Coolant boiling in the block on stopping
Discussion
I've got a bit of a problem on my 3.9 V8 Wedge (390SE) - When I stop the engine on a hot day, the coolant tends to boil in the block, escape through the pressure cap into the auxiliary tank and then down the inside of the wing.
If I start up again shortly after stopping, and let the engine pump the coolant around, then it's generally OK. The odd thing is that when I arrive home, the water temp gauge is generally reading about 90 degrees.
Could it be:
a) Header tank pressure cap seal (it seems ok, both the cap and seat look clean and it appears to make contact and spring away by about 5mm when the cap is mostly tight, but I don't know what pressure it's acheiving)
b) Something wrong in the block (blocked passageway giving a hotspot which stores heat - surely it ought not to get appreciably hotter after stopping unless there's a store of heat round the cylinder which is still flowing towards the water passages - could this be a blocked water passage?)
c) 90 degrees on the gauge translates to 130 in the pipework? Do the gauges tend to be wrong? Sampling the wrong area?
d) My coolant (about the right mix at around 40% as far as I know) has mysteriously started boiling at 80... Doesn't seem possible that it's boiling point is 100 or less.
The odd thing is that no matter how much work the engine's doing on a hot day it never seems to boil up when running - but almost instantly on stopping.
Anyone have any good ideas? Things to try?
My next thing to do is probably going to be to pull a hose off, put a pressure gauge on the water system and see if I can test the header tank pressure valve release pressure (apparently 15psi according to the cap)
Thanks!
edit: Might be a good idea to give car model - oops!
If I start up again shortly after stopping, and let the engine pump the coolant around, then it's generally OK. The odd thing is that when I arrive home, the water temp gauge is generally reading about 90 degrees.
Could it be:
a) Header tank pressure cap seal (it seems ok, both the cap and seat look clean and it appears to make contact and spring away by about 5mm when the cap is mostly tight, but I don't know what pressure it's acheiving)
b) Something wrong in the block (blocked passageway giving a hotspot which stores heat - surely it ought not to get appreciably hotter after stopping unless there's a store of heat round the cylinder which is still flowing towards the water passages - could this be a blocked water passage?)
c) 90 degrees on the gauge translates to 130 in the pipework? Do the gauges tend to be wrong? Sampling the wrong area?
d) My coolant (about the right mix at around 40% as far as I know) has mysteriously started boiling at 80... Doesn't seem possible that it's boiling point is 100 or less.
The odd thing is that no matter how much work the engine's doing on a hot day it never seems to boil up when running - but almost instantly on stopping.
Anyone have any good ideas? Things to try?
My next thing to do is probably going to be to pull a hose off, put a pressure gauge on the water system and see if I can test the header tank pressure valve release pressure (apparently 15psi according to the cap)
Thanks!
edit: Might be a good idea to give car model - oops!
Edited by trs998 on Saturday 12th September 16:21
The engine heats up when you switch off as the circulation stops and the heat soaks in from the heads. If it's close to boiling, this might be enough to push it over. In that case either the engine is hotter than it should be, or the system isn't holding pressure. Since you say the gauge reading looks OK, I'd suspect it's lack of pressure.
The next question being... can anyone tell me where to find the offending cap? Is it standard rover v8? Or is it some sort of TVR different pressure?
"rover v8 coolant header tank cap" doesn't give me any sensible results on google (all mg rover owners with exploding head gaskets)
Can't find much in the way of wedge suppliers... Tamsin was dropped when the v8 came in, so that's probably not a good cue.
Anyone recommend a good norfolk supplier or one that does mail order?
"rover v8 coolant header tank cap" doesn't give me any sensible results on google (all mg rover owners with exploding head gaskets)
Can't find much in the way of wedge suppliers... Tamsin was dropped when the v8 came in, so that's probably not a good cue.
Anyone recommend a good norfolk supplier or one that does mail order?
trs - your original post and the reply imply that you have a sprung pressure cap on the swan-neck.
I hope that you haven't, the swan-neck should simply have a blank (flat) cap with no spring, just a flat rubber seal.
The reservoir in the wing should have the sprung pressure cap, its overflow is often just a simple rubber pipe which on mine (1985 390) ran down the inner wing and vented to the atmosphere. Is your "auxillary" the reservoir bottle or do you have a catch bottle on the output of the reservoir vent pipe?
