The real cause of injector rattle?

[Piggy]

Yup.
So.
Long thread...confirming what we all knew. HDi's run as they should.

[JTaylor2005]

Also confirming that having got a new thermostat fitted the car actually runs cooler than the opening point quite often (80c) stat opens at 83c so wondering if that would be possibly why people reckon the glow plugs in the coolant pulse on and off whilst cruising.

Also that my injector rattle has significantly decreased having fitted a thermostat that is working and not stuck open or leaking around the loose seal like the previous one must have been. (possible to look into when people say their injectors are really rattly might be a cheap way to quieten them down a bit)

Also I have learned a lot so thanks all haha

[pug306driver]

so  the cooling system heater plugs turn off and on whilst driving, temperature dependant?

Since a gate  stat was fitted some time ago our estate sits at 80 on the gauge for steady driving, i have removed both cooling system heater plug fuses and relays just after xmas and all seems ok, i removed them because the relay socket and relay nearest the heater plugs showed overheating signs, melted plastic, but the other one, furthest from the engine seemed all ok.

sometimes after a run and she is idleing at home she sounds real sweet, and others a little clattery, injectors or egr??

[JTaylor2005]

I have heard that I am not sure though. It seems as though when just cruising these engines don't produce enough heat to actually stay hot. Whether or not that is the case with the glow plugs I'm unsure I have just heard that. I will try and wire up a little light soon to see when they do come on and off etc.

[pug306driver]

That's a good idea, maybe 2, one for each pair of plugs......led so no extra current ( 10 milli amps should not cause a problem ) drawn thru the relays, as said one relay and its connection holes in the double fuse/relay board show signs of overheating as plastic has melted a bit on ours.

[toseland]

coolant preheater is that.. a preheater, its purpose is to bring the running temperature of the engine up nearer running temperature more quickly by artificially heating the coolant directly.

this turns off when the coolant is hot enough, and the engine is sustaining the heat as at this point the normal cooling/heating operation of the engine is more than enough to take over.

With this disconnected it takes 20-25 minutes for my blowers to blow warm air, with it connected it takes ~5 so it makes a massive difference.

I am not sure how long it goes on for, but I don't think it keeps coming on throughout the run

[Ruan]

So I was right all along - your gauge is talking billy bollocks.

HDis are SO thermally efficient, they struggle to maintain temperature when cruising because they're actually spending the vast majority of the energy actually driving the wheels rather than pissing it into the cooling system like other engines do!

The later EGR cooled HDis don't require the coolant heater, however when you disable the EGR, you remove the recovery of heat into the coolant and therefore they struggle again to warm up/stay warm.

[JTaylor2005]

So I was right all along - your gauge is talking billy bollocks.

HDis are SO thermally efficient, they struggle to maintain temperature when cruising because they're actually spending the vast majority of the energy actually driving the wheels rather than pissing it into the cooling system like other engines do!

The later EGR cooled HDis don't require the coolant heater, however when you disable the EGR, you remove the recovery of heat into the coolant and therefore they struggle again to warm up/stay warm.

Ahhh see mine is a very early one that doesn't have the egr cooler at all. Its just a straight bit of pipe with no coolant going through it.

I am wondering if on the early ones the glow plugs in the coolant pulse when it drops at cruising and then go off when you get the engine hot by driving harder etc.

And then on the ones with the egr cooling this isn't needed any more as it uses the heat from the exhaust gasses whilst cruising to keep the water temp up higher.

I have no idea I am just throwing ideas around but I don't think Peugeot would have been happy with their cars running lower than the stat rating as that would hurt their efficiency I would have thought. I am not sure though really.


I read the codes off on mine today using the bluetooth reader I have and it has come up with
P0380 - Glow plug / Heater Circuit A

Now I have only changed the cylinder glow plugs about a year ago and they were bosch ones and were all installed correctly.
I am not sure how fault codes are generated for glow plugs though.

[HDi--Power]

The coolant block is called a reheater, not a preheater and I tested it and it pulses on and off all the time regardless of engine temp. The egr cooler seems to make the biggest difference in warm up times

[JTaylor2005]

There you go then. I am under the impression there is no way that the ECU would know whether they are working correctly or not really as they are an open loop system which is a shame.

