TD thermostat will not open HELP!!! Overheating engine

Post by **devoncamperman** » 04 Sep 2008, 20:01

Hi i have a 1983 T25 about 4 months ago i converted from Aircooled to water cooled using a 1.6 td from a Jetta and JX parts.

Ever since it runs great but if the thermostat is fitted, it will never open and the lower rad hose is always cold as there is no water flow back to the engine. I have been running with out a thermostat since and water flows through the rad and everything gets hot as it should but never over heats.
I even tried drilling a 2mm hole in the flange of the stat in case of an airlock, bled the system and rad as recomended, but the engine is overheating badly and i am to scared to run it. I have tried 2 thermostats 1 VW and 1 replacement both work exactly the same in a pan of water and open but will not open when fitted to the van.

The reason i want to fix this problem is that my heater matrix burst and this may have been a normal failure but i wonder if it may be connected (stat was out), so i want to get the van working with a stat before replacing the matrix which is a horrid job.
So please if anyone has any ideas why it won't open and can help i would appriciate it.

Post by **mahatmacoat** » 05 Sep 2008, 08:10

If you are certain that you have connected all your hoses the right way around - I'd double check this against another van if you're not certain. I'd look at the the water pump. Is your alternator belt (drives the water pump as well) in good state & tight enough? Then maybe the impeller, what state is that in?

How old is the thermostat & have you checked that it opens (Haynes trick of hanging it on a thread & then bringing a pan of water to the boil works well, or just chuck a new one in, they're not expensive.

What state is the coolant in, any signs of corrosion or silt in it? Have you tried a coolant flush additive (chuck it in, run it for 100miles & you'll be amazed at the crap that comes out).

Post by **ringo** » 05 Sep 2008, 12:23

I was guilty of this too - aparently you shouldnt run without the thermostat in as it ruins the flow (if you take the water pump off you will see what i mean) - instead, run a thermostat that has been drilled out.

When running a drilled out thermostat, does the radiator get hot?

If not, as suggested it could be the water pump is knackered.

Ringo

Post by **Ye Olde Syncrospares** » 05 Sep 2008, 14:39

impelor fallen off back of waterpump,cj.

Post by **devoncamperman** » 05 Sep 2008, 14:51

Thanks for the replies, i am sure the hoses are all correct, the water looks quite clean but i will get some flush and clean it out.
I don't quite understand, if the water pump was duff then how does it work so well with no thermostat, all pipes flow and return are nice and hot. With the cap of the header tank and i rev the engine you can see the water pump pulling down the level in the header tank so i assume it is working. Also when i undo the bleed vent on the rad and get some one to rev it water blasts out at high revs. If any one can explain on this, then yes please.
I have drilled 2x 2mm holes in the stat to try and stop air locks, do you think this is big enough.
P.s i have 2 stats 1 old 1 new.
Thanks i really need to get this sorted!!