The spring on the cap should be 14-15psi, a fairly common value (others are 8psi).
There are two reasons for boiling: -
1) Overheating - the engine is overheating somehow or could be suffering from individual hot-spots or lack of water circulation. This can be caused by over-advanced timing or by a blocked radiator. Use of hard water can cause sediments/crusting that can also cause localised boiling. I have never tried it but does Calgon work against this, boiling the water before filling the system or using pure rain-water guards against calcification.
2) Low pressure - the spring on the pressure cap vents too early and the water boils at just over 100C instead of a higher temperature, it should reach about 110C-115C before boiling. The boiling point can be raised a little by adding antifreeze.
Another cause could be air trapped in the system that can appear to be boiling - but this often manifests itself in different ways than your symptoms.
Russ
I hope that you haven't, the swan-neck should simply have a blank (flat) cap with no spring, just a flat rubber seal.
The reservoir in the wing should have the sprung pressure cap, its overflow is often just a simple rubber pipe which on mine (1985 390) ran down the inner wing and vented to the atmosphere. Is your "auxillary" the reservoir bottle or do you have a catch bottle on the output of the reservoir vent pipe?
The spring on the cap should be 14-15psi, a fairly common value (others are 8psi).
There are two reasons for boiling: -
1) Overheating - the engine is overheating somehow or could be suffering from individual hot-spots or lack of water circulation. This can be caused by over-advanced timing or by a blocked radiator. Use of hard water can cause sediments/crusting that can also cause localised boiling. I have never tried it but does Calgon work against this, boiling the water before filling the system or using pure rain-water guards against calcification.
2) Low pressure - the spring on the pressure cap vents too early and the water boils at just over 100C instead of a higher temperature, it should reach about 110C-115C before boiling. The boiling point can be raised a little by adding antifreeze.
Another cause could be air trapped in the system that can appear to be boiling - but this often manifests itself in different ways than your symptoms.
Russ
trs998 said:
I've got a bit of a problem on my 3.9 V8 Wedge (390SE) - When I stop the engine on a hot day, the coolant tends to boil in the block, escape through the pressure cap into the auxiliary tank and then down the inside of the wing.
If I start up again shortly after stopping, and let the engine pump the coolant around, then it's generally OK. The odd thing is that when I arrive home, the water temp gauge is generally reading about 90 degrees.
Could it be:
a) Header tank pressure cap seal (it seems ok, both the cap and seat look clean and it appears to make contact and spring away by about 5mm when the cap is mostly tight, but I don't know what pressure it's acheiving)
b) Something wrong in the block (blocked passageway giving a hotspot which stores heat - surely it ought not to get appreciably hotter after stopping unless there's a store of heat round the cylinder which is still flowing towards the water passages - could this be a blocked water passage?)
c) 90 degrees on the gauge translates to 130 in the pipework? Do the gauges tend to be wrong? Sampling the wrong area?
d) My coolant (about the right mix at around 40% as far as I know) has mysteriously started boiling at 80... Doesn't seem possible that it's boiling point is 100 or less.
The odd thing is that no matter how much work the engine's doing on a hot day it never seems to boil up when running - but almost instantly on stopping.
Anyone have any good ideas? Things to try?
My next thing to do is probably going to be to pull a hose off, put a pressure gauge on the water system and see if I can test the header tank pressure valve release pressure (apparently 15psi according to the cap)
Thanks!
edit: Might be a good idea to give car model - oops!
Hi Tristan, i,ve got a problem the same as yours,[350 model] when travelling car sits at around 84 degrees, no problem, but when i slow down going through a town it goes up to 90 degrees, i think i,ve got some sediment in the rad as one of the lads said above, i,ve changed the cap as well [15lbs]If I start up again shortly after stopping, and let the engine pump the coolant around, then it's generally OK. The odd thing is that when I arrive home, the water temp gauge is generally reading about 90 degrees.
Could it be:
a) Header tank pressure cap seal (it seems ok, both the cap and seat look clean and it appears to make contact and spring away by about 5mm when the cap is mostly tight, but I don't know what pressure it's acheiving)
b) Something wrong in the block (blocked passageway giving a hotspot which stores heat - surely it ought not to get appreciably hotter after stopping unless there's a store of heat round the cylinder which is still flowing towards the water passages - could this be a blocked water passage?)
c) 90 degrees on the gauge translates to 130 in the pipework? Do the gauges tend to be wrong? Sampling the wrong area?
d) My coolant (about the right mix at around 40% as far as I know) has mysteriously started boiling at 80... Doesn't seem possible that it's boiling point is 100 or less.
