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Q: My Jetta is overheating. Started slowly at first, but now overheats in 5km. on 1990 Volkswagen Jetta

I have replaced all temp pickups and fan switch, thermostat (drilled 3mm holes X2), have replaced the reservoir tank.
While thermostat cap was off, checked impeller, used torch and screwdriver to c if impeller is broken or loose (100%). NOT loosing water, no oil in water, no vapor out of exhaust.
Put a manual over-ride switch on fan, temp keeps climbing. Took head off, checked (NOT blown gasket or cracked). Took all hoses off and forward and backward flushed everything, yes, heater on full heat. Took radiator out and flushed as well and inspected (100%). The system gets presurised, can feel it on the hoses can c in reservoir as well the water squirting. Asked a mechanic for advise, he checked everything as well, and said, "Hey pal, you have one hell of a problem. All my ideas are done."
Please help, I've now spent what funds I had and still no solution.
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If it is overheating going down the highway, you most likely have a cracked head or possibly a plugged catalytic convertor. Seei if some shop in your area has a combustion leak tester. That should give you the answer. I have had cracked heads that won't show up cold and even sometimes on a hot engine until you put a load on the engine. I know you said you had it checked but was it by a professional or just visually looked at?
It was pressure tested before stripping the head. I have stayed away from the highway as I do not want to have a breakdown there. This model do not have a catalytic convertor.
Pressure testing won't detect a hairline crack in a cylinder head. I get two or three of these complaints in my shop every and have been in business for 25 yrs. You can purchase a combustion leak tester at local parts store for under $50. They are simple to use and should confirm your problem.
Ok, thank you very much. Looks like I will have to save up and get a cyl head, because everything else has checked out 100%.
Have a great day.
I have had customers who weren't convinced either until I performed that test. What is odd is, I have had no overheating in the shop running (even the fans cycle on when they should). Then you go drive it and "boom" the temp. starts rising.
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