Possible Head Gasket Failure
Discussion
I have been having some problems with the cooling system on my 350i. The gauge usually sits in the middle but occasionally goes up to the red and then after a few minutes, drops back quickly. I had assumed there was air trapped in the system but I think it might be a little more sinister than that as I have bled it a number of times, but it always seems to come back.
The other issue I have is that I noticed that not only does my expansion tank fill completely, but the overflow tank also does and can even leak out of the top. if I start the engine from cold with the expansion tank top off, the tank slowly fills and within a few minutes, if I don't replace the cap, it overflows.
From what I have read, it is looking likely that I have a head gasket issue which is leaking into the coolant and pressurizing the cooling system and pushing the coolant out of the expansion tank.
Does anyone have any experience of this? I will do a compression test tomorrow to see if that highlights any issues.
The other issue I have is that I noticed that not only does my expansion tank fill completely, but the overflow tank also does and can even leak out of the top. if I start the engine from cold with the expansion tank top off, the tank slowly fills and within a few minutes, if I don't replace the cap, it overflows.
From what I have read, it is looking likely that I have a head gasket issue which is leaking into the coolant and pressurizing the cooling system and pushing the coolant out of the expansion tank.
Does anyone have any experience of this? I will do a compression test tomorrow to see if that highlights any issues.
I have just done a compression test on all cylinders and the readings were as follows:
Near Side, Rear to front: 190 200 190 190
Offside Rear, to front: 190 200 200 175
This was done cold but as I have no exhaust at the moment, I thought it best for the neighbours! Quite healthy figures too for a 350i with 82k miles on I thought!
My thoughts are still that the head gasket is leaking into the cooling system and pressurising it to push the coolant out of the expansion tank. Having racked my brains, I cannot think of any other process which would cause this.
The 175 value could of course be a badly seating valve but until I can get inside and have a poke around, I am not going to know.
Near Side, Rear to front: 190 200 190 190
Offside Rear, to front: 190 200 200 175
This was done cold but as I have no exhaust at the moment, I thought it best for the neighbours! Quite healthy figures too for a 350i with 82k miles on I thought!
My thoughts are still that the head gasket is leaking into the cooling system and pressurising it to push the coolant out of the expansion tank. Having racked my brains, I cannot think of any other process which would cause this.
The 175 value could of course be a badly seating valve but until I can get inside and have a poke around, I am not going to know.
Yes, water pump and thermostat are working fine. to be honest I am happy to take the top off. I want to check the camshaft. I don't plan to replace it if it is fine, so I am going to measure the lift of each cam with a dial gauge. Also, I can check valves, seals etc whilst I am in there! It really isn't a difficult task on a V8 Rover engine. I have had this one apart before to fix oil leaks (not heads off though!) and I have rebuilt my Rover P6 3500 a few times over the years.
I cannot think of anything other than a leaky head gasket that could pressurize the coolant system and push the water out of the expansion tank so i'm going in!!!
I'll post a few pictures when I have something to report!
I cannot think of anything other than a leaky head gasket that could pressurize the coolant system and push the water out of the expansion tank so i'm going in!!!
I'll post a few pictures when I have something to report!
So I have had a major rethink about my problem, and after the helpful comments from Pumpkin123 (Thanks!), I think this may have been operator error on my behalf!
What I didn't realize was that the coolant actually continuously flows through the expansion tank. I only had the tank around 1/3 full so when the water flowed in, air was getting sucked out of the top pipe and straight into the system. I had assumed, wrongly, that the coolant was going to overflow because I don't think I left it long enough as ir rose to see it get sucked down the top pipe before I chickened out and refitted the pressure cap.
This would then mean I had a system already full of air which when the engine warmed up, caused havoc!
So my question now is, should the expansion tank be fully filled when cold to above the upper outlet pipe?
This also explains why there is an overflow tank next to the expansion tank because if the expansion tank runs full when cold, any expansion in the warm engine will force it to overflow.
What I didn't realize was that the coolant actually continuously flows through the expansion tank. I only had the tank around 1/3 full so when the water flowed in, air was getting sucked out of the top pipe and straight into the system. I had assumed, wrongly, that the coolant was going to overflow because I don't think I left it long enough as ir rose to see it get sucked down the top pipe before I chickened out and refitted the pressure cap.