The odd thing is that no matter how much work the engine's doing on a hot day it never seems to boil up when running - but almost instantly on stopping.
Anyone have any good ideas? Things to try?
My next thing to do is probably going to be to pull a hose off, put a pressure gauge on the water system and see if I can test the header tank pressure valve release pressure (apparently 15psi according to the cap)
Thanks!
edit: Might be a good idea to give car model - oops!
Edited by trs998 on Saturday 12th September 16:21
I think i'm going to have to drain and flush the system and check hoses for small leaks. I did turn the kenlowe gauge down to 84 so that it comes on earlier to keep cooler but still heats up.So if i come up with a solution i'll keep you posted if not and you have solved it please keep me posted.
regards jonny...
trs998 said:
I've got a bit of a problem on my 3.9 V8 Wedge (390SE) - When I stop the engine on a hot day, the coolant tends to boil in the block, escape through the pressure cap into the auxiliary tank and then down the inside of the wing.
If I start up again shortly after stopping, and let the engine pump the coolant around, then it's generally OK. The odd thing is that when I arrive home, the water temp gauge is generally reading about 90 degrees.
Could it be:
a) Header tank pressure cap seal (it seems ok, both the cap and seat look clean and it appears to make contact and spring away by about 5mm when the cap is mostly tight, but I don't know what pressure it's acheiving)
b) Something wrong in the block (blocked passageway giving a hotspot which stores heat - surely it ought not to get appreciably hotter after stopping unless there's a store of heat round the cylinder which is still flowing towards the water passages - could this be a blocked water passage?)
c) 90 degrees on the gauge translates to 130 in the pipework? Do the gauges tend to be wrong? Sampling the wrong area?
d) My coolant (about the right mix at around 40% as far as I know) has mysteriously started boiling at 80... Doesn't seem possible that it's boiling point is 100 or less.
The odd thing is that no matter how much work the engine's doing on a hot day it never seems to boil up when running - but almost instantly on stopping.
Anyone have any good ideas? Things to try?
My next thing to do is probably going to be to pull a hose off, put a pressure gauge on the water system and see if I can test the header tank pressure valve release pressure (apparently 15psi according to the cap)
Thanks!
edit: Might be a good idea to give car model - oops!
Hi Tristan, i,ve got a problem the same as yours,[350 model] when travelling car sits at around 84 degrees, no problem, but when i slow down going through a town it goes up to 90 degrees, i think i,ve got some sediment in the rad as one of the lads said above, i,ve changed the cap as well [15lbs]If I start up again shortly after stopping, and let the engine pump the coolant around, then it's generally OK. The odd thing is that when I arrive home, the water temp gauge is generally reading about 90 degrees.
Could it be:
a) Header tank pressure cap seal (it seems ok, both the cap and seat look clean and it appears to make contact and spring away by about 5mm when the cap is mostly tight, but I don't know what pressure it's acheiving)
b) Something wrong in the block (blocked passageway giving a hotspot which stores heat - surely it ought not to get appreciably hotter after stopping unless there's a store of heat round the cylinder which is still flowing towards the water passages - could this be a blocked water passage?)
c) 90 degrees on the gauge translates to 130 in the pipework? Do the gauges tend to be wrong? Sampling the wrong area?
d) My coolant (about the right mix at around 40% as far as I know) has mysteriously started boiling at 80... Doesn't seem possible that it's boiling point is 100 or less.
The odd thing is that no matter how much work the engine's doing on a hot day it never seems to boil up when running - but almost instantly on stopping.
Anyone have any good ideas? Things to try?
My next thing to do is probably going to be to pull a hose off, put a pressure gauge on the water system and see if I can test the header tank pressure valve release pressure (apparently 15psi according to the cap)
Thanks!
edit: Might be a good idea to give car model - oops!
Edited by trs998 on Saturday 12th September 16:21
I think i'm going to have to drain and flush the system and check hoses for small leaks. I did turn the kenlowe gauge down to 84 so that it comes on earlier to keep cooler but still heats up.So if i come up with a solution i'll keep you posted if not and you have solved it please keep me posted.
regards jonny...
