Hi.
I got another problem with my 4x4 Saph.
I've just rebuilt the engine.
During driving with normal speed everything seems to be right. The temp. gauge shows "O" (maybe a little to high, but sometimes between O and R), temperature outside is about 27 - 28°C.
When I get back home and turn off the engine, the coolant in header tank starts to "boil" after about 1 minute. (I see bubbles coming out from the turbo return hose).
As you see, the coolant level raises just to the cap. All the "boiling" takes about 2-3 minutes and when it cools down, the water level returns to the normal (max mark).
Radiator fans are working okay. I cooked a thermostat in a pot and it's good (opens just before the water starts to boil). I replaced the tank cap. I made two "CO₂" tests on hot engine (one of them for over 4 minutes). The reactive fluid does not change the color, so I think maybe there are no exhaust gases in the coolant. There's no coolant in oil and no oil in coolant. I did not touch the "bleed screw" on the thermostat housing.
Can you tell me what may be the reason for such water boiling? (I got another cossie and it doesn't boil the water so intense after turning off the engine).
What else should I check?
Thank you for your help!

 

Hi mate. You say the thermostat opens just before boiling. Should open at either 82 or 88 degrees depending on which one you have IIRC. That could be the problem.
Once I have done a coolant change I Ieave the header tank cap off on mine until a couple of fan cycles and a good squeeze of the hose you have squeezed in your video.

 

Sorry, I wrote it a bit wrong. During cooking, the thermostat opens smoothly and I did not even boil water until it was completely opened. I remember I changed it for a new about one year ago. There is only "Made in England" written on it and a "82" or "88" stamp (I do not remember).
Could you tell me how to use the "bleed screw"? When the engine is hot or cold? When engine is running or turned off?
Thanks.

 

Ahh, no worries.
I would use the bleed bolt when you think the thermostat is open whilst it is running. Don't undo it all the way, just enough for a good amount of flow for a few seconds should be enough. Bit messy lol but...........
I also usually leave my header tank cap off aswell until 2 fan cycles have completed whilst also squezzeing that hose.
Also of note, is your heater control on max??

 

thanks for reply. I'll do as you say and report about results in the evening
The interior heater is off and temp. gauge is on the "O", when I turn the heater on and switch it to the third lever, the temp gauge drops between "O" and "R"
I'll also check if both radiator hoses are cold or hot.

 

Does it only boil when the engine is stopped? I think it might just be the water boiling in the turbo when the water pump isn’t running anymore. I noticed this on mine as well a while back, but there was nothing wrong and it’s still going strong.

 

Yes, only when I turn off the engine and it's starts about after two minutes and takes another 2-3 minutes.

I did as kosienutter said. Started engine with header tank cap opened, waited for the fans to turn on twice. Then I turned off the engine, I loosened the bleed screw. Everything was okay. So I took the car for a ride and after returning the same. Boiling again. Then I disconnected the turbo cooling and made a bypass. The temp gauge shows the same like before. After the next ride, basically calm. Only a few bubbles appeared in the header tank, but the strange thing is that the lower radiator hose was just cold and upper main hose was really hot. Tomorrow I will connect the turbo cooling back, try to remove the thermostat and drive the car again. And then? I don't know. The water pump? Radiator?

 

Had a normal Sierra back in the day that came in the garage after having water pump , head gasket, radiator you name it. Everything replaced.

All that was wrong with it was the return to the header tank was blocked up. Ran a drill bit through the return on the header tank coolant circulated better and no more overheating..

Worth a check!

 

The upper radiator hose is supposed to be hot as it is the supply. The bottom hose is the return, so depending on how good the radiator is doing its job it should be colder.

But what are you actually trying to solve? Because to me it doesn’t seem there is actually anything wrong.

 

Id go back to basics.....drain the system...run a hose through to check the circulation...

Then if thats ok fill it back up, run it up with the cap off...keep topping up untill level reached...heater in the car on hot..a couple of fan cycles

Rad cap back on....if that still returns a problem theres possibly something expanding/contracting when a high temp/cooling down???

Could be air trapped and once you turn off its forcing its way back to the top.

 

You're right, but the lower hose was really cold, as if the car did not even drive; as if the water in the radiator did not flow


well, I am afraid that something is blocking the flow of coolant or that I have connected something wrong. Maybe really air trapped?
It seemed to me that boiling so intensively in the header tank is not normal.
I have driven my other cossie (2wd) and there is no such issue. I can even open the tank cap and there is no pressure.

Thank you all for your advice. I will try to find the cause and write if I solve the problem.

 

This is a baffling one then
Like you say you have no trouble with your 2wd but then the system is as you know is different.
Just to check though. Are you still on standard hoses and also have you trialed it with out the thermostat in the housing??
One other thing is check for splits, this may draw in air maybe??? Sorry if I am waffling on a bit with all these ideas

Put a picture off your engine bay on here if your not sure if you have connected something up wrong??

 

Tommorow I'll put a pic of an engine bay. I did not have time to try the car without a thermostat today but I'll do it tommorow and report what happened.
I have old original hoses fitted, but I just ordered a Rouse motorsport kit for 4wd late models.
I drew a simple diagram of how I connected the coolant hoses.

 

so I'm after a ride without a thermostat. Outside temp. + 26°C
Everything seems fine. Both hoses of the radiator have a similar temperature. The car was warming up a few minutes longer. The temp. gauge shows "R" (sometimes between "O" and "R" when I stopped at traffic lights). The fans only turned on when entering the garage. After stopping, there was no boiling, no bubbles. After a while, I could open the header tank cap and everything was ok. I looked again at the thermostat and it has scratches in one place. Maybe it just blocked itself sometimes.

Last question I have:
What is the approximate difference in the temp. gauge display in terms of degrees Celsius between the letters N - O - R and M? Does anyone know?

 

Dont drive it without a thermostat as the water won’t flow round the engine correctly. The most common problem with the 4wd is the stat not opening correct causing overheating.
Put a new ford only stat in it do not buy a copy one from anywhere as they will cause a problem also.
Forget what the gauge says as they are rubbish. Get a proper gauge like a two wire stack and fit in place of the stock sensor if you want to see a real temperature reading.

Mark

 

Sweet. Seems as though it could be the thermostat. Time for a new one me thinks 😂😂

 

thank you all for your help

 

No problem