What Temperature is to high?

[RobPlews]

Originally Posted by kaiser

I don't think your test shows a faulty thermostat.!
I have never dropped a thermostat into boiling water, but I heat it with the water.
If slowness to react was a criterion then it would seize to be important once hot!
You don't state if both thermostats open fully, that is normally about 10mm.
That is the only possibility I can see.

I agree there is normally a lot of heat in the heater on a 1.8T, when it is hot outside!

I do. A thermostat that doesn't react quickly enough is just like one that doesn't open at all... right up to the point that is does and then it just saves the day. If it doesn't open promptly when you put your foot down you are going to have problems.

It was done quick scientifically with just one side in the hot water - just as they run in the car. A very fair test.

I also had a few other standard thermostats around and they all opened in a similar time frame but not the suspect one.

They all opened about 10mm as you say. But one of them took so much longer to get there.

We will find out when the new one arrives.

[COLVERT]

Originally Posted by kaiser

I don't think your test shows a faulty thermostat.!
I have never dropped a thermostat into boiling water, but I heat it with the water.
If slowness to react was a criterion then it would sieze to be important once hot!
You don't state if both thermostats open fully, that is normally about 10mm.
That is the only possibility I can see.

I agree there is normally a lot of heat in the heater on a 1.8T, when it is hot outside!

I guess you mean--cease--rather than seize up.---

[TourerSteve]

Originally Posted by RobPlews

I do. A thermostat that doesn't react quickly enough is just like one that doesn't open at all... right up to the point that is does and then it just saves the day. If it doesn't open promptly when you put your foot down you are going to have problems.

It was done quick scientifically with just one side in the hot water - just as they run in the car. A very fair test.

I also had a few other standard thermostats around and they all opened in a similar time frame but not the suspect one.

They all opened about 10mm as you say. But one of them took so much longer to get there.

We will find out when the new one arrives.

Testing a PRT thermostat for opening as you would a normal thermostat proves that the thermostat is opening but does not guarantee correct operation on the car. PRT Bypass spring type condition of water pump and expansion cap also play a part in the operation
Once fitted to car , fluid mechanics come into play. Fluids will naturally follow the path of least resistance . Restriction to flow creates pressure but if PRT Spring pressure to great it cannot overcome it to open bypass . Hence if the PRT bypass spring tension is too great the coolant will prioritise the heater circuit rather than the bypass circuit and low flow of coolant in the bypass will possibly not see a temperature high enough to open the thermostat sufficient to allow enough coolant flow around the radiator . Hence running temperature higher even though your radiator and bottom hose feel cold .The lower your engine speed the worse the problem is , as increasing engine speed, increases flow and overcoming the spring pressure in the PRT bypass spring . A lower spring pressure opens the bypass with less engine speed .
On a correct operating system once thermostat open Coolant will flow through the radiator ,close PRT bypass and bottom hose and radiator will feel warm
As said on my first post the PRT you fitted which was malfuntioning was probably due to spring pressure to great on the bypass
Landrover also fitted the K series to the original Freelander and I take it after issues fitted a lower spring rated PRT which is the one recommended .

[ricardo65]

Originally Posted by TourerSteve

Testing a PRT thermostat for opening as you would a normal thermostat proves that the thermostat is opening but does not guarantee correct operation on the car. PRT Bypass spring type condition of water pump and expansion cap also play a part in the operation
Once fitted to car , fluid mechanics come into play. Fluids will naturally follow the path of least resistance . Restriction to flow creates pressure but if PRT Spring pressure to great it cannot overcome it to open bypass . Hence if the PRT bypass spring tension is too great the coolant will prioritise the heater circuit rather than the bypass circuit and low flow of coolant in the bypass will possibly not see a temperature high enough to open the thermostat sufficient to allow enough coolant flow around the radiator . Hence running temperature higher even though your radiator and bottom hose feel cold .The lower your engine speed the worse the problem is , as increasing engine speed, increases flow and overcoming the spring pressure in the PRT bypass spring . A lower spring pressure opens the bypass with less engine speed .
On a correct operating system once thermostat open Coolant will flow through the radiator ,close PRT bypass and bottom hose and radiator will feel warm
As said on my first post the PRT you fitted which was malfuntioning was probably due to spring pressure to great on the bypass
Landrover also fitted the K series to the original Freelander and I take it after issues fitted a lower spring rated PRT which is the one recommended .

thanks for the indepth and easy to understand explanation of the operation of the PRT Touersteve you recommended it to me and others a while ago so I fitted the freelander PRT to my 1.8 turbo and can't praise it enough and would recommend it to anybody a little more expensive but well worth it

[T-Cut]

Originally Posted by ricardo65

- - - I fitted the freelander PRT to my 1.8 turbo and can't praise it enough

What colour is it and what relief spring rating does it have? When I asked a well known Land Rover distributer about their recommended grey flavour of PRT, they didn't understand the question, let alone the answer. In fact I doubt there's a PRT supplier anywhere that does. Have you observed the relief mechanism in action, perhaps using the Diagnostic Mode temperature display?

