Which PRT?

[Abott10]

The Lotus owners SELOC site recommends this PRT for the K- Series :~

http://wiki.seloc.org/a/Pressure_Relief_Remote_Thermostat

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


With these cooler winter ambient temperatures, the engine rarely reaches "normal" on the Temperature Gauge now except during longer, higher speed Motorway runs. I suspect the PRT which looks like the original, is not doing its job properly. PEL500110 is the GREY (82c) PRT :~

EBAY Item 231056614293

......whilst its the CREAM (88c) one I have seen on several 75/ZT 1.8t cars.

Decisions, decisions ... any pointers as to which is best to use on my ZT 1.8t greatly appreciated.

[DMGRS]

The ones I have are 82 degrees - and a good few members on here use them with no issues. This one:
PRT - Rover 75 / MG ZT 1.8 K Series (82) (http://www.dmgrs.co.uk/collections/thermostats-and-waterpumps/products/prt-thermostat-rover-75-mg-zt-1-8-k-series-pem100990)

[chipsceola]

Converted mine to PRT when they were available as complete system earlier this year, now fitted with 82C stat and result is running temp of 87/90 instead of previous 96/100C with original 88C stat, does not adversely affect heater warm up or average mpg

[T-Cut]

While the Lotus website (http://wiki.seloc.org/a/Pressure_Relief_Remote_Thermostat) remains about the only place to get info on the various PRTs, it has altered it's advice over the last few years and to an extent describes things that can no longer be followed.

Their earlier advice for 1.8T engines was to fit the buff/cream version. This was said to be the 88C/medium spring temper. Many 1.8Ts came from the factory with this one fitted. Mine did for sure and I always found it reliable, providing 95-100C running whatever the time of year.

I recently swapped it for the black version as an experiment to try to assess the differences. This version was at one time sold by Xpart as the preferred option for the 1.8T. It runs around 5C to 8C cooler across the range, but seems to have a high temper relief spring. In fact I don't think it will open under normal engine speeds. That's mitigated somewhat because all PRTs have a fairly high bleed rate past the secondary (pressure relief) valve. The metal valve itself is perforated with four holes and the plastic seat has two bypass channels.

More recently, the grey type has been recommended by the Lotus site. As noted, they say this one is rated 82C with a soft temper relief spring. I tried various suppliers of the grey version, mainly LR outlets on eBay. These were each returned after I examined the temperature and spring rates. All were 88C and had similar spring temper to the original buff type.

It's my opinion that the colours of the currently available PRTs (especially the grey one) probably bears little relationship to the original MGR temperature and spring rate coding. Indeed, not one of the main LR suppliers even understood what I was talking about. They're simply sold as 'in-line' thermostats. Pressure relief doesn't figure in LR's thinking. Additionally, many PRTs now seem to be foreign imports, where the original specifications have become blurred or homogenised.

With these cooler winter ambient temperatures, the engine rarely reaches "normal" on the Temperature Gauge now except during longer, higher speed Motorway runs. That suggests the stat has failed IMO. The engines with PRTs run at roughly the same temperature summer and winter in my experience.

I suspect the PRT which looks like the original, is not doing its job properly. PEL500110 is the GREY (82c) PRTIf it's grey, I doubt it was factory fitted, but anything's possible. It will be the first original one I've read about.

Decisions, decisions ... any pointers as to which is best to use on my ZT 1.8t greatly appreciated.Considering my personal experiences with the PRT/1.8T, I'd say the buff version gives a reliably warm performance that responds well to the throttle (engine revs/pump pressure). The black one acts like a standard 88C stat with little pressure relief and runs somewhat cooler all year round. The grey version seems to be something different from what it was originally. I won't be fitting one, even experimentally, unless I can find one of the originals with a measurably low spring rate. That seems a remote possibility now.

TC

[The Mighty Quinn]

I changed to the grey PRT (Lotus recommended one) about a month or 2 ago from the original cream coloured one and have found absolutely zero difference in the running or operation of the car - just that the coolant temps in normal driving conditions are down about 10 degrees from circa 97 to circa 87 - which I figure can't be a bad thing.

Must say though, the cream coloured PRT never caused me any trouble..

It seems that both work ok (so far anyway!).

[stevesav]

The ones I have are 82 degrees - and a good few members on here use them with no issues. This one:
PRT - Rover 75 / MG ZT 1.8 K Series (82) (http://www.dmgrs.co.uk/collections/thermostats-and-waterpumps/products/prt-thermostat-rover-75-mg-zt-1-8-k-series-pem100990)

I have to agree with this, I had bought a prt from somewhere else but still overheating, fitted a new rad but no joy, then got told that maybe the prt I bought might be faulty, do got a new one from DMGRS & it did the trick, temp now between 82-84, brill:icon_lol::icon_lol::icon_lol:.