And yeah I don't have one of those unfortunately as mine is a very early model it only has a normal pipe with no cooler on it so my car would probably be more reliant on the glow plugs keeping the engine temp nice and warm on low load conditions

[Ruan]

Thing is, diesel engines are SO thermally efficient because of the fact normally they are running in an excess of air and have high compression ratios... The temperature of the coolant is nowhere near as important as it is in a spark ignition engine. The classic rule "hotter = more efficient" doesn't stand true from what I've seen, I'd say there's very much a "sweet spot", but I don't think it'd make near any discernible difference in economy, rather just f*ck up stuff like the viscosity of oil - you're looking at the water temperature purely from a efficiency point of view.

There are FAR greater factors affecting the efficiency of DI diesels rather than coolant temperature, notably commencement of injection angle, which is closely intertwined with emissions. I would agree they need to get up to temperature, however this is more from a lubrication point of view, rather a thermal dynamics point of view. Remember in a DI diesel, the part that contains the combustion and where a lot of the heat will go is the piston... The water cooling system is under very little load, the vast majority of the thermal energy is coming from the oil, since this is what cools the pistons.

Have you ever seen a DI diesel melt a cylinder head before a piston....

Of course, this is my opinion on the matter. Very happy to have a debate.

[JTaylor2005]

Thing is, diesel engines are SO thermally efficient because of the fact normally they are running in an excess of air and have high compression ratios... The temperature of the coolant is nowhere near as important as it is in a spark ignition engine. The classic rule "hotter = more efficient" doesn't stand true from what I've seen, I'd say there's very much a "sweet spot", but I don't think it'd make near any discernible difference in economy, rather just f*ck up stuff like the viscosity of oil - you're looking at the water temperature purely from a efficiency point of view.

There are FAR greater factors affecting the efficiency of DI diesels rather than coolant temperature, notably commencement of injection angle, which is closely intertwined with emissions. I would agree they need to get up to temperature, however this is more from a lubrication point of view, rather a thermal dynamics point of view. Remember in a DI diesel, the part that contains the combustion and where a lot of the heat will go is the piston... The water cooling system is under very little load, the vast majority of the thermal energy is coming from the oil, since this is what cools the pistons.

Have you ever seen a DI diesel melt a cylinder head before a piston....

Of course, this is my opinion on the matter. Very happy to have a debate.

That all sounds very true and reasonable. I have always been under the impression that coolant temperature has a large effect on the actual cylinder wall temperatures. Which would then have an effect on fuel atomization etc rather than it condensing against a cold cylinder wall. But that could be total crap and tbh I would expect it would have to be a large difference in temperature to make a noticable difference.

However thinking of that it would be likely that would be more of an indirect injection system where the head has to be hot to help keep the diesel mist finer rather than on a setup where your injecting at 300 bar through micron sized holes.

[Ruan]

That all sounds very true and reasonable. I have always been under the impression that coolant temperature has a large effect on the actual cylinder wall temperatures. Which would then have an effect on fuel atomization etc rather than it condensing against a cold cylinder wall. But that could be total crap and tbh I would expect it would have to be a large difference in temperature to make a noticable difference.

Where and when is the fuel injected on a DI diesel...

Go take a look at the piston bowl design - that might give you a hint as to why the cylinder wall temperatures aren't of massive consequence, other than being at ~80-83*C.

You've just explained why IDI engines are theoretically a better technology than DI diesel, just the practicalities of losing the heat to the head in a very small chamber are a pain in the arse. Not to mention the fact that IDI can generate better swirl to thoroughly mix the air charge than a DI diesel ever could.

[JTaylor2005]

I have always been impressed with how much MPG the older IDI engines actually get though tbf. Side by side there really doesn't seem to be much in it between them a lot of the time.

I have seen the piston bowl design as well. I suppose it just sprays straight into the piston bowl rather than just generally into the cylinder.

[MY95]

So, rather than starting a new thread on the same subject, would you get any more mpg/performance running a 306 hdi with the 90 degree thermostat than the 83 degree standard one? Mine also needs changed as usually sits around the middle 70s, but will creep up to 80-83 quite easily!

[Ruan]

Basically read above.

Check what temperature it's ACTUALLY running at, the dash talks bollocks.

[Paul_13]

^agreed!