thermostat on my scooby t25 will not open.

Sydney · Padawan Joined: 22 Sep 2012 Posts: 55

I'm thinking that either the bypass is not bypassing correctly, or the bypass pipe diameter is too small or the pipe lengths are too long or perhaps too exposed.
If you haven't used the van in such cold temperatures before, you may now be discovering that the water entering the sensing side of the thermostat is no longer hot enough to trigger it to open. If you're using your interior heater, it will reduce the temperature of the fluid entering the sensing side of the thermostat.
Are your pipes through the bypass valve lagged? If not they will also keep the thermostat sensing temperature down?
Are you always driving it when it overheats? If so try running it on your drive and see if it still overheats.

Bundy · Padawan Joined: 03 Sep 2010 Posts: 54 Location: Cheshire

just a thought following on from some suggestions...
On my conversion, EJ20 in an Earlybay, I had the by-pass pipe quite far down the van towards the front....the engine would semi-overheat before the thermostat would open. Sometimes a heafty blip of the throttle would sort it, but once I moved the by-pass much nearer the engine the problem has gone. I think that too much heat is lost down the length of pipes causing the thermostat to open too slowly.
Never know, might help!
Cheers
Al

Kai · Posted: Wed Dec 12, 2012 7:37 am Post subject:

This is all good information worth noting and would beleice that your provlem lies within your coolant circuit design.

With my conversion the only time it's over heated is since I've installed a heater into the coolant circuit. Usually caused by airlocks within the system. It's easy to see when mines going to overheat as the top hose entering my header tank (Vauxhall frontera type) should usually constantly pump fluid, when there air lock is playing up the coolant is inconsistent or not flowing which will cause the temperature to rise. Now the air is out its sits at the centre of the gauge.

My bypass consists of a plumbing stop valve which I close to force the fluid through the heater bleeding the air out of the system ( I also have a air bleed circuit for my system)
_________________
Think......

Don't sleep and drive!!!

jonathan · Padawan Joined: 09 Dec 2012 Posts: 51

Cheers guys for all the help,
im going to take my heater metrix off and pipe stright to the thermostat to see if i can get it to open,then i no thats the problem,bypass is right by the engine.pipes are not lagged but will try that aswell. It still over heats when i dont have the heaters on,
Iv just been driving round the streets to test it as dont want to be to far away when it over heats,
Im about to start on all these ideas and will let you no how i can on,
once again thanks everyone

jonathan · Padawan Joined: 09 Dec 2012 Posts: 51

Right had a break through, put a pipe straight from the bottom of my header tank,mist out all the heating matrix and went to the pipe that goes to the thermostat, so pipes only about 8 inchs long.Water is now flowing through pipes to rad,and rad is nice and hot,
But its still over heating when im driving around the streets, as soon as i put my foot down abit and get the speed and revs up it starts to cool down
Does this sound like the pump is broken and not circulating the water enough,

Kai · Posted: Wed Dec 12, 2012 11:37 am Post subject:

jonathan · Padawan Joined: 09 Dec 2012 Posts: 51

fans dont kick in as i disconnected them when i put the new rad in The gauge is the original one on the dash,wired up to rjes wiring loom.
Yep got a reversed manifold from rjes
the rad doesnt get really hot,just normal warm temp,and all pipes are warm which is a improvement as it wouldnt circulate with the heater matrix in, so the thermostat must be opening now but still overheating, the temp comes down the faster i seem to go,

Joel · Posted: Sat Dec 15, 2012 11:20 pm Post subject:

jonathan · Padawan Joined: 09 Dec 2012 Posts: 51

I hope its not the headgaskets as they were just changed when i did the conversion 10 months ago,
Its getting a new pump fitted on tuesday,
I really dont want to do the heads again.

jonathan · Padawan Joined: 09 Dec 2012 Posts: 51

had the heads done 10 months ago, has had new rad a month ago has had four different thermostats fitted just had a new pump in today and still will not open the thermostat

jonathan · Padawan Joined: 09 Dec 2012 Posts: 51

has any body heard of having to much anti freeze in the system which leads to changing boiling points and there for making engines over heat, a friend of mine had a ford rs turbo and he had all the problems iv had then a garage told him to try and just put water in and see if it worked,and sure enough the car stopped overheated. could this be true and the answer to my problem.

Sydney · Padawan Joined: 22 Sep 2012 Posts: 55

I think antifreeze increases the boiling point of the coolant but the opening temperature of the thermostat will remain the same and the temperature gauge will still be telling you how hot it is. I wouldn't recommend running without antifreeze this time of year. One cold snap and head gaskets will be the least of your problems.
I imagine you are bound to get overheating problems when driving slowly round town with the fans disconnected. Have you tried running without the thermostat?
I know it's not good for the engine if you do it for too long but it will allow you to get around for now, and it may confirm if the thermostat is the problem or if you've got a blockage somewhere else.
You can also buy lower temperature thermostats.