Hmm, this one's come up again. It turns out with some measuring, that the cap I have (supplied by Adam Quantrill) fits the top of the bottle, but the spring inner pressure seal sits clear of the inner mating face by 1mm, ergo zero coolant pressure. With the fans on, the car loses coolant slowly (I guess after a good flush out before running this year the cooling system is largely working ok) - I can run around usually, but find myself having to top up coolant. It's been a problem in the recent hot weather.
However, this means the cap won't work. I am looking at either:
1) replacing the header tank (ford capri mk3 2.8) and getting a cap for that (can't source one)
2) replacing the cap (with what? I assume the normal part from Adam normally works, so is my tank wrong?)
3) Modifying the cap to reach further (maybe add a 3/4mm washer to it?)
However, this means the cap won't work. I am looking at either:
1) replacing the header tank (ford capri mk3 2.8) and getting a cap for that (can't source one)
2) replacing the cap (with what? I assume the normal part from Adam normally works, so is my tank wrong?)
3) Modifying the cap to reach further (maybe add a 3/4mm washer to it?)
Actually these caps work better with a catch tank.
The inner small sprung brass bit allows the coolant system to suck coolant back in from the catch tank.
Reading your original post your header tank overflow does to a hose down to the ground. Take this off, and put on a PVC plastic pipe to a one litre bottle or tank at the same level as the expansion tank. Make sure the hose goes to the bottom of this second tank.
Occasionally bits of crud get caught under the little brass washer and it start leaking, so you may need to check/clean it occasionally.
The inner small sprung brass bit allows the coolant system to suck coolant back in from the catch tank.
Reading your original post your header tank overflow does to a hose down to the ground. Take this off, and put on a PVC plastic pipe to a one litre bottle or tank at the same level as the expansion tank. Make sure the hose goes to the bottom of this second tank.
Occasionally bits of crud get caught under the little brass washer and it start leaking, so you may need to check/clean it occasionally.
trs998 said:
Hmm, this one's come up again. It turns out with some measuring, that the cap I have (supplied by Adam Quantrill) fits the top of the bottle, but the spring inner pressure seal sits clear of the inner mating face by 1mm, ergo zero coolant pressure. With the fans on, the car loses coolant slowly (I guess after a good flush out before running this year the cooling system is largely working ok) - I can run around usually, but find myself having to top up coolant. It's been a problem in the recent hot weather.
However, this means the cap won't work. I am looking at either:
1) replacing the header tank (ford capri mk3 2.8) and getting a cap for that (can't source one)
2) replacing the cap (with what? I assume the normal part from Adam normally works, so is my tank wrong?)
3) Modifying the cap to reach further (maybe add a 3/4mm washer to it?)
Hi Mate...A standard size pressure rad cap should fit on the header tank, I think an E-type cap..(Non- pressure) fits on the swan neck?..If your coolant is boiling then you must have a leak somewhere, Do you have an electric cooling fan/Fans and if so you might be able to run them for a short time after via a thermostatic contol, Is your temperature sender of the correct operating temp?...Ziga However, this means the cap won't work. I am looking at either:
1) replacing the header tank (ford capri mk3 2.8) and getting a cap for that (can't source one)
2) replacing the cap (with what? I assume the normal part from Adam normally works, so is my tank wrong?)
3) Modifying the cap to reach further (maybe add a 3/4mm washer to it?)
mrzigazaga said:
Hi Mate...A standard size pressure rad cap should fit on the header tank, I think an E-type cap..(Non- pressure) fits on the swan neck?..If your coolant is boiling then you must have a leak somewhere, Do you have an electric cooling fan/Fans and if so you might be able to run them for a short time after via a thermostatic contol, Is your temperature sender of the correct operating temp?...Ziga
hi all of the things listed in the posts maybe the problem........but it sounds like your orginal pressure cap is doing what i should (as identifed by Mark), allowing the expanding mass to escape when air is addedthe first easy policy is to replace one thing at a time, a cheap one to replace is the cap on the swan neck, make sure is tight down and sitting on the rubber,bend those tabs and knock on with a hammer (put the original pressure cap back on).
