Let's talk K-series engine temperatures...

[skydragon]

I've been reading through some old threads regarding coolant temperatures on K-series and a few things puzzle me.

 

background;

 

On a K-series, whether you have a normal thermostat fitted, or a PRRT fitted, the thermostat is fitted on the inlet side of the engine.

 

When up to temperature, hot coolant is fed into the engine and this coolant temperature entering the engine is determined by the thermostat (providing that the water pump and radiator are working ok).

 

So in the case of a 82 deg thermostat, or a 82 deg PRRT unit, the coolant entering the engine should be at 82 deg C.

 

The engine is hot and the purpose of the coolant is to take heat away from the engine and cool it. So, if we have 82 degC coolant entering the engine, by the time it has flowed around the engine and exited the other side, it will have absorbed heat from the engine and increased in temperature. Let's say it's gained a 8 deg C rise in temperature as it takes heat away from the engine, that now makes the coolant leaving the engine at around 90 degC.

 

The temperature sensors on a K-series are normally located on the water rail where the coolant first exits the block. So in the case above they should read around 90 deg C, if you had a 82 degC thermostat.

 

The 90 Deg C hot coolant now flows around to the radiator and cooling circuit and is eventual returned back to the thermostat or PRRT, having first being cooled down to a temperature of less than 82DegC... and the whole coolant flow cycle starts again.

 

My car has a tuned 1.8k and has a 82 DegC PRRT (standard grey PEL500110 from Land Rover) fitted. My ECU and digital dash both read a very steady 92 Deg C when the engine is fully up to temperature (temp gauge and probe are calibrated and correct). I guess this means on my engine, there is an approx 10 deg C heat delta between inlet and outlet of coolant (if the PRRT is indeed working as claimed at 82 DegC).

 

My query is - In other posts where people are using 82 DegC stats or PRRTs, I've read people saying they get approx 80 deg temperatures at the temp gauge - I just don't see how this can be possible, unless;

 

(a) the thermostat/PRRT is actually opening far earlier than 82Deg C

 

(b) the engine is cooling the coolant rather than heating it up by the laws of physics the coolant leaving the engine has to be warmer than that entering it.

 

Question 1 -What temperatures are people seeing on their K-series and with what thermostats (presuming your temp gauge is accurate) ??

 

Question 2 - Is there such a thing as a PRT or PRRT with a lower temp than 82 DegC? My car has been running fine at 92DegC for a few years now. But if I had the option I'd like to reduce the temperatures by 5 Deg C or so. The lowest land rover PRRT is 82DegC, but I'm guessing someone must make an alternative?

 

Thanks.

 

 

 

[The Headmaster]

This is why I fitted a QED housing and stat on the other side of the engine so that it controls the exit temperature of the water.

 

Never a problem after fitting. I also fitted a 74 deg stat which could be said to be to cold for a K but I liked the margin - I would still see 87deg ish leaving the engine.

[skydragon]

Dad- so you are seeing an approximate 13 Deg C delta between thermostat and coolant leaving the block.

 

I went for a PRRT rather than a in-line thermostat, as it gives a higher coolant flow rate and therefore some significant advantages over a remote thermostat. (I'm not saying a remote stat doesn't work, just that a PRRT is better, at least in theory)

[Mankee]

Does the term "82 degree stat" (for example) actually mean that the stat is FULLY open at 82 degrees but starts opening at a lower, undefined temperature? This and temp gauge/viewing angle error might explain why some people say they get running temps of "about 80 degrees".

 

I've only used my engine with newly fitted 82 degree stat as well as the coolant pipes modification briefly on the rolling road with a dirty great fan, but I'm seeing the same sort of behaviour as you are, i.e. Emerald reading around 90-odd degrees.

[The Headmaster]

Yes seeing that temp delta but remember the stat is before the rad. I have no figures for the temp of the water entering the block/pump.

 

Its likely to be significantly lower. I guess by around the difference you are seeing at your stat so another 10 deg?

 

Whenever I have checked stats in a pan they vary slightly - but they largely begin to open a few degrees before the marked point and complete the opening movement a few deg after but remain open on the way back down for quite a few degrees below the marked figure. The wax does take some time to cool.

[Ivaan]

Arn't there two temps for the PRRT. A grey and a white version. I thought the white version was the 82 deg one?

[skydragon]

According to this page here the grey version is the 82DegC version

[SLR No.77]

Mines the standard K-Series cooling setup with an 82ºC stat .... normally shows 90º on the gauge. Nothing verified for calibration but I'm running a Stack temp gauge with solid state sender.

 

Stu.

[myothercarsa2cv]

I run a grey PRRT, standard CC temp gauge setup, reads ~80C all the time, solid as a rock. If I hadn't managed to test the function of the temp gauge extensively before fitting the PRRT ( ) then you'd be forgiven for thinking it was nailed there

[gundersen]

Im with Stu., std. k-series and under normal operation a rock solid 90 degrees as measured by both the dash sensor and the ECU sensor.

