[Rowant]

Last year my previous P38 was written off in an accident and I have finally bought another one that I like - '96 and only 64K kilometers.
It has developed an overheating problem. I changed the fan hub but no improvement. I removed the thermostat and put in a new one - that was even worse. I checked the old unit by pouring boiling water directly into the inlet tube and it took about 30 seconds before it would start to open. Then it flowed a good amount of water.
I checked the new unit and it wouldn't even open - faulty!! Put the old unit back in the car and warmed up the engine. The needle has gone up to the 6th mark and the thermostat hasn't opened yet - the bottom tank and rubber connecting hose are both cold.
Does anybody know about how long it should take for the thermostat to react to heat? The 6th mark equates to well over 100* .

Thanks for any information.

 

[Escape]

You should try to determine the source of the overheating before replacing parts. Do you have good flow, is the radiator clear internally as well as externally, is there a possibility of head gasket failure?
When replacing the thermostat, you might end up with an air bubble. Most of the time the P38 is easy to bleed, but recently I've had one with an airlock that caused overheating. It took a lot of effort to clear. In the end I ran it open circuit for a bit, with the heater hose disconnected while constantly refilling and that solved it.

Filip

 

[Rowant]

I am trying to work through this by a process of elimination.
No coolant loss or puddles on the ground. When the engine is hot the top hose is still soft - I think not a head gasket problem (hopefully).
I changed the fan clutch for a spare and there was no difference - both appear to be good.
I removed the thermostat and put in a new one. That didn't even open - faulty!!
I poured boiling water directly into the old thermostat and it began to open after about 30 seconds - eventually flowing a good amount of water. The same test on the new faulty unit never even opened it. I will return it tomorrow.
I have used a hose connected to the radiator and it flows a lot of water. I have also flowed through the radiator from back to front and everything appear to be good.
I am now suspecting that either my thermostat has an intermittent fault or it is opening too slowly - hence my question.
I filled and bled the system according rave.
I think that if I had an airlock under the thermostat it would be cleared when the unit opened and allowed hot coolant through.

 

[Daf11e]

Is your water pump Ok?

 

[xrav22]

I agree you need a water pump to put the pressure to your top hose.

 

[Rowant]

When I wrote that my top hose is soft I meant that it is not rock hard as some have experienced. I should have put that it is reasonably firm to the squeeze.
The place I got the faulty unit from is a well known indy importer and service company for LR's over here. The also told me to pull out the radiator as next option - don't worry about the pump yet.
I am beginning to doubt their credibility.

 

[Escape]

Rowant, looks like you did a thorough job. Just don't be too quick to assume flow is good and there are no airlocks. We spent a couple of days looking for a cause, finally turned out to be an airlock.

When does the car overheat? Under load or stationary? The latter is likely to be a problem with airflow. Radiator could explain both.

Filip

 

[dave3d]

The traditional way to test a thermostat is to put it into a saucepan of water on the stove with a thermometer in it, so you can see what is going on. As the temperature rises the thermostat suddenly opens up. It happens in like about 10 seconds. All the brass thermostats I have come across have the temperature stamped on them, usually 86 deg C, but I have seen some with 88 deg C (not on a p38 though). It should be a sharp change, say 84 deg fully closed, then suddenly fully open at 86 deg. They do stick or have hysteresis when worn, so test it cooling down as well. I had one on my diesel that was fully open at the right temperature but stayed open way down to 70 deg or so before being fully closed.
There are also a lot of cheap radiators knocking about that don't have sufficient heat transfer area. Maybe a previous owner has fitted one.

 

[Sloth]

Genuine LR V8 thermostats open at a really high temperature - 95-96c on the last couple I've tested in the saucepan method - and confirmed on nanocom on the vehicle.

Some cheapies out there start opening at 82c, including the one in my vehicle (Britpart branded).

 

[Rowant]

Thank you Filip. The gauge temperature pauses at position 4 on the gauge for a while when warming up - then starts climbing again. This happens when stationery.
My unit took about 30 seconds to start to open and then only very gradually. And then another 20-30 seconds to open to a good flow. This is with boiling water poured directly into the to inlet nozzle. I don't have a thermometer and my wife would kill me if I used a pot on the stove. I just used hot water to show that it is, at least, opening at all. Because it was taking so long I was a little concerned that it might be faulty.
I will investigate whether my radiator is genuine or a replacement item. The faulty thermostat that I was sold is in an 'all-makes' box and has no part number markings. Where do I find factory part numbers on the radiator?

Rowan

 

[dave3d]

Sloth said:

Genuine LR V8 thermostats open at a really high temperature - 95-96c

I am surprised it is so high but then again I have the diesel. Thermostat temperatures seem to vary widely these days.
Apparently most Japanese cars 170-180 deg F (77-82 deg C) and some BMW's 226 deg F (108 deg C).