(had the same problem with both of mine)
if the water is still coming out of the expansion bottle, change the pressure cap.
keep your fingers crossed that solves because the rest is a bit more work !
best of luck
Had similar symptoms on a V6 MR2 which turned out to be the water pump being patent part. the vanes weren't up to giving enough flow at idle and so the car would slowly overheat but after a short duration of 2000 odd rpm revs it would cool down again. Is it possibly something to do with the water pump?
When it's boiling, there's no leak around the swan neck - I'm satisfied this is a good seal.
When started cold, with the header tank brimming full, where is no bubbles or movement to suggest combustion gases in the coolant, even with some throttle and revs. When the engine is revved up a bit the level dips a little and returns as the revs drop, which is what I'd expect - the pump's running faster and so therefore the rubber hoses stretch a little. Therefore I think the water pump is working fine. Can't vouch for correct flow rate, but it's a plausible flow rate.
I have a single electric fan, which is on manual control (switch on the column) - in this weather I normally switch it on pretty much straight away, leave it on permanently while driving, then turn it off again about 5 minutes after I stop the engine. Some sort of timer which could also run an auxiliary water circulation pump with the engine stopped for a few minutes would be a good modification to do. The fan seems to work perfectly, apart from the lack of automatic control.
Temperature sender (reading on the dial) matches all the temperatures read with my temperature gun - all the hoses are in the region of the dial, which normally reads around 80 at speed, creeping to 90/95 in slow traffic.
I measured the cap from top washer to the end of the spring washer, and got 18mm, with the spring in it's normal "rest" position.
I measured the offset between the top of the tank (where the top washer lands) and the bottom (where the sprung washer lands) and it's 19mm.
Ergo, the sprung washer is not making contact. If this is the normal cap (i think it is) then maybe my tank isn't the normal tank?
oh, and I have the overflow/recovery tank which works well, though generally there is always coolant lost as steam and overflowing the tank, so every run it needs multiple litres of replacement.
When started cold, with the header tank brimming full, where is no bubbles or movement to suggest combustion gases in the coolant, even with some throttle and revs. When the engine is revved up a bit the level dips a little and returns as the revs drop, which is what I'd expect - the pump's running faster and so therefore the rubber hoses stretch a little. Therefore I think the water pump is working fine. Can't vouch for correct flow rate, but it's a plausible flow rate.
I have a single electric fan, which is on manual control (switch on the column) - in this weather I normally switch it on pretty much straight away, leave it on permanently while driving, then turn it off again about 5 minutes after I stop the engine. Some sort of timer which could also run an auxiliary water circulation pump with the engine stopped for a few minutes would be a good modification to do. The fan seems to work perfectly, apart from the lack of automatic control.
Temperature sender (reading on the dial) matches all the temperatures read with my temperature gun - all the hoses are in the region of the dial, which normally reads around 80 at speed, creeping to 90/95 in slow traffic.
I measured the cap from top washer to the end of the spring washer, and got 18mm, with the spring in it's normal "rest" position.
I measured the offset between the top of the tank (where the top washer lands) and the bottom (where the sprung washer lands) and it's 19mm.
Ergo, the sprung washer is not making contact. If this is the normal cap (i think it is) then maybe my tank isn't the normal tank?
oh, and I have the overflow/recovery tank which works well, though generally there is always coolant lost as steam and overflowing the tank, so every run it needs multiple litres of replacement.
Looking on errbay, there's a short version (1" reach) and a long version (34mm reach) - I'll order the long reach version and see if that makes any difference, for £7 I think it's worth a shot.
http://www.ebay.co.uk/itm/RADIATOR-CAP-4LB-LONG-RE...
http://www.ebay.co.uk/itm/RADIATOR-CAP-4LB-LONG-RE...
Hi Mate..Just a thought..On the V6 which shares the same expansion tank..(Ford capri/granada 2.8i) as the V8's the top up level is just under the tip of the plastic indicator inside the tank which is visible from the opening...However i have noticed that the two inlets/outlets on the same side are capped off on the V8 fitment whereas on the V6 are actually used to aid the flow..I have also seen V8's that have the water topped up too high which results in overflowing coolant..Could this be the matter in your case..Can anyone confirm this as i seem to recall a much lower level in the V8 expansion tank set up..Probably nearer to an inch covering the bottom?...Cheers..Ziga
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