[Graham King]

Skydragon, I run a QED housing with an 82C stat and see a steady 80C (on caterham gauge) at all times when running, I haven't checked on the emerald.

 

However in your original post you say "So in the case of a 82 deg thermostat, or a 82 deg PRRT unit, the coolant entering the engine should be at 82 deg C", this statement isn't true, the coolant will be at least 82C but could be higher. The temp of the coolant entering the engine will be governed by the efficiency of the rad not the thermostat (once it is open). I changed to a radtec for this very reason as my original rad wasn't controlling temps well enough for my liking.

 

I would suggest that your actual water temp is higher than 82C as it enters the engine.

 

Graham.

[skydragon]

With a PRRT the coolant entering the engine should be at approx 82 Deg C - why - because cold coolant is bled and mixed into the bypass loop (the main circuit on a PRRT) when the PRRT thermostat opens up and allows cold coolant from the radiator bottom hose to bleed into and mix with the PRRT bypass loop. The thermostat won't work as a perfect device admittedly, but this should ring roughly true if everything is working as intended. The advantage being a very fast coolant flow rate around the engine as the bypass loop is significantly larger than normal and a stable temperature due to the PRRT bleeding coolant into the bypass loop only when needed. This presumes of course that the radiator will provide a continual source of cool coolant to enable the PRRT to do it's job, but the actual coolant temperature isn't determined by the radiator.

 

On a remote thermostat, I'd have thought the coolant temperature entering the engine would be lower than the thermostat temp, as the coolant temperature entering the engine will be in part cooled and defined by the efficiency of the radiator. The hot coolant coming out of the engine is fed via a narrow bypass pipe back to the engine input and also when the coolant coming out the engine is hot enough to open the thermostat, coolant is then allowed to flow through the top hose of the radiator and back into the engine's input, where it mixes along the way with the bypass loop coolant. I'd have still thought though, that the coolant entering the engine would be 82DegC or lower due to the fact it's been through the radiator. eg. If we presume the coolant exiting the engine is at 86 Deg C and the 82 DegC thermostat is wide open, then the coolant will be flowing through the radiator, which will cool it down.

 

I was going to fit a remote stat originally to my car, but i liked the idea of a PRRT constant temperature system. ie. with a remote stat, when the thermostat opens you then get the contents of the cold radiator fed straight into the engine, something a PRRT should avoid. (in saying that my PRRT system doesn't seem to be behaving as intended right now )

 

[The Headmaster]

Your last statement assumes that the stat opens instantly!

 

They certainly do not open instantly as the wax melts so slowly. I understand the idea of a cold slug of water reaching the engine but in reality I doubt it happens. And you should always ensure there is a large enough hole drilled in the stat to allow some additional flow through there also. I used to have a 4 mm hole.

[skydragon]

Agreed that a thermostat will typically open slowly and close even more slowly, so it isn't a 'perfect' regulation device by any means.

 

My comment wasn't regarding how fast the thermostat opens, but about the difference between how a PRRT and a remote stat works.

 

With a remote stat, when it (slowly) opens it will slowly push cold coolant from the radiator bottom hose up into the engine. On the way up the piping, the cold coolant will mix with the hot coolant from the (relatively slow) small bypass piping. The small bypass piping is necessary to ensure there is enough 'back-pressure' so that coolant will still flow through the thermostat (when open) and through the radiator.

 

With a PRRT the bypass is far larger diameter (x 3?) than with a remote thermostat, so there is a far faster flow of coolant around the engine - and the cold coolant is mixed in the PRRT unit itself. To get around the problem of having a large bypass which might effectively rob the radiator of any flow when the thermostat opens, there is a pressure valve in addition to the thermostat which provides some backpressure when the engine is cold and more backpressure when the engine is hot (and the radiator is needed).

 

So in theory the PRRT should provide a far-faster and more temperature-constant flow of coolant around the engine, which is good.

 

The remote stat solution is in some ways a far easier solution. There are far less pipes involved and it could be made more cheaply than a PRRT. I guess that Land Rover felt a high-flow bypass was the key requirement for the K-series engine when they designed the PRRT?

 

I think one possible advantage of the remote thermostat being located at the exit of the engine, is that I don't think it will be affected by cold radiator temperatures like a PRRT or normal thermostat can be (??) It's seeing the input of the radiator, not the output.

 

 

[Graham King]

Skydragon, you are right about the Remote Stat in it's behaviour. In reality you do get some heat "radiating" back along the bottom hose towards the rad prior to the stat opening, but when it does open you do get a bit of temperature cycling visible on the gauge, so it reaches temp, the stat opens allowing the cold water in the rad to enter the engine which (I am fairly certain) allows the stat to start closing again, in my experience it cycles a couple of times before settling dow and is then very steady.

 

Graham.

 

 

[skydragon]

When you have a remote stat fitted in the top hose, do you still have the old bypass hose fitted between the water rail and the engine coolant input, or is the old bypass hose blanked off at each end (as it is with a PRRT install).

