Rover L-series diesel questions

Well I took things a bit further today and found some of the answers myself...

The rad top hose will get hot due to thermal conduction as there is no thermostat in the top hose circuit. The gauge reading may be related to a duff temp. sensor as the plastic inner of the sensor rotates within the metal outer (which is threaded and bolts into the head outlet elbow) and I don't think it should.

Thermostat was shut when I removed it and as the car doesn't overheat I assume it is working.

The cylinder thingy IS the thermostat and housing and is fitted in the radiator return pipe. The tee from the top hose is to allow hot coolant to one side of the thermostat to actuate it. The thermostat housing actually has three connections: one on one side (goes to rad bottom hose, via oil cooler), and two on the other side arranged in a Y formation. The straight one of these goes to the rad top hose, and the angled one goes to the water pump inlet.

Hopefully the above might help someone else working on these engines.

Darren

Also sprach "Darren Jarvis" :-

Convection, Shirley?

Have now drained, flushed and refilled the cooling system but the above problem still exists. Here's some more detail (sounds very much like the recent problem with the pinto Sierra a few posts back):

Start the car up and it eventually starts to get warm. By this I mean that the heater feed pipe and the radiator top hose both get warm (not hot, just warm), however the radiator core itself doesn't get warm - the gauge is now starting to move and settles just on the bottom of the white scale (about a quarter) after a few minutes idling.

If I leave the engine idling the gauge doesn't seem to move much above the beginning of the scale, though if I hold the engine at about 2000rpm it slowly climbs to about the half-way mark (which is where I'd expect it be) and goes no further. The fans also do not run. If I take the car for a steady run (50-60mph single carriageway A roads), the gauge slowly goes down, sometimes off the bottom of the white scale altogether! Stopping and lifting the bonnet when this is case, the rad top hose is only lukewarm, as is the radiator core and output from the heater.

Tonight I put a big bit of cardboard in front of the radiator (had to remove the top mountings to do it) which covers the entire core and intercooler, though there is about an inch gap between the card and the radiator. Driving home 'energetically' I expected the gauge to climb over the half-way mark but it just sat there, again, even with the car stationary and the engine revving. Fans still don't run, but do if you disconnect one of the radiator switches and short the wires together.

I took the thermostat unit off this morning and held it under the cold tap - it was firmly shut, though I wasn't able to check what temperature it opens at.

Any ideas? It's sounding like a thermostat opening far too early (not replaceable on it's own, it's part of the plastic cylinder housing), or maybe the cooling system is plumbed in backwards???!

Darren

Maybe its just a case of the sensor circuit gauge is defective and the cooling circuit is doing what it is supposed to do. Are you sure the water pump is doing what it is supposed to do? Being a thermal engine it is difficult to know if the pump is OK.

Give you an example. Got stuck in a jam yesterday between junctions 9 and

10 on theA27 as two wallys decided to have a coming together. The gauge took ages from the moment I started moving to a point just before we stopped for the accident as it was near to 0 degrees outside. From then, stuck in the jam the gauge did not move upwards from its normal moving operating point but actually fell slightly. The fan did not cut in at all.

You have to remember that a diesel engine is a thermal engine, under correct operation the temp will rise to a given point and stay there. You say you tested the thermostat, but running it under cold water does not do this. You need to suspend it in a saucepan of water on the cooker and slowly increase the water heat until it can be seen to open. A thermometer in the water will give you the correct readings.

If you are that worried, change the thermostat. If you still have the same fault, start looking elsewhere, look at the gauge system or the water pump.

PDH

From what I've read here and elsewhere, most people with the same engine experience the gauge settling around the half-way mark. Mine doesn't get anywhere near that during normal driving, and frequently doesn't even reach the bottom of the scale! I could live with it if it was just an inaccurate reading, but with the radiator top hose not even getting that hot I think there is something more seriously wrong.

After blocking the rad with cardboard last night, the gauge stayed at the half-way mark whether driving or idling. It also made an improvement to the performance, and I suspect the fuel economy (at the moment I'm only averaging about 38-40mpg which is rather poor), as well as having the benefit of hot air out of the heater rather than merely warmed air.

I do suspect the thermostat, but I've never previously seen one that closes fine but opens too early. Not only that, they're not cheap (parts factors don't list them) and I've just added a tenner's worth of new anti-freeze to the system during the refill. If I could find a s/h engine in the scrapyard though...

Darren

I've just changed one that did that :-)

That's how they usually fail IME.

Chris.

The economy would go right out the window if the thermostat was opening too early as the ECU would be getting confused by the cool water readings (it thinks its still cold and will advance the engine to compensate). It's possible, I havn't personally had one thats gone futt, I'm usually unlucky to have something more serious go kaput.

Yup, go for it, fit a replacement.

PDH

Looks like it's the most likely culprit so I'll just have to buy one and see. Anybody know how much a Rover dealer would charge for one (tried my main parts supplier but they don't even list it so I'd appreciate if anyone knows otherwise).

Thanks for the suggestions, I'll try it as soon as I can get one and I'll report back. At the moment the cardboard blocking the rad is doing fine!

