeks.
After that, I flushed everything again using the air/water gun and blew the system clear.
I fitted the new radiators and ran the VW genuine 052 525 A2 cleaning solution (nearly £200 for the kit) with distilled water for 20 minutes, with the cooling fan operating. I then flushed the system again, and an unbelievable amount of rust came out once more.
Next, I sealed the system and filled it with the neutralising chemical, ran it up to temperature again, then drained it and flushed it with air/water before blowing it through with air alone.
I vacuum-filled the system with distilled water, ran it up to temperature, drained it again and blew it clear once more.
Finally, I fitted a genuine Wahler 069 121 113 thermostat from TPS and vacuum-filled the system with a 40% G12 Evo and 60% Quantum mixing water mixture. I brought it up to temperature, and everything appeared perfect.
I drove the car for a few days, then noticed steam on the rear of the windscreen. The blower fan was also making a terrible noise, so I replaced it and checked the heater matrix from above. Everything looked fine.
A couple of days later, I went to retrieve the wheel-alignment paperwork from the passenger footwell and found it wet, with sticky red coolant on it.
I dropped the driver’s glovebox and could see coolant dripping from underneath the heater box. As the matrix is the same as the Golf Mk1 unit, I had a Nissens replacement in stock. I removed the pedal box (again!) and replaced the matrix.
I then ran the car up to temperature, drove it home on two consecutive evenings and gave it a good run. The heater output was excellent, and the engine reached operating temperature within a few miles and stayed there.
The customer subsequently collected the car to go on the Quattro tour. About an hour later, he called to say that the temperature was dropping and the heater was blowing cold.
I wasn’t prepared to let him continue driving it in that condition, so he returned, collected his GT instead, and went on the tour without his not a quattro, missing a propshaft and rear differential. EXTREMLY embarrassing for me.
I ordered another thermostat and O-ring and then spent the next three days worrying about what had gone wrong.
Yesterday, I removed the thermostat and, to my horror and disbelief, found that it had broken in two places and was stuck fully open.
I simply cannot work out why this has happened. The thermostat was a genuine VW from TPS Wahler part, and the system had been thoroughly cleaned and flushed before it was fitted.
I’ve fitted another thermostat and am testing the car again, but I’d really appreciate some input from anyone who has encountered anything similar.
I checked the thermostat housing by feel as best I could (I should have used my borescope) and couldn’t detect anything obvious. The stub pipe is below the machined surface and appeared clear, and the replacement thermostat sits in position without any apparent obstruction. As some will know, this area is very tight without a lot of dismantling.
Has anyone seen a thermostat physically break like this? Could something in the housing or stub pipe be putting mechanical stress on it, or is there another possible explanation?
At this point, I’m struggling to understand what could have caused it, particularly after all the work that went into cleaning and rebuilding the cooling system.
Any thoughts or suggestions would be greatly appreciated.
I’ve had a very odd failure that I’ve never encountered before, and I’m hoping someone might have an explanation.
We have an ’88 Type 85 MB quattro in for extensive work. One of the major problem areas was the cooling system, where virtually everything was worn out and the system was full of rusty sludge.
I removed both radiators and had two new ones made. I also replaced the water pump (Febi), the block-to-water-pump stub pipe (new genuine), and the water transfer pipe (new genuine from Tradition). All the sensors were replaced, and I restored both water housings and the rear angle pipe. I also checked and ultrasonically cleaned the heater valve.
I flushed the system using a compressed-air/water gun. The heater matrix was particularly stubborn to unblock, but I persisted until the water ran clear. The amount of rust staining left across the car park was something I’d never seen before!
I then reassembled everything, leaving the radiator circuit bypassed, with no thermostat or expansion tank fitted. I filled the engine and cooling system with a strong mixture of Bilt Hamber Deox-C and distilled water, then brought it up to temperature a couple of times a day for two weeks.
After that, I flushed everything again using the air/water gun and blew the system clear.
I fitted the new radiators and ran the VW genuine 052 525 A2 cleaning solution (nearly £200 for the kit) with distilled water for 20 minutes, with the cooling fan operating. I then flushed the system again, and an unbelievable amount of rust came out once more.
Next, I sealed the system and filled it with the neutralising chemical, ran it up to temperature again, then drained it and flushed it with air/water before blowing it through with air alone.
I vacuum-filled the system with distilled water, ran it up to temperature, drained it again and blew it clear once more.
Finally, I fitted a genuine Wahler 069 121 113 thermostat from TPS and vacuum-filled the system with a 40% G12 Evo and 60% Quantum mixing water mixture. I brought it up to temperature, and everything appeared perfect.
I drove the car for a few days, then noticed steam on the rear of the windscreen. The blower fan was also making a terrible noise, so I replaced it and checked the heater matrix from above. Everything looked fine.
A couple of days later, I went to retrieve the wheel-alignment paperwork from the passenger footwell and found it wet, with sticky red coolant on it.
I dropped the driver’s glovebox and could see coolant dripping from underneath the heater box. As the matrix is the same as the Golf Mk1 unit, I had a Nissens replacement in stock. I removed the pedal box (again!) and replaced the matrix.
I then ran the car up to temperature, drove it home on two consecutive evenings and gave it a good run. The heater output was excellent, and the engine reached operating temperature within a few miles and stayed there.
The customer subsequently collected the car to go on the Quattro tour. About an hour later, he called to say that the temperature was dropping and the heater was blowing cold.
I wasn’t prepared to let him continue driving it in that condition, so he returned, collected his GT instead, and went on the tour without his not a quattro, missing a propshaft and rear differential. EXTREMLY embarrassing for me.
I ordered another thermostat and O-ring and then spent the next three days worrying about what had gone wrong.
Yesterday, I removed the thermostat and, to my horror and disbelief, found that it had broken in two places and was stuck fully open.
I simply cannot work out why this has happened. The thermostat was a genuine VW from TPS Wahler part, and the system had been thoroughly cleaned and flushed before it was fitted.
I’ve fitted another thermostat and am testing the car again, but I’d really appreciate some input from anyone who has encountered anything similar.
I checked the thermostat housing by feel as best I could (I should have used my borescope) and couldn’t detect anything obvious. The stub pipe is below the machined surface and appeared clear, and the replacement thermostat sits in position without any apparent obstruction. As some will know, this area is very tight without a lot of dismantling.
Has anyone seen a thermostat physically break like this? Could something in the housing or stub pipe be putting mechanical stress on it, or is there another possible explanation?
At this point, I’m struggling to understand what could have caused it, particularly after all the work that went into cleaning and rebuilding the cooling system.
Any thoughts or suggestions would be greatly appreciated.
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