TC

[TourerSteve]

Originally Posted by T-Cut

What colour is it and what relief spring rating does it have? When I asked a well known Land Rover distributer about their recommended grey flavour of PRT, they didn't understand the question, let alone the answer. In fact I doubt there's a PRT supplier anywhere that does. Have you observed the relief mechanism in action, perhaps using the Diagnostic Mode temperature display?

TC

I don’t know why your Landrover distributer doesn’t have the same information on these part numbers as Rimmers. If you note these PRT part numbers are listed as Landrover as well as Rover parts . Unfortunately as you state visually apart from colour there is no markings on a lot of the PRT’s making the choice a lottery , particular pattern parts .That's why I would always recommend buying genuine parts . We had issues with a 1.8T running hot went through the system suspected the PRT changed it Wasn’t happy with new one as coolant didn’t seem to be circulating correctly and looked at alternatives , Making an educated decision noting the lower temp and spring pressure tried the PEL500110 .
Resulting in an engine that normally runs at 88-89 C In standing traffic coolant will raise to fan cutting in and in less than a minute lowers to fan cut out .
The PEL500110 PRT’s that we have are all Grey
We run 3 cars with the same set up and they all perform the same
2 x 1.8t and 1x 1.8
The part details below are the genuine parts, the information is there on the website


Thermostat Recommended

https://rimmerbros.com/Item--i-PEL500110
Thermostat Housing - PEL500110 – Genuine
Product Description
82°C, soft spring rate.
This is the PRT usually suggested for retro conversions on MGFs and pre-2003 MG TFs.

Rover 75/MG ZT Pipes and Hoses - 1800 NA PRT | Rimmer Bros
https://rimmerbros.com/Item--i-PEM100990
PEM100990 is a PRT (pressure release thermostat) for a MGTF LE500.
87°C, medium spring rate.

Rover 75/MG ZT Pipes and Hoses - 1800 Turbo PRT | Rimmer Bros
https://rimmerbros.com/Item--i-PEM101021
Product Description

87°C, medium spring rate.

Fits Rover 200, Rover 400, Rover 600, Rover 75, MG ZT, MG TF

Not suitable for Rover 25 & MG ZR versions as the thermostat is oil cooler mounted.

[T-Cut]

Originally Posted by TourerSteve

Thermostat Recommended
https://rimmerbros.com/Item--i-PEL500110
Thermostat Housing - PEL500110 – Genuine
Product Description
82°C, soft spring rate.

This is the grey version that I bought from Land Rover because of the reported 'soft' relief spring. I wanted to compare it with the factory fitted buff type which provided mid- to hi-90s running and relief valve operation around 2000rpm. On measuring the relief spring loading using a 1 gram precision balance, it was almost exactly the same as the buff one I had already. From the valve opening force measured by the balance, I calculated the hydraulic pressure needed to start valve opening in the enginewas slightly over 2psi. So, it wouldn't have changed anything in regard to the pressure relief point I was getting already and I returned it unused. That's when I asked LR about their PRT relief spring ratings and they looked at me blank.

Rover 75/MG ZT Pipes and Hoses - 1800 NA PRT | Rimmer Bros
https://rimmerbros.com/Item--i-PEM100990
PEM100990 is a PRT (pressure release thermostat) for a MGTF LE500.
87°C, medium spring rate.

This looks like the factory fit buff version on the 1.8 turbos.

Rover 75/MG ZT Pipes and Hoses - 1800 Turbo PRT | Rimmer Bros
https://rimmerbros.com/Item--i-PEM101021
Product Description
87°C, medium spring rate.

Is the black type which Rimmer suddenly began listing for the 1.8Turbo around 2008 after listing the OEM buff one for several years after the 1.8T was introduced. Back then, I bought the black one and fitted it as a test to see how it compared. Contrary to Rimmer's current description, it was at the time as an 82C stat which was part of the attraction, experimentally. I still have this one fitted and the engine does indeed run about 8 degrees cooler across the range. However, the relief pressure must be considerbly higher than the stated 'medium' because unlike the 'medium' rated buff version, I've yet to observe the pressure point via engine revs. From my perspective, I'd rate it a much higher relief pressure than the OEM buff one.



So, over the years since MGR's demise, my conclusion is that the principles on which the PRT was introduced have been virtually abandoned by manufacturers. Colour codings soon went completely out the door and very few suppliers actually identify their PRTs by both temperature and relief spring tension. Rimmer's descriptions don't really stand scrutiny on a historical basis, I believe we're comparing apples with oranges nowadays. Just because an engine operates within a particular temperature range tells very little, if anything, about how the pressure relieve system is or isn't operating. They're simply different thermostats. Outside the running of the 1.8T on a racetrack, the necessity of the PRT remains debatable IMO, especially when you can't easily verify what's written on the box. The original motivation to reduce thermal gradients and resolve the 1.8's Achilles Heel head gasket was very effectively pushed aside by the 'ultimate solution' of an MLS gasket, uprated oil rail and higher torque bolts. I reckon few people are really interested in PRTs nowadays.



