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VW Golf mk4 TDI PD serious fuel leak, fuel in coolant

birolacoo

Standard Member
Hi,
So, I have a 2001 VW Golf mk4 with a 1.9 TDI PD (AJM or AJR not sure, can check) 115 bhp thingy which used to be a car.

As I mentioned in the title, there's fuel in the coolant currently and I had a very bad fuel leak as well. I haven't switched the engine on for more than a week now due to this.

The mechanic I called over to check the car couldn't find the leak with the engine switched off and it wouldn't start. Later on I started it up, and within the first minute the coolant reservoir was overflowing due to the huge pressure and started to leak.

- EDIT
This was NOT a minor leak, but within about the ten minutes while the engine was running I lost almost a quarter of a tank of fuel.
-EDIT

The mechanic never saw the issue earlier, so he told me to try to research. So I asked around and so far the most likely explanation seems to be a broken cylinder head.

I'm really unhappy with that as the car's value does not really meet the required cost I would need to invest in having it changed.

I tried to research it but I couldn't find anything particularly relevant.

You can probably tell that all I know about cars is limited to what we learned about internal combustion engines in Physics class 25+ years ago.

Please, please, please, give me a lead on this. So I could pass it on to a mechanic to get it sorted.

Thanks a lot!
 
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Delvey

Distinguished Member
If your car is losing a quarter of a tank of fuel in such a small space of time, and it is coming through the head gasket, it will also likely be in the oil. As will water. Check the oil through the filler cap and dip stick for any white residue. This usually means water in the oil.
However, I doubt fuel leaking through the head gasket would go though quarter of a tank. This will be a high pressure fuel leak, likely a fuel injection or fuel pump
 

birolacoo

Standard Member
If your car is losing a quarter of a tank of fuel in such a small space of time, and it is coming through the head gasket, it will also likely be in the oil. As will water. Check the oil through the filler cap and dip stick for any white residue. This usually means water in the oil.
However, I doubt fuel leaking through the head gasket would go though quarter of a tank. This will be a high pressure fuel leak, likely a fuel injection or fuel pump
We checked the filler cap and the dip stick and so had the mechanic for white residue. That's why we ruled out the head gasket l, which would should been a cheaper fix than the cylinder head.

I also found other options as the tandem pump or injector cups, but those don't explain the fuel in the coolant. Well. Not to me at least.

(It's not just a layer on top of the coolant but basically that's all there is in the reservoir).
 

mjn

Distinguished Member
Have you asked the Golf Mk4 forum?
 
Aren't mechanics supposed to troubleshoot? Or do they just literally fix what you tell them to fix?
Indeed, I'm probably missing something but it feels a bit like getting a dog and then barking yourself.

I'd use a different mechanic, garage.

Losing a quarter tank (15 litres?) of diesel so quickly (10 minutes) and ending up in the expansion tank immediately sounds very weird, and costly. Considering it is a 2001 car and worth no more than £1,000 I think that unless you can find another engine cheap and you know how to swap it, that it is just uneconomical to get fixed if you have to pay someone else.
 

Delvey

Distinguished Member
That's why we ruled out the head gasket l, which would should been a cheaper fix than the cylinder head.
I am not sure how a cylinder head would fail. It is just a block of metal. The mechanic does seem clueless as well. Even with a fault cylinder head, I cannot see you losing so much fuel. As mentioned, a quarter of a tank is around 15 litres, and the coolant system only holds 8 or so litres (I recently changed the temp sensor as the seal had failed on the same engine, and it took just shy of 7 litres to refill).
 

birolacoo

Standard Member
Aren't mechanics supposed to troubleshoot? Or do they just literally fix what you tell them to fix?
Because he couldn't find the issue, he said he'd rather not start it on the roadside and suggested me to research.
Indeed, I'm probably missing something but it feels a bit like getting a dog and then barking yourself.

I'd use a different mechanic, garage.

