Hi again !! I am a bit puzzled or, more correctly, a bit concerned about a loss of coolant from the P38. I have a feeling that I know what it is but I am hoping that someone, who has experienced it, might be able to sort of confirm my suspicion.

Now that the weather has got a bit cooler I have had the heaters on warm or hot, to give a bit of extra warmth in the vehicle. I have noticed that the coolant is now disappearing at about a quarter of a pint over a 50 mile shopping/going for coffee journey. This is in comparison to a journey to Scotland, two months ago, which was about 600 miles in total and didn't use any coolant.

So, basically, there didn't seem to be coolant loss when the heaters are not used, but now that they are used the coolant is disappearing.

The issue seems to only be on short, multiple journeys, and seemingly when the heaters are used. I strongly suspect that the carpet is a bit damp under the heater unit, inside the vehicle, and I am wondering if this could be caused by the famous rubber seals on the heater pipes from the engine into the cabin leaking ?

Pierre3.

It shouldn't make any difference whether the HEVAC is on hot or cold because that's just the flap positions. The coolant flows through the heater all year round. More likely you have developed a leak somewhere.

Interesting information. Is there any reason why there would be coolant on the ground just behind the drivers' side front wheel ? If one didn't know otherwise one would think that coolant has dropped straight out of the bottom of the reservoir onto the ground, which of course it can't. I had a look into the body cavity beside the reservoir and it is all dry, from what I can see.

The coolant on the ground is kind of where the sunroof drain would possibly drain out, and there is nothing behind the front passenger side wheel. I can't see any reason for coolant to leak onto the ground right behind the wheel, so I don't know where it is coming from.

Pierre3.

scuttle probably drains out in that area too.?

To check for a matrix leak, get a couple sheets of kitchen roll and slide them in between the underside of the heater box, and the carpet. If its leaking you'll soon see the paper get wet.

FWIW, my slightly broken engine used more coolant on short trips than long ones. I can drive 100miles continuously without needing to top up, but a few trips back and forth to the nursery would see the tank empty. Not got enough data after the head gaskets to see how that has changed.

The overflow from the coolant reservoir drips down behind the RH front wheel. If you have filled to the upper mark and the pressure cap has reached its sell by date, it will be pushing some out of the overflow. Have a look below the reservoir and you may see damp down there.

I second Richard straight.
I had the same puzzling issue years ago, until I made a longer pipe/hose from the overflow to a small bottle wedged down there by the firewall.
Some testing showed my RV8 does not "like" coolant to be at its cold level mark, it will sooner or later spit it out.
Usually on short journeys, while on long, even at high speed and loaded, where I would expect higher "drinking", it doesn't.

I removed the contraption, and I now fill the reservoir 2/3 of the mark. I haven't had a overflow spill since ... at least 20k km so far.
Every few days, I pour a small quantity when level reaches half of the reservoir, to 2/3 as said. No overheating, not an issue. And heater works and pumps heat in abundance. I learned to live with this 'quirkiness' ...

Hi, thanks a lot for the very useful information.

So, a couple of things - I think that I might buy a new pressure cap as I don't know how old mine is. But it certainly explains the coolant on the ground behind the front wheel, so thanks to Richard for that information.

Aragorn - I have a new seat base that I am fitting to the drivers' front seat [well, it wouldn't be the drivers' rear seat, would it - dohhh], so I took out the seat today, and that gave me a better look at the carpet under the heater, and guess what - I can see coolant on the transmission tunnel carpet just above the footrest. So I am pretty sure that [a] the heater matrix is leaking, or the seals into it are, and [b] I need a new pressure cap.

I am 98% certain that the engine is sound, it's a diesel by the way, as there hasn't been any noticeable change in performance. Not a guarantee, I know, but there is no white smoke anywhere, the oil level hasn't changed, and the exhaust is nice and clean. I did fit a new water pump and thermostat last Autumn, and I fitted a new Direnza radiator about three months ago. My water temperature sits steadily at dead centre and never goes up above that. When I first got the vehicle 5 years ago the temperature never went above the blue section, which I thought was correct, even though there were mentions on the internet that this is a problem, and not a good thing. Then my water pump broke the end off !!

Leolito, I understand how your issue worked, but mine is definitely using or loosing the coolant. Definitely leaking into the cabin, so along with a weak pressure cap I can understand where all the coolant is going.

The biggest issue now is fixing the leaking matrix seals, if that is the problem. I could also do with sorting the blend motors which I think are a bit iffy, and [does this ever stop] I think that the passenger side heater fan may have stopped working. About 18 months ago it started making a noise as if a big leaf was stuck in the fan blades but it would stop if I switched the fans on and off a couple of times. But it would sometimes come back unexpectedly.