[DMGRS]

I have to agree with this, I had bought a prt from somewhere else but still overheating, fitted a new rad but no joy, then got told that maybe the prt I bought might be faulty, do got a new one from DMGRS & it did the trick, temp now between 82-84, brill:icon_lol::icon_lol::icon_lol:.

Thanks for the recommendation. I must stress that mine are 82 degrees, despite the 'buff' colour suggesting they are 88. :)
Plenty on the shelf, as I've noticed a lot must be sticking open - I've been inundated with orders for them recently!

[T-Cut]

I changed to the grey PRT (Lotus recommended one) about a month or 2 ago from the original cream coloured one and have found absolutely zero difference in the running or operation of the car - just that the coolant temps in normal driving conditions are down about 10 degrees from circa 97 to circa 87 - which I figure can't be a bad thing.
Must say though, the cream coloured PRT never caused me any trouble.

From my tests on two Land Rover grey versions, they aren't equivalent to the original grey specifications set out on the Lotus Wiki site. The only way to get a grey PRT is to use the LR one, which I subsequently found was developed by LR themselves for the Freelander. This was originally fitted with the buff version as used by MGR in the 1.8T. I wanted to replace my current black one for a grey one. That would complete my experimentation covering the original buff PRT with the current black and grey types. I found the relief spring tension of the grey one equal to, if not slightly greater than the buff type. These are supposedly medium (buff) and low (grey). I asked two LR parts suppliers if they stocked the 82C/low tension one and they didn't understand what I was talking about. There is no reference to pressure relief in LR's literature and suppliers haven't even heard of it. Upshot is, PRTs are no longer produced with soft, medium and high pressure relief rates. They're simply in-line/remote thermostats sold on temperature rating like ordinary stats. Unfortunately, I didn't measure the spring tension on the black PRT before I fitted it four years ago. This was the one sold by Xpart for the 1.8T at the time. From my driving tests, it doesn't exhibit any pressure relief at any engine speed I'd normally use. This tallies with other web info I found which confirms the black stat has a virtually irresistable relief spring tension.

TC

[DMGRS]

Rather than being grey, I think it's just a poor picture of a white/buff item. :(
Also, in the listing it mentions 92 degrees - if you look in the connections of the thermostat, you should be able to see the temperature stamped into the metal insert.

[T-Cut]

The temperature rating may or may not be stamped on the stat anywhere. Some people report seeing it visible on the main valve when viewed through one of the ports. That may depend on the relative positioning of the inner and outer parts when the case halves are bonded together. It's certainly not visible on my OEM buff one.

I've also dissected another donated OEM buff PRT and again there's no familiar temperature indicator. This photo shows the only markings on it (this is the main/primary valve annulus with rubber coated valve disc below).

http://i5.photobucket.com/albums/y191/waveguide/Cooling_System_Stuff/PRT_Stuff/DSCF3256_zps1d7213d2.jpg

Clearly, the '43' seen here isn't related to the opening temperature.
The annulus also has a jiggle/ball valve for air bleeding. This must be positioned at the top in the fitted stat so the innards may well be bonded into the case in one specific orientation.

The Black PRT I have fitted atm wasn't examined unfortunately. However, the two grey versions from Land Rover suppliers (PEL500110) both had 82°C stamped on the end of the spindle. This was hollow ended where the metal disc relief valve is fitted, not the primary thermostatic valve. If you survey this part number on eBay you'll find they may be grey or white and described as anything from 82°C to 92°C!
And never a mention of 'pressure relief'.

This is a photo of the spindle end (buff version).

http://i5.photobucket.com/albums/y191/waveguide/Cooling_System_Stuff/PRT_Stuff/DSCF3252_zps3ed946ed.jpg

The spindle has a slightly larger diameter on the LR models and the hollow end was flat bottomed where the 82°C was stamped.

EDIT: Note the four holes in the relief valve. This allows a permanent bleed from the head into the stat when the primary valve is fully open to flow from the radiator bottom and the bypass/relief disc is hard on its seat. The relief valve seat also has cutaways to enhance this bleed even more. You can see this here. This is one half of the outer case.

http://i5.photobucket.com/albums/y191/waveguide/Cooling_System_Stuff/PRT_Stuff/DSCF3246_zps05ef0a64.jpg

There's more to the operation of a PRT than we might have imagined.

TC