Darren

Went down the M42 today and noticed that the gauge had climbed higher than the half-way mark so I pulled over at the next services. Sure enough, both fans were running (only slowly though) so I'm relieved that they work. Stripped off about 6" of the side of the cardboard piece to expose the intercooler and part of the radiator and continued to South Wales with no further problems and the gauge at the half-way mark exactly as it should be.

Darre

Well I bought one yesterday (about £26) and fitted it this afternoon. Car now warms up to normal temperature fine (though still very slowly) and stays at the half-way mark without budging.

Just for a laugh (sort of) I hacksawed the old thermostat housing apart and extracted the rather large thermostat inside. I tested it in a saucpan of hot water and observed it opening and closing normally! However, the temperature rating stamped on the rim was 35C - what the heck would use that low a temperature?!

Needless to say, I've now removed the cardboard from the front of the rad and the car is behaving itself. Hopefully it'll also do much more mpg...

Darren

That sounds a lot better. The slow rise is normal but you will find the economy getting better as the ECU gets to re-learn the car characteristics. Check your header over the next few days just in case you have any residual air in the system.

One gets the feeling that you may have had a petrol engine type thermostat fitted instead of the correct unit. The valve may have to open early due to the sudden temp rise of a petrol engine, especially if it was a valve for a

1.8 K engine.

I think you will now have little trouble at all from now on with the way the car operates. I have found that under normal cold weather conditions the engine takes ages to warm up, so if you get a cold snap, wherever you are, don't panic.

PDH

I thought that might be the case so I disconnected the battery for a few minutes (also gave me chance to clean the terminals, etc.) to force it to re-learn. That's assuming it is a learning processor (like fitted to Terminator!).

K-series engine have a seperately replaceable thermostat on the back of the engine near the inlet manifold, so it's unlikely that the old one was for that, but it was almost certainly for a Rover as it is identical in every way apart from temperature rating...

Hope not! One of the main reasons for buying it was the improved fuel economy over the 1.8 Peugeot diesel fitted to my previous 418, so I was less than happy during my first week to find it doing worse than 40mpg. Also not keen on the low, laid back front seats - they'll be getting replaced before long with something I can adjust the height on (or at least the bottom cushion angle).

Darren

Thought I'd share what I've learnt in case it helps anyone else...

The thermostat has three connections; an inlet and an (angled) outlet on one side, and an inlet on the other. The angled connection goes to the water pump, the inlet on the same side connects to the top hose tee and the remaining inlet on the opposite side connects to the oil cooler outlet (which is connected to the bottom hose of the radiator).

The thermostat itself selects one of the two inlets to pass coolant to the angled outlet. With the thermostat closed (cold), coolant is admitted from the cylinder head outlet, via the top hose and tee, through the thermostat housing and out to the water pump where it agains enters the engine block. No coolant flows through the radiator and oil cooler as it's outlet is obstructed by the closed thermostat.

The inlet from the top hose is designed to flow coolant around the wax capsule in the thermostat before passing out to the pump - this way the thermostat is heated by the coolant to a temperature close to that of the cylinder head outlet. When the thermostat starts to operate, it open the inlet from the oil cooler, and presses a disc against the inlet from the top hose. Now coolant is blocked from flowing down the tee from the top hose and is instead directed through the radiator. The disc which blocks the top hose inlet is spring loaded to allow the thermostat to continue opening after it has contacted the seat inside the housing.

As the coolant is cooled by the radiator, the thermostat closes to stop flow through the radiator, and uncovers the inlet from the top hose again, thus bypassing the radiator until the coolant reaches sufficient temperature to open the thermostat again.

Darren

I can always tell if the wife has been driving the car as it feels different until I have driven it for around half an hour. Talking to a Rover tech a few years ago I was told that the ECU monitors things like the accelerator, brake pedel (how heavy you are and at what rate you take power), gear changes, plus the internal sensing electronics for how the car behaves while you are behind the wheel. I'm notoriously heavy on the pedal and the car drives accordingly, while the wife moans that the car behaves like a dog for the first half hour until it realised the driver is being kinder on the controls. I managed to prove this when I came back from a long holiday and the car, which had only been driven a few hundred yards in the pound, behaved as I left it.

Might have been from some other rover diesel, maybe a Maestro engine, who knows. The linage of the L series diesel goes back quite a way so its possible that older spares may fit. Maybe somebody else can advise on this matter as I tend to specialise on the engine I'm driving.

Anything is better than a pug engine, trust me. Do you do a lot of long runs to work etc.? On a full tank, with my heavy boot, I tend to get around 440 miles on 11 gallons of diesel. Remember the Labour induced fuel crisis a few years back? when I was driving during that and pussyfooting around, trying to eek out a tank of fuel, I was getting near on 700 miles on a full tank load. It is possible to get some startling economies on an L series engine, modern diesels are even better, but you have to be really light footed to squeeze it out.

As for me, I just like the grunt! :o)

Also of note, the seats in a Rover are one of the very few that don't give me a bad back on long distance travelling (like a recent Brighton to Grimsby trip with just one stop outside Sheffield). Horses for courses I guess.

PDH