Question - not for the feint-hearted

YR2000 4.0Ltr petrol V8 - P38

Refer to section 8, page 8 of RAVE (or page 466 of pdf RAVE)

Q1. What causes the thermostat to open ?

A1. Thermostat opens when the temperature of coolant of either the coolant coming from the by-pass hose (from the top hose) or/and the coolant coming back from the heater matrix is sufficient to heat the wax element of the thermostat to make it open.

Q2. What keeps the thermostat open once engine has warmed up?

A2. When the thermostat opens it shuts off the coolant supply from the by-pass hose and relies on the temperature of the coolant coming back from the heater matrix to open/close dependent upon temperature.

Q3. If the radiator is warm all over does this mean thermostat has opened

A3. Yes, as it indicates that hot water from the top hose is flowing through radiator and thermostat.

Q4. Why the **** is it that i warm the car up with no viscous fan fitted, feel the radiator and it is hot all over meaning that the thermostat has open, but when i put the viscous fan on and take out for a run she overheats - when i feel the radiator is cold all over except the top ?

A3.............................................................................................


Before trying to answer Q4, read below:

New thermostat
New Fan
New pump
When ran with no thermostat - no overheating at all - radiator getr hot allover (it would...derrrrrrr)
New expansion tank cap
New top hose
New by-pass hose
New coolant feed hose
No pipe blocked
No pressure loss
Massive amount of time spent on getting rid of air lock - various methods tried - RAVE,Landyzone,internet,youtube and other LR forums

I am at the end of my thinking (tether) and at the point of giving up - tax due this month - do i run without thermostat ( severely tempted) or keep her off road for the winter.

Anyone got an answer to Q4?

Just as an experiment, you could try using the aircon fans for cooling and leave the viscous fan off. I can give you a mod to use the aircon fans.

Is the fan cowling all there present and correct? If you have no cowling it will make it overheat.
The other thing to remember that left static as the rad heats the heat will spread through the rad by conduction, the fan effect will reduce that.

Wiganerdan said:

Is the fan cowling all there present and correct? If you have no cowling it will make it overheat.
The other thing to remember that left static as the rad heats the heat will spread through the rad by conduction, the fan effect will reduce that.

Click to expand...

Leaving the cowl off should not cause it to overheat, it does increase fan efficiency but it is as much a safety feature as anything. The diesel will run happily without fan or cowl unless in slow traffic.

How do you run without a stat on the 4.0 and 4.6?? it is built into a plastic housing plumped into the coolant system near the bottom of the radiator....is the housing able to be split apart and stat removed as I thought they were moulded in!!

Saint.V8 said:

How do you run without a stat on the 4.0 and 4.6?? it is built into a plastic housing plumped into the coolant system near the bottom of the radiator....is the housing able to be split apart and stat removed as I thought they were moulded in!!

Click to expand...

You just mangle it

If you remove the stat from the housing it will overheat as it's a bypass system. A bypass system with no stat won't push anything through the rad. all you can do is wedge it open inside.

Saint.V8 said:

How do you run without a stat on the 4.0 and 4.6?? it is built into a plastic housing plumped into the coolant system near the bottom of the radiator....is the housing able to be split apart and stat removed as I thought they were moulded in!!

Click to expand...

mangled an old thermostat so that it remained open all the time.

Datatek said:

You just mangle it

Click to expand...

n18rks said:

mangled an old thermostat so that it remained open all the time.

Click to expand...

Oh I see.....

Datatek said:

Just as an experiment, you could try using the aircon fans for cooling and leave the viscous fan off. I can give you a mod to use the aircon fans.

Click to expand...

Not sure what this will prove - i know that i have 100% circulation - what i don't have is a thermostat that opens when driven - i know the thermostat works (tested in kitchen and that i get radiator hot all over).

Are you sure the viscous fan is even locking up as it is supposed to? What sort of temperature are you seeing without the thermostat - and how the blue blazes did you manage to bypass it - three pipes on top and one below .... you 100% certain that you have the correct thermostat fitted as in the later one. Who's thermostat OEM or a cheapo unknown ...

Don't be tempted to run with out the pressure differentials caused by the thermostat are needed for proper circulation and heat transfer throughout the block.

It ain't what we know that gets us into trouble it is what we know for sure that just ain't so ....

Datatek said:

Leaving the cowl off should not cause it to overheat, it does increase fan efficiency but it is as much a safety feature as anything. The diesel will run happily without fan or cowl unless in slow traffic.

Click to expand...

cowl is in place with fan removed.

I suppose your new stat could be duff and failing to remain open. There do seem to be a lot of duff stats around.

Datatek said:

I suppose your new stat could be duff and failing to remain open. There do seem to be a lot of duff stats around.

Click to expand...

tested stat - all working ok - zzr1200 from this forum can round and we tested it together

n18rks said:

cowl is in place with fan removed.

Click to expand...

If the rad is cold when it overheats when driving, something has to be stopping the flow. Even a seized viscous would not over cool the RAD and at the same time allow the engine to over heat, likewise if the fan is not locking up the rad should be red hot unless it boils and vapour locks.

If the coolant boils, flow may stop as the pump will not pump steam so the RAD will soon cool.

n18rks said:

tested stat - all working ok - zzr1200 from this forum can round and we tested it together

Click to expand...

But that would be a static test with no flow pressure from the pump.

n18rks I'II be back in town from tomorrow if your working at home this week let me know and I'II pop in.

BenKenobi said:

Are you sure the viscous fan is even locking up as it is supposed to? What sort of temperature are you seeing without the thermostat - and how the blue blazes did you manage to bypass it - three pipes on top and one below .... you 100% certain that you have the correct thermostat fitted as in the later one. Who's thermostat OEM or a cheapo unknown ...

Don't be tempted to run with out the pressure differentials caused by the thermostat are needed for proper circulation and heat transfer throughout the block.

It ain't what we know that gets us into trouble it is what we know for sure that just ain't so ....

Click to expand...

New viscous fan - air movement increases with engine revs.

New thermostat is OEM - i made sure i paid more for it that i would have normally of done

Temperature gauge sits just above the blue marks on the temp gauge

Datatek said:

If the rad is cold when it overheats when driving, something has to be stopping the flow. Even a seized viscous would not over cool the RAD and at the same time allow the engine to over heat, likewise if the fan is not locking up the rad should be red hot unless it boils and vapour locks.

If the coolant boils, flow may stop as the pump will not pump steam so the RAD will soon cool.

Click to expand...

The coolant i believe is boiling but if this is the case why does the boiling coolant not open the thermostat - hot coolant is passing through the heater matrix therefore being pumped confirmed by getting hot air in cabin and down from the top hose via the by pass hose - either should open the stat?

Datatek said:

But that would be a static test with no flow pressure from the pump.

Click to expand...

correct - how do you do a flow test ?