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 still wouldn't rule out an air lock in the system. In typical TVR fashion they decided to re-plumb how the 350 was set up by Rover without any improvement in performance.
Reverting to the 'SD1' cooling set up works and is a self bleeding system (rendering the open overflow resevoir redundant). Now there is a thread in this forum on how to do it, just where ..
ETA - Alternative radiator install here - https://www.pistonheads.com/gassing/topic.asp?h=0&... - handy if you're going to overhall the system.
Replumbing of the hoses - https://www.pistonheads.com/gassing/topic.asp?h=0&... - system now self bleeds and can be filled from the expansion tank. You can, if you so desire, then replace the swan neck (with a 90-degree pipe), thermostat housing [as used on the chimp and grief] and striht pipe which moves the connection pipework off to the side and removes the filling point.
Reverting to the 'SD1' cooling set up works and is a self bleeding system (rendering the open overflow resevoir redundant). Now there is a thread in this forum on how to do it, just where ..
ETA - Alternative radiator install here - https://www.pistonheads.com/gassing/topic.asp?h=0&... - handy if you're going to overhall the system.
Replumbing of the hoses - https://www.pistonheads.com/gassing/topic.asp?h=0&... - system now self bleeds and can be filled from the expansion tank. You can, if you so desire, then replace the swan neck (with a 90-degree pipe), thermostat housing [as used on the chimp and grief] and striht pipe which moves the connection pipework off to the side and removes the filling point.
Edited by mk1fan on Tuesday 27th June 10:57
keynsham said:
There is a self-test kit you can get to check for hydrocarbons in the coolant but currently I have the exhaust off and you have to run the engine for the kit to work! It could be a little noisy!!
Wouldn't the hydrocarbons already be in the coolant though - If the engine's been running with a gasket leak, or do the HC's in suspension reduce with time?
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.
A surefire way of knowing without removing heads and the like is the sniff test. You already know about the engine has to be running for the gasses to run through the liquid for it to detect noxious gases are present.
It's a 50/50 chance that you choose the correct head to remove. However, my guess is the starting point would be the lower compression side first.
Are you sure that the water pump and stat are in good order?
It's a 50/50 chance that you choose the correct head to remove. However, my guess is the starting point would be the lower compression side first.
Are you sure that the water pump and stat are in good order?
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!
Presumably because the wedge constantly pumps water through the expansion tank, a restriction or blockage on the return path could also cause water to spew out.
I'm guessing from the original post that the system has chucked water out allowing air in causing the erratic temp gauge.
Weirdly I had a similar issue with mine and I ended up replacing the expansion tank which cured the problem. I could only put the issue down to the fact that the radiator cap barely tightened up on the old expansion tank which was worn down from 30+ years of people checking the water level I guess....
I did always wonder whether you could use those sniff test devices on a wedge, or if they'd just fill up with water - perhaps you need to convert the cooling back to SD1 first as someone mentioned above.
I'm guessing from the original post that the system has chucked water out allowing air in causing the erratic temp gauge.
Weirdly I had a similar issue with mine and I ended up replacing the expansion tank which cured the problem. I could only put the issue down to the fact that the radiator cap barely tightened up on the old expansion tank which was worn down from 30+ years of people checking the water level I guess....
I did always wonder whether you could use those sniff test devices on a wedge, or if they'd just fill up with water - perhaps you need to convert the cooling back to SD1 first as someone mentioned above.
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.
I don't know if the exhaust is still disconnected 
....... Is it possible to disconnect the expansion tank and just use the radiator with a pressure cap - like a 'vintage' set-up based on an early system used for that engine? Unlikely, I'm sure, but it may then identify if exhaust gases are getting in the waterways. Just thinking aloud, if the exhaust is back on, I guess you could use the 'sniffer' manometer gadget.
....... Is it possible to disconnect the expansion tank and just use the radiator with a pressure cap - like a 'vintage' set-up based on an early system used for that engine? Unlikely, I'm sure, but it may then identify if exhaust gases are getting in the waterways. Just thinking aloud, if the exhaust is back on, I guess you could use the 'sniffer' manometer gadget.I'm on to my third V8 Wedge and the cooling system were all the same. I brim the Swan neck via the blanking cap (it's not a pressure cap), and fill the expansion tank to the internal plastic level marker, which is about 2" down from top. I also ensure the small bore over flow pipe reaches the bottom of the overflow tank (its a TR7 washer bottle by the way) and I ensure the overflow tank is about a third full. I also jubilee clip the overflow hose. Then when the expansion tank expends air or fluid, it fills the overflow bottle. As it cools it will draw the coolant back in from overflow to expansion tank. Its important the overflow pipe is air tight so it sucks the overflow coolant back and not air from a bad hose joint.
Head gasket all day long. Get an Elring set - they are the bees knees. Might be harder to find for the 350i. Also replace the valley gasket while you're there.
As for testing the coolant, most people forget that the predominant gases being pumped into it are Nitrogen (which we can ignore) and Carbon Dioxide.
So I do the "lime water" test, yes the same one from school chemistry, bubble the gases through lime water (which you can make yourself). If it goes cloudy, you've made calcium carbonate, which shows up the CO2.
As for testing the coolant, most people forget that the predominant gases being pumped into it are Nitrogen (which we can ignore) and Carbon Dioxide.
So I do the "lime water" test, yes the same one from school chemistry, bubble the gases through lime water (which you can make yourself). If it goes cloudy, you've made calcium carbonate, which shows up the CO2.
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!!
Knackered pressure cap? I always run a 16psi unit. One of these...
https://www.burtonpower.com/motorad-radiator-cap-1...
https://www.burtonpower.com/motorad-radiator-cap-1...
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!!
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