This would then mean I had a system already full of air which when the engine warmed up, caused havoc!
So my question now is, should the expansion tank be fully filled when cold to above the upper outlet pipe?
This also explains why there is an overflow tank next to the expansion tank because if the expansion tank runs full when cold, any expansion in the warm engine will force it to overflow.
So for today's update.....
Having checked my cooling system thoroughly for leaks, and working out how much to fill the expansion tank, I did the following:
1. Fill the expansion tank to the mark on the level 'finger' that sticks up inside the expansion tank. This makes the coolant level about 20mm above the side exit pipe.
2. Put about 20mm of coolant in the overflow bottle so the overflow pipe sits in it and no air can get sucked back in.
3. Filled the swan neck as much as I could, run the engine, bleed out any air and replace cap.
I then ran the engine on idle until the temperature got high enough for the fan to cut in. I left it running for about 20 mins and all was fine.
So I decided to take it for a road test..........
All good for the first few miles and then the temp gauge started doing its up and down thing so I know something was wrong.
When I got home I opened the bonnet. The inner wing was wet as was the bonnet underside. The overflow bottle was completely full and overflowing. (it was actually bubbling which I think was caused from gas getting pushed out of the expansion tank) There was a puddle of coolant underneath it. I pulled the pipe out of the overflow tank and put my finger over the end. There was slight pressure building up in it but nothing much. I carefully took off the expansion tank top and not even a hiss. The expansion tank was completely empty!
So I am back to my head gasket theory. Somewhere there is gas pressure building up and pushing the coolant out of the system and I cannot think where else it could be from.
Any comments, ideas, or theories, however crazy, are more than welcome!!
Having checked my cooling system thoroughly for leaks, and working out how much to fill the expansion tank, I did the following:
1. Fill the expansion tank to the mark on the level 'finger' that sticks up inside the expansion tank. This makes the coolant level about 20mm above the side exit pipe.
2. Put about 20mm of coolant in the overflow bottle so the overflow pipe sits in it and no air can get sucked back in.
3. Filled the swan neck as much as I could, run the engine, bleed out any air and replace cap.
I then ran the engine on idle until the temperature got high enough for the fan to cut in. I left it running for about 20 mins and all was fine.
So I decided to take it for a road test..........
All good for the first few miles and then the temp gauge started doing its up and down thing so I know something was wrong.
When I got home I opened the bonnet. The inner wing was wet as was the bonnet underside. The overflow bottle was completely full and overflowing. (it was actually bubbling which I think was caused from gas getting pushed out of the expansion tank) There was a puddle of coolant underneath it. I pulled the pipe out of the overflow tank and put my finger over the end. There was slight pressure building up in it but nothing much. I carefully took off the expansion tank top and not even a hiss. The expansion tank was completely empty!
So I am back to my head gasket theory. Somewhere there is gas pressure building up and pushing the coolant out of the system and I cannot think where else it could be from.
Any comments, ideas, or theories, however crazy, are more than welcome!!
I have just done a test with a kit which detects exhaust gases in the air escaping from the expansion tank.
It should look and stay like this:
If there are exhaust gasses present, it goes a yellow/green colour, like this: (As mine has below!)
So there you go, head gasket failure! I now have the best excuse in the world to strip the top off my engine and replace the camshaft at the same time!!
It should look and stay like this:
If there are exhaust gasses present, it goes a yellow/green colour, like this: (As mine has below!)
So there you go, head gasket failure! I now have the best excuse in the world to strip the top off my engine and replace the camshaft at the same time!!
So head is off and I have found the problem. It seems the head gasket was corroding away and had started leaking between the water gallery and rear cylinder of the offside bank. I had a measure of my camshaft whilst I was in there and that has some wear too so it will be replaced at the same time.
The cam needs doing. Standard lift is 0.39" which equates to 0.26" at the lobe after allowing for the 1.5 factor from the rocker advantage. I measured a few of my cam lobes and they are around 0.245", making valve lift 0.3675" or thereabouts, which is a 6% reduction on production. Put into perspective, medium road cams seem to be around 0.42" lift which is around 7% greater than production standard and 13% greater than my worn cam, so a whopping 1.33mm greater valve lift! I'm in there now anyway, and I love taking engines apart so it is just a case of which cam!!!
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