Losing a quarter tank (15 litres?) of diesel so quickly (10 minutes) and ending up in the expansion tank immediately sounds very weird, and costly. Considering it is a 2001 car and worth no more than £1,000 I think that unless you can find another engine cheap and you know how to swap it, that it is just uneconomical to get fixed if you have to pay someone else.
That's what I really did not want to hear. I bought the car less than a half a year ago for £800. And now a huge amount for a major repair... We'll see. I have a promising lead from a mechanic, I'm hoping.
 

birolacoo

Standard Member
I am not sure how a cylinder head would fail. It is just a block of metal. The mechanic does seem clueless as well. Even with a fault cylinder head, I cannot see you losing so much fuel. As mentioned, a quarter of a tank is around 15 litres, and the coolant system only holds 8 or so litres (I recently changed the temp sensor as the seal had failed on the same engine, and it took just shy of 7 litres to refill).
All that fuel ends up on the ground. We realized the leak on the last trip with her all under the car. On the spot we couldn't check for anything. I asked my housemate to drive the car home before all the fuel runs out and took my daughter from school by bus.

The next day was, when the mechanic came being unable to start up the engine even with easy start. Than later on I tortured her until it started up. He was there in 2 minutes, when the leak started again. All through the expansion tank. No leaks anywhere else were seen.

It may have been much less than a 1/4 of a tank, but definitely way more than 5 litres. Pouring under the car. I'm not sure about the fuel gauge either.

Before it started it was above the line over half and after it was around the line just under half. May have only been a fifth of a tank.
 

noiseboy72

Distinguished Member
OK, so my first question is actually is it fuel in the coolant? Does it smell / look like diesel or is it the red coloured coolant?

This sounds much more like a coolant system issue and it's not diesel that's ending up in there, but excess coolant due to a blockage or head issue.

I cannot think of anywhere in the engine where high pressure fuel in any quantity could get anywhere near the coolant system, unless there's a split injector AND issue with the head. The fuel pump, pipework and injectors are all external to the engine, with only the injector running down into the block. I would expect a leak to end up with fuel being leaked onto the ground and not into the coolant system.
 
Agreed. If it is “just” a fuel leak it doesn’t have to be that expensive to fix. And could also explain why the car was very difficult to start; for example lack of pressure for the injectors. For it to make its way into the coolant system in quantity I would find surprising.
 

birolacoo

Standard Member
OK, so my first question is actually is it fuel in the coolant? Does it smell / look like diesel or is it the red coloured coolant?

This sounds much more like a coolant system issue and it's not diesel that's ending up in there, but excess coolant due to a blockage or head issue.

I cannot think of anywhere in the engine where high pressure fuel in any quantity could get anywhere near the coolant system, unless there's a split injector AND issue with the head. The fuel pump, pipework and injectors are all external to the engine, with only the injector running down into the block. I would expect a leak to end up with fuel being leaked onto the ground and not into the coolant system.
When we were establishing what is actually happening, we sort of ruled out the cooling system issue, as the engine was not at all overheating. Reached the 90 degrees and stayed there beforehand. The reason we wanted to eliminate it, because just before the leak happened the first time (when driving to the school to pick my daughter up), the check coolant message came up. There was enough in there, but I added a little more...

//-
Here I have to mention, that I was not using red coolant, but whatever antifreeze I found, just to make sure I had something in the car in case I'd need it
-//

...Than I drove the car for about 15-20 minutes. The warm up time seemed completely normal. And it did stay there. My friend and I were constantly checking it. Even when he drove it home with the gigantic leak it didn't go over 90 degrees.

We figured (later) that the check coolant message must have came up because of the diesel in the coolant as it would change it's conductivity making it seem low to the sensor. We may have been completely wrong.

***
EDIT/UPDATE
Yes, it does smell and look and smell like diesel. Just yesterday I opened the bonnet, thinking we must have been stupid and it must be oil and the diesel leak is coming from elsewhere, so I opened the reservoir, put stuck my finger in the blueish liquid and it smellt like diesel.
 

noiseboy72

Distinguished Member
Have you checked the oil level? Has this increased due to fuel contamination?

Poor starting and a fuel leak could be fuel pump - about £75 untested off Ebay, but this would not explain the fuel in the coolant issue.
 

birolacoo

Standard Member
Have you checked the oil level? Has this increased due to fuel contamination?

Poor starting and a fuel leak could be fuel pump - about £75 untested off Ebay, but this would not explain the fuel in the coolant issue.
The "funny" thing is, that through the five months I had the car we checked the oil level basically every month. There was absolutely no change. Just before this happened it was checked as well and so was after it. The oil level was the same just as the viscosity of it.

Regarding the poor starting the mechanic said there was loads of air in the system which made it a hard-hard start.
 
