P38 Coolant - confused.com...!

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New (pink) coolant seems fine but I am not sure the radiator is fully cleared of air. The reservoir holds pressure OK, but when I remove the cap after a day or two, residual pressure is still there but it makes the most alarming gurgling and spills a bit of coolant.
As the cap side seals on the barrel look worn, I got a new cap - see photo.
Not sure whether to go though the bleeding process or just fit the new cap and let it sort itself out.
As I understand it, the bleeding process is:
Remove the reservoir cap and bleed pipe from the top of the radiator and blow through the pipe.
Replace the pipe but leave the cap off.
Run the engine at idle until the top hose is warm, taking care to keep the reservoir level at the "cold level" mark.
Then stop the engine and leave to cool.
When cool, refit the cap.
Is that correct?
Comments appreciated, as ever.

Rad caps old and new.jpg
 
P38 Monkey said:
New (pink) coolant seems fine but I am not sure the radiator is fully cleared of air. The reservoir holds pressure OK, but when I remove the cap after a day or two, residual pressure is still there but it makes the most alarming gurgling and spills a bit of coolant.
As the cap side seals on the barrel look worn, I got a new cap - see photo.
Not sure whether to go though the bleeding process or just fit the new cap and let it sort itself out.
As I understand it, the bleeding process is:
Remove the reservoir cap and bleed pipe from the top of the radiator and blow through the pipe.
Replace the pipe but leave the cap off.
Run the engine at idle until the top hose is warm, taking care to keep the reservoir level at the "cold level" mark.
Then stop the engine and leave to cool.
When cool, refit the cap.
Is that correct?
Comments appreciated, as ever.

View attachment 292893
Click to expand...

Personally I rev it to 2,500 rpm with the car parked uphill. Give the hoses a good squeeze pumping every so often too.

Have you tried pressure testing each cylinder?
 
Car parked uphill surely means that the radiator is higher and therefore less likely to transfer any air from it into the reservoir?
I know there is air in the radiator, as when I take the bleed pipe off, no coolant runs out.
What is the reason for pressure-testing the engine?
Engine runs fine by the way, and the temp gauge is absolutely central regardless of speed / load / town running / zircon load etc.
 
Is this the v8?
Take the radiator cap off, undo the bleed pipe and blow down it until it's clear. Reattach to the radiator, leave the cap off and start the car
Run at 2000 rpm for the pump to get some gusto for a minute, that should help get the air out.
 
If you can, jack up the right front corner, helps the air to get to the bleed corner of the radiator. Pointing uphill but across a slope is helpful too. Sometimes running it with the cap off and blocking / releasing the bleed hose hole in the reservoir neck helps it to get flowing through. Burping the top hose also helps to get air through and bled.
Make sure all the clips everywhere are tight, or it may bleed air but also draw it in at another point.
 
Scotiawhiskers said:
If you can, jack up the right front corner, helps the air to get to the bleed corner of the radiator. Pointing uphill but across a slope is helpful too. Sometimes running it with the cap off and blocking / releasing the bleed hose hole in the reservoir neck helps it to get flowing through. Burping the top hose also helps to get air through and bled.
Make sure all the clips everywhere are tight, or it may bleed air but also draw it in at another point.
Click to expand...
Good advice - thank you. I believe the problem is air leaking back into the radiator due to bad seal at the o-rings on the radiator cap body. New cap fitted and will report results... Thanks again.
 
P38 Monkey said:
Car parked uphill surely means that the radiator is higher and therefore less likely to transfer any air from it into the reservoir?
I know there is air in the radiator, as when I take the bleed pipe off, no coolant runs out.
What is the reason for pressure-testing the engine?
Engine runs fine by the way, and the temp gauge is absolutely central regardless of speed / load / town running / zircon load etc.
Click to expand...

I had some coolant issues so I made an adapter from an old conpression guage to fit the glow-plug hole (spark-plug on v8) and used my airline to pressurise each cylinder in turn, checking the valves were shut by looking at the cam. That's how I discovered my engine was leaking into the coolant as all of a sudden the expansion tank emptied itself on one of the cylinders. If it is caught early there might only be a tiny leak.

More likely something like the heater matrix leaking to be fair or it could just be trapped air, especially if it is an aftermarket stat but something to consider.
 
Datatek said:
The P38 temperature gauge stays just to the left of 12 o'clock from about 80C to 105C.
Click to expand...
What, do they all do that?? Lulling us into a false sense of security??
How do you know the actual temperatures as you quote above - some attached remote thermometer?
Would be a good idea to fit one I think.
My gauge needle is at 12-o'clock all the time, like Andrew Tate on a good scenting day.
 