Rowant:
I know the feeling, SWMBO has caught me with car parts in the dish washer before today. Use a camping stove in the back garden and an old can. Were you never in the boy scouts?
There may be a L/R sticker left on the radiator somewhere or else take a picture and try to match it with those you can buy online.
Also "All Makes" is the same as Terafirma who usually make good stuff. Or maybe with thermostats they just buy them in.

 

[Richard_G]

The gauge temperature pauses at position 4 on the gauge for a while when warming up - then starts climbing again. This happens when stationery.

I had one car that was doing exactly that, found insufficient flow, changed the water pump and problem solved. If it's an unknown, I'd change the radiator too just to be on the safe side.

 

[pwood999]

New kitchen kettles are cheap these days . . . . get a nice new one for the kitchen (& get wife points), and then use the old one in the workshop like I do. Submerse the thermostat & switch on. It should open just before the water boils. Lift it out with pliers and it should close in a minute or so.

But ++1 on replace water pump. There's two versions (plastic & metal impellers), which both wear out and don't pump as well when old.

Finally make sure you bleed according to RAVE & clear out the expansion tank pipe properly.

 

[Daf11e]

When the water pump went on mine I couldn't even bleed the system it overheated so quickly.

 

[xrav22]

I Have not had an issue with bleeding since I filled the radiator, engine from the top hose now. That should be in the manual. But I still have to drive to get the heater core rocking.

 

[Escape]

From Rave: the thermostat is closed below 80°C/176°F, starts to open from 80 to 84°C (176 to 183°F) and is fully open at 96°C/204°F. Which means you should have a coolant temperature between 80 and 96°C if everything is working as it should.

 

[Rowant]

I returned the new thermostat and the chap tested it as well - not working. He told me not to throw parts at the problem until I had confirmed that my car really is overheating. I bought an IR thermometer and the highest temperature I could find was hovering at 90*.

He told me that it isn't overheating after all and will be a sender problem - this seems logical. To confirm this I should warm up the engine and then turn on all electrical accessories - heater, lights, brake pump and anything else I can - if the termperature climbs further then it is an electrical issue and he has a fix for me.
He said that later gems engines have a different fitting for the top hose to the intake manifold and their sensor (different item) sits there - that is the cure for my problem.

Has anybody heard about this later model fitting and might it really solve things?

 

[Richard_G]

Having a 96 (TA prefix VIN), a 97 (VA prefix VIN and a 98 (WA prefix VIN) here at the moment I've just had a look to compare them. The 96 does have a different inlet manifold with the coolant temperature sensors being different. One of them only has a single wire going to it so it is grounded through the body. This, if the ground connection is poor, would cause the gauge to read incorrectly but increased resistance would cause the gauge to read low not high. Oddly RAVE shows the same two wire sensor on all petrol engined cars but the diesel is shown as having a single wire sensor up to 97. Reading back through the thread, you say it is overheating but not showing any signs of an overheat. Are you simply going on what the gauge is telling you? If it was actually overheating the hoses would be hard, excess coolant would be pushed out of the header tank overflow and you would be able to hear it boiling inside the engine. Have you tried putting an OBD code reader that can display live values and seeing what temperature is being reported? Although not fully OBD compliant, a reader will still work on a GEMS, even the very early ones. I used this method to check the cooling system on the 96 as the gauge reads lower than the other two but the OBD readings are correct, suggesting a bit of high resistance in the ground connection.

 

[Rowant]

Because my previous P38 NEVER went above the 4th mark I am a bit worried that my new one has a problem. As the IR reading was only 90* I will have to believe that it is not really overheating and is just a system fault relating to the sender.

The gauge sender on my car is the single wire sensor on the top front of the intake manifold - the other 2 wire is for the ECU. Did later gems engines move the single wire gauge sender from the manifold to the top hose connection fitting? I can't find any reference anywhere to this 'later' mounting position.

If nobody has ever heard about this later position I will consider just replacing my existing sender - the best quality available of course.

Rowan

 

[Eric Lording]

Judging from my experience with the latest aluminium radiators containing small cooling pipes and swirl initiators in those cooling pipes, your problem will be fixed with a new genuine radiator.
I base this on two P38's needing new radiators and my L322 needing a second radiator late last year, the second in 10 years.
I chased the cooling system overheat problem in my first P38 for months before I had run out of things to replace; except the radiator as it was the most expensive to replace, but replacing the radiator fixed all my problems.
Sorry to give you bad news, but I say this with bitter experience and a lot of blood letting and anguish. Now I just replace the radiator at the first sign of over heating or water loss. A damaged engine costs a lot more.