Thermostat Housing Plug

[jarrensc]

Hi all, as a fresh member to this forum I thought I would say a quick hello, then follow with dumping my problem/s into the hands of those with much more wisdom then me!

Brother just bought a 94 tdi 300 defender and we were getting some maybe phantom over heating problems when then dropped down under about 2k revs. So we decided that the first problem to address would be the coolant system.

After an entire day of screwing things up we had it all back together with a new radiator, hoses, thermostat all that jazz. Only problem was that the previous owner had chewed the thermostat housing plug up so bad that the socket/wrench just slipped off. https://www.aulro.com/afvb/images/imported/2014/10/1562.jpg

So we sorta ignored it and hoped it wouldnt matter for now. Once we had the fluids put in as best as possible we started it up and the temp from the start was on the off the scales hot. Ran it for about 5 minutes or more, the other hoses all started heating up. The top? hose wasn't hot at all so i'm guessing the thermostat hadn't opened yet? But at the point we chickened out and turned it off cause we are a bit scared of Diesels as we have never had one before (Runaway diesel???:eek: )

So heres my question if you did keep reading all of that. Do I just keep it running and hope the thermostat opens and the sender will start, you know sending and alls good in the world. Or do I need to get that buggered plug out?

[jboot51]

That is well and truly sad looking.
If you cant get it out then there is a small rubber hose connected to the left of the thermostat housing.
Disconnect the rubber hose and remove the plug from the top of the radiator.
At the other end of the small hose is a 3 way fitting.
Remove the fitting and ensure you can blow air through it in all directions and then refit.
This fitting helps remove air from the system.
Fill the header tank until fluid comes out of the top of the radiator then put the bung in.
Keep filling until fluid comes out where the small hose connects.
Put the small hose back on.


Massaging the bottom radiator hose while filling will help.

[Judo]

I recommend persevering with the top bung. It definitely sounds like an air lock.

It's one of those jobs that is incredibly tedious but really needs doing.

[jarrensc]

Did what you said jboot51 and the hose that went to the thermostat housing was clogged with some grey stuff

https://www.aulro.com/afvb/images/imported/2014/10/1487.jpg

Put in a temp house just to see if I could get it all working

https://www.aulro.com/afvb/images/imported/2014/10/1488.jpg

Started it up and same thing temp gauge went all the way to hot even when it was dead cold. The new hose did let the system air out a bit i was pumping the hoses and quite a bit came out. Stopped and started the car a few times till that new hose didnt fill up with air but still no change to the sender, still reading high and the thermostat didnt seem to open cause the top hose wasnt getting hot nor the radiator.

Whats the chance of it being a faulty thermostat ? And also the sender? With the wire that goes to the sender disconnected it reads cold on start. With the wire connected to the old sender but just the sender sitting on the block ( Not bolted in)

[jarrensc]

If that hose is moving the coolant fine then is there any point trying to get that brass plug out?

[Judo]

How long did it take for the temp gauge to go up to hot? If coolant is flowing correctly but the thermostat is closed you could idle it forever and not get the gauge to read hot. You need load on the engine to warm it up.

If it is shooting up to hot very quickly, then you either have a faulty sender/gauge or the coolant is not flowing correctly. Eg. Air lock still.

Could the heater core / pipework be blocked restricting flow? Eg. more grey stuff?

[jboot51]

with the engine running, even from dead cold, there should be coolant flowing through that new hose you put on, maybe pick the revs up a little and any air will make its way to the header tank.


The 3 way connector and the other 2 hoses need to be clean aswell


It takes a good 10 minutes at say 2000 rpm to open the thermostat on a 300 tdi.


Faulty sender would be my guess


You can take the thermostat out and have a look, no gaskets required as it has a rubber sealing ring.
Test it by putting it in boiling water.


You've got the clear expansion tank, on mine from cold, with a few revs, the coolant flows up from the little hose and hits the roof of the header tank.

[jboot51]

That grey stuff looks ugly-some sort of stop leak maybe???

[jarrensc]

How long did it take for the temp gauge to go up to hot?


The gauge hits its hottest point (Off the charts) the second you turn the key. Might put the old sender back in tomorrow run it for 10 minutes and see how we go.

[jarrensc]

with the engine running, even from dead cold, there should be coolant flowing through that new hose you put on, maybe pick the revs up a little and any air will make its way to the header tank.


The 3 way connector and the other 2 hoses need to be clean aswell


It takes a good 10 minutes at say 2000 rpm to open the thermostat on a 300 tdi.


Faulty sender would be my guess


You can take the thermostat out and have a look, no gaskets required as it has a rubber sealing ring.
Test it by putting it in boiling water.


You've got the clear expansion tank, on mine from cold, with a few revs, the coolant flows up from the little hose and hits the roof of the header tank.

Yeah I am probably now getting about that much coolant movement in the header tank. Think i will let it run a bit longer than I have, see if I can get a change.

Been comparing the heat up time to a nissan pathfinder which in about 5 minutes it would of started opening and showing up on the temp gauge.

Will definitely be testing the thermostat and hopefully with the old sender back in I will see some results.

Fingers crossed for tomorrow.

[Judo]

The gauge hits its hottest point (Off the charts) the second you turn the key. Might put the old sender back in tomorrow run it for 10 minutes and see how we go.

Ok, well that sounds like a sender fault. Possibly a short across the sender...

[jarrensc]

Just pulled out the Thermostat. Put the pan on the stove and threw in the old and new thermostat. Old opened a lot faster and about doubt if not triple the gap of the new one... So is that a good thing? Does it mean the new one is a dud or is it just a bit slower cause its newer?

[jboot51]

Good question.
I had the same thing and went with the old.

[jboot51]

Are the heater hoses for the cabin are still connected/haven't been messed with ????

[jarrensc]

So far so good. Just ran it for about 15 minutes and it looks like the old thermostat has opened. With the old sender in the temp gauge moved into the normal running temp and everything looking golden.

Going to take it for a test run once its cooled down a bit so i can see if i need to top up the header tank.

Moral of the story? Don't use new parts? Haha No idea. Going to need to keep looking into the thermostat thingo though cause the old one isn't looking that hot fresh.

Thanks so much for everyones help! Really needed it. If you still have some knowledge to enlighten me with in regards to that termostat thing then please continue laying it down! :D

[jarrensc]

Are the heater hoses for the cabin are still connected/haven't been messed with ????

Have no idea. Not even sure how the heater works as of yet, since from buying it the heater controls seem to do nothing. Fan doesn't come on or anything. Now that the car is running at normal temps i can see if the AC is working

[jboot51]

Re-heater hoses
If you do have to disconnect the heater for some reason, the 2 heater hoses must be looped together to maintain a flow circuit or the head will overheat.

[AndyG]

With the grey gunk there i would be doing a full flush ASAP