Grrrrrr said:
I had some coolant issues so I made an adapter from an old conpression guage to fit the glow-plug hole (spark-plug on v8) and used my airline to pressurise each cylinder in turn, checking the valves were shut by looking at the cam. That's how I discovered my engine was leaking into the coolant as all of a sudden the expansion tank emptied itself on one of the cylinders. If it is caught early there might only be a tiny leak.

More likely something like the heater matrix leaking to be fair or it could just be trapped air, especially if it is an aftermarket stat but something to consider.
Click to expand...
Oh boy, another problem I didn't know I might have...
P38 running perfectly, but what problems are lurking hidden under the bonnet..??!?
 
P38 Monkey said:
What, do they all do that?? Lulling us into a false sense of security??
Click to expand...
Exactly that. An idiot gauge!
P38 Monkey said:
How do you know the actual temperatures as you quote above - some attached remote thermometer?
Would be a good idea to fit one I think.
Click to expand...
I can confirm the 'about 80c' it's not exact or consistent so must be some fuzzy logic in there
I've read 105 in RAVE i think, ac fans come on at 108 if i recall. But that's way too hot for the v8
You can get the actual temp with the Android torque app and a Bluetooth obd adapter
 
P38 Monkey said:
What, do they all do that?? Lulling us into a false sense of security??
How do you know the actual temperatures as you quote above - some attached remote thermometer?
Would be a good idea to fit one I think.
My gauge needle is at 12-o'clock all the time, like Andrew Tate on a good scenting day.
Click to expand...
I have taken a lot of temperature readings for the purpose of setting the FIP modulation using diagnostics.
 
kermit_rr said:
Exactly that. An idiot gauge!

I can confirm the 'about 80c' it's not exact or consistent so must be some fuzzy logic in there
I've read 105 in RAVE i think, ac fans come on at 108 if i recall. But that's way too hot for the v8
You can get the actual temp with the Android torque app and a Bluetooth obd adapter
Click to expand...
Not on the diesel.
 
kermit_rr said:
Exactly that. An idiot gauge!

I can confirm the 'about 80c' it's not exact or consistent so must be some fuzzy logic in there
I've read 105 in RAVE i think, ac fans come on at 108 if i recall. But that's way too hot for the v8
You can get the actual temp with the Android torque app and a Bluetooth obd adapter
Click to expand...
Hmmm, time to get a remote thermometer methinks.
On my 1997 4.0SE, the radiator cooling fan has a viscous coupling which I assume is standard, and presumably not temperature-dependent.
The manual says that the a/c condenser fans are refrigerant pressure (not temperature) triggered, running in series (slow) or parallel (fast) as called for by the single and dual pressure switches.
But I would really like to know the actual engine coolant temperature...
 
P38 Monkey said:
Hmmm, time to get a remote thermometer methinks.
On my 1997 4.0SE, the radiator cooling fan has a viscous coupling which I assume is standard, and presumably not temperature-dependent.
The manual says that the a/c condenser fans are refrigerant pressure (not temperature) triggered, running in series (slow) or parallel (fast) as called for by the single and dual pressure switches.
But I would really like to know the actual engine coolant temperature...
Click to expand...
The fan viscous coupling is temperature dependent. Overheating is often caused by failure of the viscous coupling.
The aircon fans are indeed pressure operated.
If the gauge moves past 12 o'clock the temperature of the coolant will be in excess of 105C. On the V8, the aircon fans also come on if the coolant reaches about 110C, which is a bit on the late side IMO.
 
In my opinion the viscous can fail over time.. it will still do is thing but the temp will increase in unnoticeable amounts. Also, the set point on each unit isn't exact, so 2 perfectly good units can run your engine at different temps, which is generally fine, but the v8 stat isn't fully open until 96, which (again my opinion) is too hot for these engines, 90-92 would be better. Not a huge difference but i think the engine would love you for it and stop lots of problems
 
kermit_rr said:
In my opinion the viscous can fail over time.. it will still do is thing but the temp will increase in unnoticeable amounts. Also, the set point on each unit isn't exact, so 2 perfectly good units can run your engine at different temps, which is generally fine, but the v8 stat isn't fully open until 96, which (again my opinion) is too hot for these engines, 90-92 would be better. Not a huge difference but i think the engine would love you for it and stop lots of problems
Click to expand...
A tropical thermostat would be good, coupled with an electric fan.
I imagine there are electrical fan kits for these (4.0SE) engines?
And maybe hot-climate thermostats?

We recently fitted a tropical thermostat to my son's 1990 VW Golf GTi: it opens a little earlier, but more interestingly it opens wider and faster than a standard one. The Germans are competent in hot climates, well they were until they met Monty.
 
Question: if the a/c condenser fans are on, presumably they are blowing through the radiator as well as the condenser. Ergo having those two fans on also helps cool the engine?
Even if the main fan viscous coupling is weak.
So leaving the a/c on is good for the engine???
I like that argument!
 
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