TC

[TourerSteve]

Quote:
Originally Posted by TourerSteve
Thermostat Recommended
https://rimmerbros.com/Item--i-PEL500110
Thermostat Housing - PEL500110 – Genuine
Product Description
82°C, soft spring rate.
This is the grey version that I bought from Land Rover because of the reported 'soft' relief spring. I wanted to compare it with the factory fitted buff type which provided mid- to hi-90s running and relief valve operation around 2000rpm. On measuring the relief spring loading using a 1 gram precision balance, it was almost exactly the same as the buff one I had already. From the valve opening force measured by the balance, I calculated the hydraulic pressure needed to start valve opening in the engine was slightly over 2psi. So, it wouldn't have changed anything in regard to the pressure relief point I was getting already and I returned it unused. That's when I asked LR about their PRT relief spring ratings and they looked at me blank.
I can under stand you have gone down the route of testing opening force but can it be accurate enough to determine a difference to what they class as low or medium spring .In practice a small change in pressure can determine between by pass opening or not . Dealerships would only have the information supplied with PRT’s as per Rimmers .
Quote:
Rover 75/MG ZT Pipes and Hoses - 1800 NA PRT | Rimmer Bros
https://rimmerbros.com/Item--i-PEM100990
PEM100990 is a PRT (pressure release thermostat) for a MGTF LE500.
87°C, medium spring rate.
This looks like the factory fit buff version on the 1.8 turbos.
Would agree there . This was the one we had problems with and would say you need in excess of 2000rpm to operate bypass valve meaning town traffic engine was running hot . A thrash down an open road dropped running temperature ,and confirmed full circulation of cooling system by a warm bottom hose between radiator and PRT , Lower than 2000rpm bottom hose between radiator and PRT remained cold

I take it this was the equivalent of standard fit from the factory

Quote:
Rover 75/MG ZT Pipes and Hoses - 1800 Turbo PRT | Rimmer Bros
https://rimmerbros.com/Item--i-PEM101021
Product Description
87°C, medium spring rate.
Is the black type which Rimmer suddenly began listing for the 1.8Turbo around 2008 after listing the OEM buff one for several years after the 1.8T was introduced. Back then, I bought the black one and fitted it as a test to see how it compared. Contrary to Rimmer's current description, it was at the time as an 82C stat which was part of the attraction, experimentally. I still have this one fitted and the engine does indeed run about 8 degrees cooler across the range. However, the relief pressure must be considerbly higher than the stated 'medium' because unlike the 'medium' rated buff version, I've yet to observe the pressure point via engine revs. From my perspective, I'd rate it a much higher relief pressure than the OEM buff one.

[COLOR="red"]Never had any dealings with this PRT so unable to comment
Interesting about the comments on your PRT
I would like to ask what makes you perceive that your PRT bypass relief is a lot higher than the beige one ?
As my perception is that you need coolant circulating round the bypass to open the thermostat , Your perception may be different ?

So, over the years since MGR's demise, my conclusion is that the principles on which the PRT was introduced have been virtually abandoned by manufacturers. Colour codings soon went completely out the door and very few suppliers actually identify their PRTs by both temperature and relief spring tension. Rimmer's descriptions don't really stand scrutiny on a historical basis, I believe we're comparing apples with oranges nowadays. Just because an engine operates within a particular temperature range tells very little, if anything, about how the pressure relieve system is or isn't operating. They're simply different thermostats. Outside the running of the 1.8T on a racetrack, the necessity of the PRT remains debatable IMO, especially when you can't easily verify what's written on the box. The original motivation to reduce thermal gradients and resolve the 1.8's Achilles Heel head gasket was very effectively pushed aside by the 'ultimate solution' of an MLS gasket, uprated oil rail and higher torque bolts. I reckon few people are really interested in PRTs nowadays.

Obviously Since MGR,s demise you have lost the technical support for these cars and as such we are left between us to iron out ongoing issues and technical gremlins .
As for the PRT,s they have got very diluted in terms of specifications and quality as most if not all will be pattern parts We inherited them with the cars so to keep them running we have to find solutions
That is why I added the recommendation for that PRT after the problem we had with a 1.8T. knowing the issues we had with the minefield of pattern parts. Doing a bit of research favoured the grey PRT PEL500110 which seems to be a favourite of the MG TF boys as well .
The grey PRT PEL500110 may not be the perfect solution but it has now proved satisfactory service in quite a number of cars which had been fitted with the Beige original PEM100990
A cooling system should flow around the full system when a car is fully warmed up meaning all should show signs of heat to confirm flow

[ricardo65]

Originally Posted by T-Cut

Have you observed the relief mechanism in action, perhaps using the Diagnostic Mode temperature display?

TC

to keep things simple my 1.8 t has the PEL500110 PRT fitted it also has the Han's digital temp gauge fitted the normal running temp is 88° when in stop start traffic say 20 minutes plus it usually sits 94-96° I've never had the low speed fan come on as yet and yes it does work the car is usually used in the summer months this is why I recommend this PRT the only other thing i will add is the car also was fitted with a new radiator along with the PRT