I have an 1984 manual 1.9 petrol DG engine with NO THERMOSTAT and a serious overheating problem!
What I mean is that the thermostat housing is empty... save for a sealing ring and the remains of a thermostat, it looks like the main bit has been sawn off:
I have been trying to fix the overheating - firstly by bleeding the system.
Only now that bleeding hasn't worked I have resorted to looking at thermostat.
I followed various guides on how to bleed the system (both with and without raising the front of the van!) but my expansion tank doesn't hold pressure so perhaps this (and the missing thermostat?) has been thawting my attempts...?
Would a missing thermostat cause overHEATing or overCOOLing?
I think I am going to replace it anyway (and my expansion tank) then try bleeding again... Is it worth checking the water pump whilst I have the thermostat off? How would I do this? And why is there loads of sealant around where the thermostat housing joins onto the pump... do I need to clean it off and use fresh stuff when I reassemble?
The thermostat enables the coolant to circulate around the engine initially on warm up then it opens when warm and allows flow to the radiator to be included in the loop. Missing the stat out means that the engine will take longer to warm up increasing engine wear but it is not likely to be the cause of overheating. Not done a pump yet but common sense would suggest cleaning up of the mating surfaces before fitting the new one if its not pushing the coolant around the system could be one cause of your problem. Apparently it CAN be done with the engine in but access is poor.
There is a possibility that there is a blockage in the system somewhere sometimes rad weld is used which clogs up the system which is one , or rust blocking the radiator. Back flush the system to see if you can free it up
There are 5 ports on my thermostat housing. 2 which send water from the engine into the thermostat housing and 1 that returns it to the engine. There is also one that sends water to the radiator and another that returns it. I think these are the same as in the diagram.
As my thermostat is missing, all 5 ports are directly connected to each other via the void in the thermostat housing.
Surely this means water will NEVER flow through the radiator... If both its send & return pipes are directly connected to the same place (the void in the thermostat housing) then there is equal pressure on both ends of the radiator loop. No pressure difference equals no flow surely - Why should the water flow down one of them rather than the other?
Also... if the water entering the thermostat housing frm the engine can flow directly back into the engine why would it bother to take the scenic route thru the rad which would surely offer more resistance?
When the thermostat heats up, and becomes 'open' does it also shut off the flow of water from the engine back to itself? Maybe I am not getting something here... Surely this has to happen in order for water to go thru the rad?
Good point, I dont really understand it, but I think the pressure differential is created by the narrowness of the engine side pipes versus the wider bore of the rad side. A non return valve would be a way too, but I am not aware of one. When the stat opens it allows coolant into the top half of the chamber, it doesn't shut off the engine side. What I do know is that it works if all the bits are there as the VW engineers intended. Maybe someone with a better understanding of fluid dynamics can set you straight.
ok, thanks! I shall wait to see if anyone can elaborate, in the meantime I will probably just replace it anyway as its only a tenner and I am going to the shop for other parts away...
ambivert wrote:ok, thanks! I shall wait to see if anyone can elaborate, in the meantime I will probably just replace it anyway as its only a tenner and I am going to the shop for other parts away...
Non geniune thermostats are really poor quality at the moment, they are nearly all faulty from new.
If someone has butchered the thermostat, i would say it was from desperation to stop it over heating. Does the heater work, if it does waterpump is ok. The next thing i would do is check the rad. Does the rad get hot?
I experimented with thermostat removal about 20 years ago. It resulted in overheating. Overheating resulted in head shims leaking and further overheating.
The fact that someone had butchered the thermostat means that they have had some idea about what they were doing because the resistance of the remnant of the thermostat should have allowed the water to flow correctly.
Sadly, i have found that once an overheat has occurred, it usually ends up with head shims needing replacement.
There is a kit available on ebay, if you look under cylinder head tools that allows you to check for compression gases in the water system. 30 quid well spent.
The heater doesn't work, or if it does it doesn't work very well at all.
I think I once felt lukewarm heat coming out when I first got the van.
The rad NEVER gets hot.
So if this is a pump fault then, how do I test it?
Hope its not the head shims... sounds expensive... the engine was replaced only 3 years ago!!! although if the previous owner has melted it perhaps that doesn't count for much...
Thanks for all your advice so far people.
I have to get to the bottom of this one way or another!!!
ambivert wrote:The heater doesn't work, or if it does it doesn't work very well at all.
I think I once felt lukewarm heat coming out when I first got the van.
The rad NEVER gets hot.
So if this is a pump fault then, how do I test it?
Hope its not the head shims... sounds expensive... the engine was replaced only 3 years ago!!! although if the previous owner has melted it perhaps that doesn't count for much...
Thanks for all your advice so far people.
I have to get to the bottom of this one way or another!!!
I would remove pump and have a look at the impeler and see if its breaking up. If there is a problem with engine as Laurie suggested yoe need to find the cause before replacing things. Is the coolant rusty coloured?
ambivert wrote:The heater doesn't work, or if it does it doesn't work very well at all.
I think I once felt lukewarm heat coming out when I first got the van.
The rad NEVER gets hot.
So if this is a pump fault then, how do I test it?
Your cab heater and radiator aren't going to get very hot with no thermostat in the cooling system. As Bob said above, once the coolant gets hot enough (having been heated up by the engine) the thermostat opens to allow the flow of coolant to the radiator where it is cooled down and then returned to the engine, to continue the cycle of cooling it down. If there's no themostat in place, coolant can flow to the radiator and cab heater whilst it's still only lukewarm.
There's no point trying to bleed your cooling system if all the parts of the cooling system aren't present and in good working order. As also stated in previous posts, only use genuine VW thermostats.
Is it possible that the thermostat was removed / butchered in order to provide some sort of crude fix for another problem? So when the cooling system is operating at the correct temperature and pressure does something start to leak e.g. radiator or header tank perhaps?
Good luck.
Tony
Looking for: window apertures for side windows, at the back of the van
T25; 1985; RHD; 1.9DG petrol / LPG; white Autosleeper high-top; Looking rusty again!
As far as I know, like almost every other part of the cooling system, it doesn't work in what most people think of a normal way. What i mean is, in a normal water cooled engine all the thermostat does is open the return from the radiator back to the engine.
What the VW thermostat does is simultaneously open the return from the radiator and close the engine recirc line. If get one of these thermostats and stick it in boiling water you can see that there are 2 discs connected to the spindle that moves. One disc opens the return and one closes the recirc.
This means that without the thermostat the recirc line stays open and you get overheating. Normally if your thermostat fails you can remove it and that'll get you home. Not so with these engines. Another VW design classic.
One disc opens the return and one closes the recirc.
ah ha ! I've not clocked this. the thing I still dont get though is that when stat is closed both outlets in the top half are closed when open it allow coolant into the top chamber, What are the two discs you speak of? has any one got a stat and housiing picture?
