Pressure Relief Remote Thermostat

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A Pressure Relief Remote Thermostat (PRRT), or sometimes just PRT, is used to increase the amount of coolant flowing around the engine. The PRRT has a bypass valve opening when the coolant pump is flowing too much coolant for the radiator circuit. This valve is reducing pressure difference inside the whole circuit, achieving at the same time a more constant temperature inside the engine.

Note: The acronym PRT means Pressure Relief Thermostat. This setup was developed by Bill Hutchins and used by Rover, MG and Landrover, it has been in use in mid engined cars for 25 years, and an Elise system was previously developed by Simon Scuffham when racing his k-series engined elise. PRRT is actually a misnomer (albeit harmless), allegedly invented by one of the members of the Seloc forum. The PRRT acronym may not actually be recognised by anyone outside of the Seloc forum (including anyone involved in the design, manufacture or assembly of the device) though is perhaps a more accurate description as the second R refers to remote.

PRRT Colours

  • Cream is 87°C With Medium Spring: first being used on FreeLander & MGF/TF.
  • Black is 82°C With Hard Spring: Not suitable for Rover K engines.
  • Grey is 82°C With Light Spring: Latest being used on Freelander (MGF/TF ?). Land Rover replace the old stat (87°C) with this one if they have to open the coolant circuit. THIS IS THE ONE YOU WANT !!!

[information added by Yvo Tuk from]
The above mentioned colour information is outdated.

There are four manufacturers of the actual remote thermostat units nowadays (2015). Some of them stick to the original colour scheme and some deliver their thermostats in the same colour for every temperature. We currently ship kits with cream coloured 82°C thermostats. We've also seen black and yellow thermostats in 82°C.

The temperature is stamped in the actual thermostat which can be seen through one of the hose connections.

[information added by Lindsay Porter, Porter Publishing - see] 1. The thermostat temperature digits are visible through the top hose connection but are *extremely* difficult to see - small and on the outer rim of the thermostat. 2. The genuine Land Rover grey thermostat has both the correct temp AND the correct pressure setting. There is no way of checking the latter by observation. 3. If you fit the wrong colour, you won't know if the pressure is correct (even after checking the temp.) and in future, a mechanic won't be able to correctly identify the PRT fitted to your engine.

PRRT Part Numbers

PCH001190 Land Rover cream PRRT kit (including all the hoses and clips needed to make it fit). It is meant to be fitted on a Freelander. (BUY this for an early S1)

PEL500150 Land Rover Part grey PRRT kit (full hoses kit, similar to PCH001190 but with a non useable plastic elbow with small takeoff). Not easy to adapt to the Elise. This kit may also be difficult to obtain.

PCH003320 MG cream PRRT kit. This kit is for the MGF which cooling system is very close to the Elise's so it requires less modifications than the Land Rover kit. It's also cheaper and only requires the addition of a piece of aluminium tube as a hose joiner, which can be cut from a discarded tube from the original system. (BUY this except early S1)

PEL500110 Land Rover grey PRRT (standalone) (BUY this)

PEM101020 Rover part number for both Black and Cream PRRT (standalone) - the fact two different thermostats share the same part number could cause some confusion. The downside with the cream PRRT is that (unless at temperature?) the stat won't open below 1500-1750 rpm due to the spring rate.

PEL000040 a metal polo mint replaces the old thermostat in the housing which pulls left out of the water pump before disassembly (BUY this)

PEM00020P is a complete new dummy thermostat assembly with PEL000040 fitted. It also includes the two O rings for insertion of the assembly into the water pump.

For DIY instructions on fitting please see the Fit a PRRT guide.

PR(R)T for Dummies

What parts are needed:

Early S1 (Upper aluminium water rail)

  • Land Rover Freelander kit with cream thermostat (88°C): PCH001190 from Land Rover
  • Thermostat blanking plate (the seal comes with it): PEL000040 from Land Rover or MG-Rover
  • Optionnal: Grey thermostat (82°C, lighter springs): PEL500110 from Land Rover
  • Hose Joiner 32 mm diam. x?
  • Hose clips 32 mm diam. x?

For fitting, go there:

S2 and Late S1 (Lower Aluminium water rail)

  • MG-Rover MGF CVT automatic kit with cream thermostat (88°C): PCH003320 from MG-Rover
  • Thermostat blanking plate (the seal comes with it): PEL000040 from Landrover or MG-Rover
  • Optionnal: Grey thermostat (82°C, lighter springs): PEL500110 from Landrover
  • Hose Joiner 32 mm diam. x1
  • Hose clips 32 mm diam. x?

Fitting modifications

Don't take values as a gospel, go progressively:

A guide for fitting MGF kit can be found here:

S2 111S with factory oil cooler and recirculation pump

The Elise Parts PRRT needs modification of the coolant circuit in order to work properly and also give flow to the heater matrix. Basically the T section above the recirc. Pump is connected directly to the heater return matrix. The reservoir hose is then connected to a new T which also connects to the oil cooler outlet and the old thermostat housing. Oem hosrs are discarded. This gives a much better flow for lower temps and working cooling circuit. Read more here:


  • Can I just replace the original thermostat without changing hoses?
    • => No you can't. The thermostat wouldn't fit to begin with, and it requires a different circuit setup to work.
  • What do I use if I have / I want to fit an oilcooler?
    • => Go for the "Early S1" list. The landrover Kit has more hoses to play with, it will be easier to adapt. Have a look at Carlo's site (Elise S1) for examples.
  • Isn't there a Kit with the grey (82°C) so I don't have to buy it separetly?
    • => Yes, LandRover has a Freelander kit comming with the Grey stat. It's ref is PEL500150. It's apparently harder to adapt to the elise because of different hoses/elbows. Beside, most of the cost of the kit comes from the hoses. So you'd better choose the right hose kit and them change the stat.

External links