Pressure Relief Remote Thermostat

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

MG part number for PRRT kit is PCH003320. This kit is for the MGF wich 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 one hose joiner in addition.

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.

For DIY instructions on fitting please see the how to fit a PRRT guide.

External links

• http://web.tiscali.it/elise_s1/index.htm
• http://111ti.free.fr/elise_cooling_jul2005/
• http://forums.seloc.org/viewthread.php?goto=2344458
• http://forums.seloc.org/viewthread.php?tid=110181&page=4
• http://www.mgf.ultimatemg.com/group2/engines/development_history_of_the_K.htm
• http://www.mgf.ultimatemg.com/group2/common_problems/hgf_pages/why_do_hgfs.htm