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 !!!

Land Rover Part number for PRRT kit with cream stat (including all the hoses and clips needed to make it fit) is PCH001190. It is meant to be fited on a Freelander.

Land Rover Part number for PRRT kit with grey stat (full hoses kit, similar to PCH001190 but with a non useable plastic elbow with small takeoff) is PEL500150 (this kit may however also be difficult to obtain).

MG part number for PRRT kit is PCH003320 with cream stat. 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.

Land Rover part number for grey stat (standalone) is PEL500110

Rover part number for both Black and Cream stat (standalone) is PEM101020 - the fact two different thermostats share the same part number could cause some confusion.

The downside with the cream PRRT is that the stat won't open below 1500-1750 rpm due to the sping rate.

A thermostat blanking plate part number PEL000040 is also needed to replace the old stat or a complete new dummy thermostat assembly can be installed (PEM00020P), which is a complete thermostat housing with the blanking plate fitted and also including the two O rings for connection to the water pump and water pipe.

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): 

 _ LandRover Freelander kit with cream thermostat (88°C): PCH001190 from LandRover
 _ 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. x?
 _ Hose clips 32 mm diam. x?

For fitting, go there: http://forums.seloc.org/viewthread.php?tid=104578&page=1

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?

As for fitting modifications (don't take values as a gospel, go progressively): http://gallery.seloc.org/albums/userpics/26904/Adapt_kit_MGF_origine_et_modif.jpg http://gallery.seloc.org/albums/userpics/26904/Adapt_kit_MGF_a_la_longueur.jpg

F.A.Q.

_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 exemples.

_ 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

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