I may be a little confused, but I thought (especially on older cars like a 2001) you can’t just put anything in as coolant and definitely not mix it.
 

birolacoo

Standard Member
I may be a little confused, but I thought (especially on older cars like a 2001) you can’t just put anything in as coolant and definitely not mix it.
This is why I tried to make sure everyone knows I have no idea about it by saying:
'You can probably tell that all I know about cars is limited to what we learned about internal combustion engines in Physics class 25+ years ago.'
That is my mistake. I did not know. My friend checked what temperature it would freeze at and we bought the "appropriate" one.
 

Delvey

Distinguished Member
I may be a little confused, but I thought (especially on older cars like a 2001) you can’t just put anything in as coolant and definitely not mix it.
Bl4ckGryph0n is correct. The recommended coolant is G12. Normally a pinkish red cooler. As for the coolant smelling like diesel, diesel doesn't really have a smell. Petrol does, and a petrol leak you can smell a mile off (having replaced the fuel filter on a petrol Mk5 golf, which the fuel line was not correctly fitted the smell of petrol was overwhelming immediately, and I have a poor sense of smell).
 

nvingo

Well-known Member
So could the tainted smell and poor starting be due to the mixed coolants?
There can't be 'much' difference in what the coolants do, but compatibility with the materials constituting the engine block, seals, hoses, radiators and pump impeller, and the engine's designed running temperature, are probably what determine the different formulations.
A single coolant type, used for a limited duration in an emergency and subsequently flushed and replaced with the specified type, shouldn't cause long-lasting damage?
Mixed formulations could create undesired chemical reactions?
If the engine is hard to start, is working hard to produce sufficient power to move the car, would use more fuel, run inefficiently/uneconomically, result in more rapid moving of the fuel level gauge?

For the coolant level to drop and illuminate the lamp, would indicate coolant loss via a leak; remember coolant expands and contracts with engine temperature and should only be checked and topped up at the recommended temperate (I guess 'cold'?) and the reservoir is also known as an 'expansion tank' for that reason.
 

birolacoo

Standard Member
So could the tainted smell and poor starting be due to the mixed coolants?
There can't be 'much' difference in what the coolants do, but compatibility with the materials constituting the engine block, seals, hoses, radiators and pump impeller, and the engine's designed running temperature, are probably what determine the different formulations.
A single coolant type, used for a limited duration in an emergency and subsequently flushed and replaced with the specified type, shouldn't cause long-lasting damage?
Mixed formulations could create undesired chemical reactions?
If the engine is hard to start, is working hard to produce sufficient power to move the car, would use more fuel, run inefficiently/uneconomically, result in more rapid moving of the fuel level gauge?

For the coolant level to drop and illuminate the lamp, would indicate coolant loss via a leak; remember coolant expands and contracts with engine temperature and should only be checked and topped up at the recommended temperate (I guess 'cold'?) and the reservoir is also known as an 'expansion tank' for that reason.
The car wasn't driven with the mixed coolant with more than about 5-8 (maximum 15 miles).

Would you than think that flushing the cooling system and changing the hoses on it could resolve the issues?

After your response I've done some research and most say it can cause serious damage to the head and also the injectors.

Now yesterday evening I had a friend over and because he hasn't yet seen the car I took him to it. We both sat in it. I turned the ignition on and a few seconds later the check coolant message came up. For some odd reason (completely sober) I thought would show him how it wouldn't start up), so I turned the key all the way. To my biggest surprise the engine fired up basically immediately. After a bit of shaking it started to run "normal". At the beginning it sounded like one of the cylinders wasn't working or something (I can't really tell due to my lack of knowledge). I switched it off. Looked under the car and there were a few drops of fuel under it. I popped the bonnet and opened the expansion tank to see if there was already pressure in it (it was only running for about a minute). There wasn't a massive one but could tell that the level of the coolant rose already. I decided to fire it up again, just to see what happens - not expecting any change, just because of curiosity. After the engine was running for about 2-3 minutes, the reservoir filled up and on this valve thingy on the side it looked like there was bubbles in it and started pouring the diesel again.

Regarding my previous estimates of about a 1/4 of a tank of loss, I saw that according to the gauge I mustn't have lost more than about 4-5 liters of fuel in the process when it happened with the mechanic for about 10 minutes. I must have been looking at the gauge from the wrong angle on that occasion. My stupidity has been established earlier as well, so I won't go in there with more detail.

I read a lot about injector cups failing making the diesel ending up in the coolant. This was also combined with idiots like me, who mixed coolants.

