Cooling/heating bit of guidance
Hi all
The heater my 300GD (1985) has decided to stop heating. Now I know a reasonable amount about how it all works so am looking for a bit of guidance to trouble shoot it.
Points are as follows
1 all the levers are connected and working
2. There is some heat transfer via the heater matrix, but increasing the fan speed simply reduces the warmth to the point you are putting exterior temp air into the car
3. The coolant level is good - a minor hose weep was sorted a few weeks ago
4. The heater arm for temp control is moving the lever correctly on the valve that allows flow through the matrix
5. As far as I can tell the water pump is working - it is worth noting that even on a prolonged full speed run the temp never gets to the mid temp mark (not unusual I believe) and on stopping you can remove the radiator cap with no problem (I know there are meant to be issues with the removing that rad cap on hot pressurised systems, but not sure if that applies here - legendary cool running 300GD similar to land Rover Discover??)
5. With ref 4 to the above you can do this with the engine running, no probs
6. I have checked the hoses and on a short ish run I.e enough to bring the temp up to just past the first mark, with the heater full open and fan on low speed the return hose from the matrix was cool/cold. On a previous long run of 1 hour all hoses were warm - but then again so is all the engine bay
All lot of detail I realise. So my question is is peoples experience would the suspect be the valve that is actuated by the heater lever - in which case it must have failed shut! Despite the lever moving. Could it be a blockage - the heat matrix was replaced 6 years ago and has no leaks, the carpets are dry etc. could it be the water pump and the reason why it does not overheat is because the convection effect produced enoug water movement to keep the engine cool in our now typical English spring, or could the rad cap itself be playing a part as my expansion drain off is simply a hose from the rad neck. Again I am assuming the rad cap on the G does act as a fail safe pressure relief valve and if it does, may have failed open?
All thoughts greatfully recieved - it's not the warmest of car, but I would have expected to have a Luke warm interior at the current air temps!
Many thanks
Simon
Hello simon666,
I would firstly replace the thermostat, even on diesels, the coolant temeprature should rise upto the operating temperature at approximately 85 degrees celceius.
Check, the inlet hose to the matrix, compare the hose temperature with the outlet side, if these are almost equally warm; the heater matrix is OK, otherwise, you could have a blocked heater marix. If so, disconnect the two hose at the matrix and hook up some pipe work to flush the matrix out, if you can, using some flushing agents to assist if possible. Then, after the cleaning, hook your hose up from the engine and check the workings again. Ohh, if the inlet is warm or hot, and this temperature is not the same after the heater control valve, then it is the heater valve that is failed in the closed position and it is not then the blocked matrix. So, check the valve first, then clean the matrix.
Cheers,
Hello Simon,
If the water pump was not wroking, you would get a quick build up of heat in the block and the radiator may be stone cold. You would know, because the vehicle would start overheating.
You say there is a small trickle of water flowing at the disconnected heater matrix hose, this suggests to me that there is some sort of restriction here, which will need investigation.
I would do your long run firstly, and depending on the results you get from that, will dictate your next move.
It could be the temperature gauge is reading wrongly, to test that, earth out the temperautre sender unit and the temperature gauge should read hot. I will have to check and come back to you, with how to locate the temperature sender unit, I can not remember which it is.
When you start your engine from cold, check the top radiator hose after the theromastat and take a mental note on the temperature by hand - obviously cold. About five to ten minutes into your journey, safely park up and take another feeling of temperature from the same point after the thermostat. It may start getting warmer, do another five to ten minutes drive and do another check, the hose should be getting warmer still, do the same at the heater matrix inlet hose to check the temperature feeling.
I have to double check, but I am wondering if the heater matrix hoses could be mixed up, if wrongly fitted, this could affect the heat at the matrix, in fact this may even explain the trickling of water as you had, when you disconected the hose? I will check and come back. I am assuming you have the OM617 engine, five cylinder.
Carrying on, after your long run, switch off the engine, carefully feel the surface of the radiator this should be evenly tempered, there should be no cold spots and hot spots, which indicate blocked radiator, but that is not your complaint any way, your radiator is not hotting up, or not quickly enough, and this suggests the thermostat.
Cheers,
Hi Rakesh
First reasonable run since the flush and valve clean and the heating is very much improved i.e produces hot air which cools with increased fan speed, but still stays warm, so perhaps there was some form of blockage/airlock. Strange given all the parts have been replaced within the last 6 years i.e. engine inc pump, heater matrix and rad, and the servicing is now comprehensive - but you can't argue with the facts.
However the car still take an age to come up to temp - sits to the left of the mid mark at it highest on long runs, and will push past the mark occasionally on hot days or for very brief high load, low speed bits, so I think I will get the thermostat replaced soon.
Many thanks again
Ta
Simon
yeah of course agree with you all guys and I am very grateful with these guidelines here. I know for sure that i can do the same thing just like that. I agree with this the first one ' all the levers are connected and working"
Thanks,
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Hi Rakesh
Many thanks for the reply. Understand about the thermostat and I suspect it might be at fault even though it was replaced with the engine 2 years ago.
I have flushed the matrix and removed, cleaned and reset the inlet valve - after checking it works. I will have to wait til I give it a long run to check operation as 10 mins on the drive with me holding the viscous fan coupling still - it spins no matter how cold the engine, but has very little resistance when you grab hold of it - did not get the car to the first temp point.
Thats said whilst the temp does not get up quickly, I am pretty sure the thermostat is not stuck open. I started the car with the hose off the heater valve on the inlet side and only got a trickle of water out, so I guess this means either the thermostat is not allowing water flow (as it should be when cold) or the pump is not working - but as I said given all this was done when cold it is a bit hard to tell, well at least with my limited knowledge of how each bit of the cooling system works on the G.
Many thanks for you advice, and this is just an update as I had 30 mins to look at this morning - hence why I checked the simple bits first.
ta
Simon