Pierre3.

If you have never changed the heater core O rings since you have had the car, they will likely need doing. Despite what you may have heard, it is a relatively simple job, just a bit fiddly. The last time we had a P38 summer camp, I did 3 sets in as many hours.

Easy to tell if the heater blowers are working, just take the pollen filters out and have a look down the hole. If you see a stationary fan, it isn't working.

Genuine Febi cap can be got from Amazon of all places, see https://www.amazon.co.uk/gp/product/B0068M7JNA/

Thanks Richard. Great advice, I will have a look inside the pollen filters tomorrow.

Pierre3.

check your water pump if you are using a little bit of coolant. there is a hole under the pump that will tell you its leaking . the hidden water leak.

After doing a job on the handbrake I am 99% sure that the heater O-rings are leaking. I can see an orange reflection from the carpet when I shine my large garage light into the footwell. As well as that the carpet under the heater foot vent, on top of the transmission tunnel, is wet. Hopefully, there isn't too much being absorbed into the carpet, although there is some for sure.

Pierre3.

Something that makes me wonder about leaking O-rings - if the car is just sitting parked does the coolant still leak from the heater O-rings, into the carpet below ?

I still have not decided what to do about repairing said O-rings but I am not driving the car for the moment as I don't want to escalate the problem of the coolant soaking into the carpet. I know a few people have suggested that taking out the dashboard is not particularly difficult but I am not sure that I want to tackle it myself. If I do decide to do it myself then I will have to wait until the spring when warmer weather will return, but I don't want the coolant to leak out into the car in the intervening months.

Something else that occurs to mind - how is the best way to dry out the coolant from the carpet. I was thinking of putting a small dehumidifier inside the car but I don't like the thought of closing the door with an extension lead hanging out, in case either the cable gets damaged or the gap in the door and frame gets moved. Maybe someone has another solution ?

Pierre3.

It will still leak but not as much as when it is being run as the coolant won't be under pressure. Get a bit of kitchen foil and make yourself something for it to drip onto rather than the carpet.

My gems 4.6 seems to only lose coolant when heater is in on. It only drops 1.5 inches in the header tank, then stops leaking. Damp sweet smelling carpet - assumed it's matrix o-rings (or matrix), bigger problems today.

It shouldn't make a difference if the heater is on, it is a full flow system so the coolant will be flowing through it whether on or not.

Kbs - my own vehicle was doing something similar for a while, but it appears more pronounced now. A couple of short runs, say 20 miles, and the coolant is at the bottom of the expansion tank.

Richard, I had indeed wondered whether the coolant circulated all the time. I thought that to be the case if only because, in years gone by, on way to help cool a hot engine was to put the heaters on full in an effort to reduce temperature. But - I had sort of hoped that, for some unknown [!!!] reason, the coolant wouldn't circulate if the heaters were left on cold.

Pierre3.

The only way to stop it circulating is to link the two pipes that come from the engine to the heater matrix pipes at the bulkhead so nothing flows through the heater.

Hi pierre3. I've been lucky and never lost more than a little, excluding a hose failure that I mistook for a water pump leak:)

Hi Gilbertd, maybe my leaks were caused by cooling the hot matrix with the cabin fans? I think my old polo has a valve in the matrix feed - cant think of others I have seen in person.

Years ago all cars had a tap that was operated by the hot, cold or somewhere in between knob or slider which simply regulated (not very well in most cases) the flow of coolant through the heater matrix. For the last 20 years or more, nearly all cars use a full flow system where the temperature is regulated by altering the amount of air that goes either through or around the matrix. That way blend motors can be used to constantly adjust the temperature electronically. In my fleet, as well as the P38s, I've got an early 80's car that uses the tap method and that is pathetic as you can never shut the flow off completely so no matter how hot the weather is so it is windows and sunroof open all the time. Then I've got one from the early 90's that uses a sort of half and half where it has a tap but adjusted by a little electric motor with feedback to tell the controller what position it thinks it is in (mostly, but it is Italian and we all joke about Joe Lucas the Prince of Darkness but I think he was taught everything he knows by the Italians....).

I've had 80's cars that used full flow heater matrices and a mechanical blend door. Seemed to be a bit of a mixture back then, but everything has gone that way now. Engines need coolant flow even when the thermostat is shut. Everyone eventually realised that pumping it thru the matrix was the easiest way to achieve this and keeps the coolant circuit nice and simple.

I've run a dehumidifier in mine quite a bit, the cable just squishes into the seal if you place it carefully at a corner. Part of the problem though is coolant doesnt evaporate very readily at low temperatures, which you'll notice if you spill some on the garage floor. Which means extracting it with a dehumidifier will probably take eons.