Now regarding the type of car I couldn't find such a thing as an injector cup which I assume makes the case worse. Would that mean that it doesn't come separate so it's basically certain that I damaged the cylinder head instead of something cheaper and easier to fix?
 

birolacoo

Standard Member
Bl4ckGryph0n is correct. The recommended coolant is G12. Normally a pinkish red cooler. As for the coolant smelling like diesel, diesel doesn't really have a smell. Petrol does, and a petrol leak you can smell a mile off (having replaced the fuel filter on a petrol Mk5 golf, which the fuel line was not correctly fitted the smell of petrol was overwhelming immediately, and I have a poor sense of smell).
Thanks. Once (or if) I manage to get it fixed I will definitely pay much more attention to details like this. I feel more and more stupid with a reason...
 

birolacoo

Standard Member
Now thinking about it, I feel like there might be two different issues as sort of established (?)

Please let me know if it's at all possible:

What we do know is that I mixed the coolants which fact on it's own can clog the cooling system and/or cause serious damage to the engine. This, to my understanding may result in the coolant smell odd (in this case sort of like diesel), and could also explain it to leak due to it's own pressure build up.

Should this be the case, could it mean that there's a separate reason for the massive fuel loss?

If so, what would your recommendations be? I mean, what could I check without experience and with the knowledge that is - how to put it - slightly limited to what I read on forums and watched on youtube during the past week or two?

Also, how can it be explained that the engine was not at all overheating if the cooling system wasn't working properly or at all?
 
It is cold outside ;) And the engine doesn't just overheat quickly by idling with these ambient temperatures.

I think there are two different issues, possibly three. I mean are you sure you are losing that much diesel or is the gauge broken ;) The coolant system definitely needs a full flush, but it does sound that there is a leak in it if it is bubbling. That is not good at all, but sometimes could be as simple as the lid not put on correctly, or leaking. Rather hard to remotely diagnose.
 

birolacoo

Standard Member
It is cold outside ;) And the engine doesn't just overheat quickly by idling with these ambient temperatures.

I think there are two different issues, possibly three. I mean are you sure you are losing that much diesel or is the gauge broken ;) The coolant system definitely needs a full flush, but it does sound that there is a leak in it if it is bubbling. That is not good at all, but sometimes could be as simple as the lid not put on correctly, or leaking. Rather hard to remotely diagnose.
I won't be able to respond in detail, but it wasn't idling.

At the time we drove to pick my daughter up from school. It's not a long trip, but includes different speed limits, so for the cca 3 miles we drove the car up to around 40 mph. As I mentioned above it didn't seem unusually quick to warm up to running temperature, but it may have been a little shorter. Not sure. As we stopped and realised there's this massive leak, my friend took a longer (time wise) route home (to avoid the a breakdown on the A406 during the school run). The whole trip there and back shouldn't have taken more than about 40-50 minutes (13ish there and the rest on the way back), but I'd think it would have definitely overheated during that time. Again, I won't be surprised if I'm wrong. And yes, as I recall it was a pretty cold day.

Lucky enough, I didn't refill anything else... (Other than the washer fluid and diesel).

I can't be sure at this point about the gauge. You're right. What I can't really explain - if the gauge is broken and I'm not losing fuel - is, what is the massive amount of diesel-smelling liquid ending up under the car when there doesn't seem to be a loss (moreover there's an increase) in the coolanin system and the oil level stays the same. Where is it coming from, if it's not fuel?
 
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LOL I'm so confused about the timeline now 🤣

a. It is normal for the expansion tank to seem to increase in volume, that is why it is an expansion tank 👍 What is not normal is that it starts bubbling. Now there could be several reasons for that varying from not a big deal, to a really big deal. For example, there could be air in the system that is trying to get out; definitely a possibility if you have been mixing incompatible coolant fluids. And in the worst-case scenario it indicates exhaust gases entering the coolant system, considering you suggest it smells that is a possibility and that may indicate either the beginning of a head gasket or total failure (unlikely if you aren't losing coolant).

b. Fuel on the ground underneath the car. That does suggest a fuel leak, that would need to be investigated.

I know it is not what you want to hear, but I wouldn't want to be driving around with a car that leaks fuel. Not just for my own safety; whilst it is combustible it isn't as flammable as petrol. However, it is slippery and I wouldn't want it on my knowledge if say a motorbike slipped on it and crashed.

I would get a mechanic back asap to take a look and diagnose the various issues and give you a quote. They may charge a call-out fee I'm afraid.
 

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