1.9DG overheating.

[Tommy D]

I have fluid for my head gasket tester on order so that will of course get checked this week!

The bus has been stood for 6 years and the coolant system was bone dry when i picked it up.

i have filled the system up and bled it all out (rad and thermostat bleed points) and it was perfect for 2/3 days...

one day the heaters stopped blowing warm.
next trip the temp gauge went to max and stayed there briefly (fan on a switch, so turned this on and it made no difference)
then went back down again and back up again.

with the heaters being cold, i first assumed a faulty sender or gauge...
but also thought it could be an air lock but before i could check for airlocks it threw its coolant from the thermo housing.

so i fill her back up and re seal, re bleed and go for a run... bled the system, rad warms up, all air gone (as per the brickwerks system bleed advice)

to no avail... she she keeps overheating now without the gauge going back down.

temp unaffected by the rad fan but the rad KEEPS going cold.

next step and the head gasket test is the flush the system with my pressure washer...

any advise is appreciated... cheers

[ermie571]

The pump is running, yes??

[Tommy D]

i assume so because when i rev with the header tank cap off the level goes up and down

[itchyfeet]

You don't say what year your van is cooling systems change early to late but with both the cab heater is a seperate circuit to the radiator circuit
so heat in the cab is no indication the thermostat and rad are working.

when you bled the system did you check the rad got hot top to bottom and the thermostat opened, this is indicated by the pipe to the thermostat getting too hot to touch, ideally you wait for rad fan to cut in but that may never happen in winter ( not clear to me from your post if rad fan is cutting in)
If there was still air in the rad circuit because thermostat didn't open then when it did finally open the air circulates causing your symptoms.

Don't use a jet washer, the pressure is too high, a hose pipe and a rag to get a bit of a seal is enough.

[itchyfeet]

One more thing have you removed and checked thermostat opens in a pan of water on the stove?
if it's partially siesed then flow will be reduced causing the engine to overheat.

[CovKid]

Sounds like you still have air in there. From experience (and the big swings in temperature you describe would seem to fit) it still hasn't been bled properly. When you rev it, it should be enough to really annoy the neighbours. I had to run it at well over 2000 revs (more like 2,500-3000 revs) to fully expel the air and it still took three goes to do it.

With a system that has been dry, the likelihood of hidden air pockets is substantially greater. Air in the system will cause it to overheat for sure. Its very frustrating (got the T-shirt) but I think you'll need to bleed some more and probably rev higher than you think. You need to push that water through and the air with it.

If its any consolation, I too thought there was something seriously amiss but it was wholly down to not giving it enough revs to fully expel the air. With a system that has been stood that long and gone dry, I'd only use water first so I was sure it was fully bled and also watertight, then when I was happy, drain a good 8-9 litres away and add the antifreeze and a final bleed. Water is cheap.

[Tommy D]

notes to add....

thermostat has been removed.
86 c reg van, late system.

im gonna pull the rad off on sunday and flush it and the pipes incase of any blockages.

[itchyfeet]

thermostat has been removed.
.

?..and replaced without testing
?...and tested then replaced
?...left out altogether

[Tommy D]

thermostat has been removed.
.

?..and replaced without testing
?...and tested then replaced
?...left out altogether

removed altogether. was seized due to being stood so just removed it and never fitted another.

[Tommy D]

When bleeding the rad, it was getting completely warm whilst bleeding but one the van started overheating the rad had gone cold, thus the fan not being switched on isnt effecting the cooling process.

i cant understand how the rad will warm up and be bled happily but then go cold and the motor overheats.

fan it rigged to a switch on the dash due to a faulty sensor in the rad not kicking it in.

[CJH]

This sounds like an air lock - maybe pockets of air that didn't cause a lock by themselves initially, but once they accumulated they did cause an airlock and your radiator went cold. A good vigorous bleed as per Covkid's instructions would clear that.

But it could also be a blockage somewhere. Do you know how long it had stood with no coolant in, or what the history was like before that? I bought a scrap engine for refurbishing. It had been stood in a scrapyard for a long time, so was bone dry inside. When I removed the old water pump it was completely clogged with dry rusty deposits, presumably from being run for a long time without the correct coolant.

If yours had something similar inside you could have dislodged it and clogged something somewhere. A good flush would then be needed.

I'd start by bleeding it thoroughly though.

[Tommy D]

This sounds like an air lock - maybe pockets of air that didn't cause a lock by themselves initially, but once they accumulated they did cause an airlock and your radiator went cold. A good vigorous bleed as per Covkid's instructions would clear that.

But it could also be a blockage somewhere. Do you know how long it had stood with no coolant in, or what the history was like before that? I bought a scrap engine for refurbishing. It had been stood in a scrapyard for a long time, so was bone dry inside. When I removed the old water pump it was completely clogged with dry rusty deposits, presumably from being run for a long time without the correct coolant.

If yours had something similar inside you could have dislodged it and clogged something somewhere. A good flush would then be needed.

I'd start by bleeding it thoroughly though.

i have bled... or tried to bleed it a good few times now. rads coming off next and im flushing it front the back and starting again.

[CovKid]

Don't think you need to do that. Remember it needs to warm up and revved high enough. Two man job in this instance I think. I put a brick on the throttle but I was still running front to back, topping up, checking temp and opening bleed screw. Still say its an airlock. I had all of that until the air was pushed out. Squeezing hoses seemed to help a bit when I did it. Also standing for a while after every bleed sometimes encourages the air to bubble up. If it gets too hot during bleeding you have to let it cool down then start again.

[CJH]

One technique I've found helpful while the engine's still cold is to use the pump to pressurise the system so you can get more water in. This seems to force air around and out more quickly.

So:
- remove the dalek cap from header tank, top it up to the brim.
- use right hand to operate the throttle. With increased revs the water pump pressurises the system a bit and the header tank level will drop (I guess the rubber hoses are all expanding a bit, but also any air in the system will compress a bit).
- while keeping the revs high, top up the header tank with your left hand, and put the dalek cap back on tight.
- release the throttle.
- let it run for a few moments then repeat.

Obviously, take GREAT care removing the dalek cap once everything starts to warm up, since the coolant will be hot, and once the system starts to pressurise normally through increased temperature that hot coolant will spurt out. In fact, don't remove it all once everything starts warming up.

[itchyfeet]

The thermostat has two states open and closed

But there are two circuits, a bypass the rad circuit and a full circuit.

The thermostst when closed opens the bypass circuit, the thermostat when open diverts the bypass circuit ( early systems it closes it)

Taking the thermostat out means the coolant does not flow as Mr. VW intended so it won't bleed properly ( coolant takes a short cut and does not all flow via the rad)

Buy a new thermostat ( preferably a good quality one from Brickwerks) fit it and then bleed the system

When you look at this diagram you can see when the thermostat changes state the coolant in the bypass hose changes direction from the arrow on the diagram