 

ie. Do you have two bypass hoses with a remote thermostat install, or just the single bypass hose, from the remote thermostat housing down to the bottom hose (via the expansion bottle piping)

[SLR No.77]

The K-Series cooling circuit is designed with the thermostat at the point where the coolant enters the block to ensure that "cold" coolant is not allowed to enter, therefore not causing thermal shock. The bypass enables warming coolant to flow around the block whilst the stat is still in it's closed position, and will eventually give a high enough temperature to enable the stat to open as needed.

There are plenty of owners (myself included) who believe a remote stat on the outflow side of the block is a backwards step and the only choices for stat are either the standard setup, or, as modified by Rover, the PRRT.

 

Stu.

[Graham King]

I plumbed my bypass into the 16mm pipe that runs between the expansion tank and the bottom hose submarine. I didn't change anything else so I guess there are in theory 2 bypass circuits but the original one one doesn't have a stat in the flow anymore.

[The Headmaster]

Yes 2 hoses - at least I did.

 

I have been trying to answer your questions above not say which is the better system as I have no experience of the PRRT.

 

You have asked questions to which I present an answer and then your seem to defend the PRRT,

 

I know its your age and you are clearly suffering from withdrawal symptoms from not being able to drive your 7 (sorry - when you "try" to drive your 7 in a straight line keeping it on the tarmac......... etc I could go on but that would be boring 😬) but I'd go back to your old temp sender on the rad for the fan switch and fit a manual override so that if it fails you can simply flick a switch on the dashboard

[skydragon]

Dad - 😬 😬 - I did drive my seven at the weekend, for the first time this year....and this is what caused this whole damn question, when the bloody PRRT wouldn't open cause the bottom of the radiator was stone cold (i knew I should have left it in the garage )

 

I'm not saying a PRRT is better... because mine isn't working as I'd like it to Why won't the damn thing work?

 

I'd go back to your old temp sender on the rad for the fan switch and fit a manual override so that if it fails you can simply flick a switch on the dashboard

sounds like a plan

 

[The Headmaster]

One of the main reasons for changing to the QED is to provide much better access should the stat fail ! 5 min job. Should it fail on a VHPD car with dry sump it has to be the worst job on the car

 

On one occasion I gave up and undid the engine mounts to lift the engine for better access. Yes been there done that!

[CageyH]

Quoting skydragon: 

Dad - 😬 😬 - I did drive my seven at the weekend, for the first time this year....and this is what caused this whole damn question, when the bloody PRRT wouldn't open cause the bottom of the radiator was stone cold (i knew I should have left it in the garage )

 

I'm not saying a PRRT is better... because mine isn't working as I'd like it to Why won't the damn thing work?

 

I'd go back to your old temp sender on the rad for the fan switch and fit a manual override so that if it fails you can simply flick a switch on the dashboard

sounds like a plan

 

Did you get it hot enough for the PRRT to allow water to flow through the rad?

It's not been unkown for them not to be open all the time when running on a cold day, as they don't have to be to maintain a steady coolant temperature.

[CageyH]

Quoting skydragon: 

Question 1 -What temperatures are people seeing on their K-series and with what thermostats (presuming your temp gauge is accurate) ??

 

Question 2 - Is there such a thing as a PRT or PRRT with a lower temp than 82 DegC? My car has been running fine at 92DegC for a few years now. But if I had the option I'd like to reduce the temperatures by 5 Deg C or so. The lowest land rover PRRT is 82DegC, but I'm guessing someone must make an alternative?

 

 

1 - Above 80 and below 90 on my uncalibrated gauge.

2 - Fitting a lower temp stat may not reduce the running temperature, as it will just open earlier, but the temperature will continue to rise to probably around 92 degrees. If it is running fine, why worry?

[skydragon]

Did you get it hot enough for the PRRT to allow water to flow through the rad?

yes....but what I've now realised is that the first time this happens after halting the car (when you've run the car up to temperature, but the radiator is stone cold from the airflow whilst driving) is that the main coolant temperature has to climb to near 100 DegC before the PRRT stat will open and let coolant through the radiator.

 

I hadn't reckoned on the fact that the cold coolant in the radiator and bottom hose (which connects to the PRRT) would cool one side of the stat and raise the point at which the PRRT stat will open, by some 4- 5 degrees.

 

Once coolant has flowed through the radiator once and the cooling fan clicks in, everything is ok and the fan cycles on/off ok, as the bottom of the radiator now never gets cold enough to affect the PRRT stat as it initially does.

 

I don't know whether this will happen quite the same when the weather is warm and the radiator isn't quite as cold.

[CageyH]

I have had no issues with my car running a PRRT in temperatures around -10 to +42 degrees C.

It can take a while to heat up, but settles down nice and stable. Only gets slightly worrying when you hit traffic in high ambient temperatures, but that is more to do with the radiator capacity.