Coolant level changing

[adamnreeves]

Ramon,

you trying to scare me! I should just add that when the water over flowed it was not boiling. I started the car, pulled it out the garage and it happened then. coolant temperature was less than 60c. It has only done this once and the previous evening I had topped the system up.

The cap has a built in valve and this just vents down four channels running 90degrees to the threads to the outside

I've just finishing t'ing in the highest part of the inlet manifold into the overflow to the expansion tank.

Ran the electric water pump with engine off and the coolant level no longer changes it level like it did before.

Just been for a run out now for about 30 minutes. Temperature seems more stable now but I am not going to say this has solved it yet because it has been stable before. Ran the car on idle when I got back until the fan kicked it, which wasn't long. 90c, turned off, no glugging noises but I can hear a whisper of air around the pressure cap. This cap was brand new. Do you think I ought to change it?

[ramon alban]

you trying to scare me! I should just add that when the water over flowed it was not boiling.

Not at all Adam, just trying to exercise the ol' grey matter, working on your reported symptoms of a system unfamiliar to me!

1 Your continual topping up makes it certain that there is air in the system. Air and fluid are both being expelled instead of only air from the header tank.

2 Your unexpected coolant leaking via the cap and hissing thereabouts, seriously suggests a low pressure situation.

3 Water boils at a much lower temperature when the pressure is low. No internal pressure = 100 deg C, 15 psi = 125 deg C, before adding antifreeze which raises the boiling point a futher 10 deg C to approx 135 deg C. The whole ethos of the conventional RV8 cooling system is dependent upon there being high internal pressure in the region of 15 psi. Yours should be no different.

4 Because there is clearly air in the system, maybe even trapped in the vicinity of the heads/exhaust valves, its very existence would mean the flow of fluid past that area would be not necessarily take the air with it.

5 Air in any heating system has a habit of staying put, thats why we have to bleed our domestic radiators, - even the ones downstairs. Air locks are the bain of the RV8 cooling system.

6 When the engine starts the heat generated by the combustion process is exactly the same as if it was left idling for a few minutes. ie, the local heat is intense and must be cooled efficiently. Spit on the exhaust header and see how soon the temperature fizzles it away.

7 The waterjacket material around the cylinder heads and valves is quite thin, simply to get all the galleries and channels into the metal thereabouts, so, with aluminium being the best ever conductor of heat, means the heat is transferred to the water galleries very fast indeed.

8 If those galleries are partially devoid of coolant, then the generation of STEAM is guaranteed, just like the fizzling spit, and not dependent upon the temperature of the rest of the fluid in the vicinity.

9 Steam once generated, expands at an alarming rate (remember the James Wayy and his steam engine?) and its generation is not dependent upon the rest of the fluid boiling. Just the the mere fact that there is air in the system and the metal walls are very hot, causes it to appear.

10 so even after your relatively innocent

I started the car, pulled it out the garage and it happened then. coolant temperature was less than 60c.

Something sure as hell had the strength to push the fluid out, and, as explained such a temporary explosion of steam is what causes any coolant ot burp out as you describe. I mean! What else could it be, farting fish?????

11 And of course it should never have come out anyway unless the internal system pressure was higher than the pressure cap specification. (normally 15 psi).

Like I said, Double Jeopardy. Dont be scared - just be aware!

Check your system pressure, fix it if necessary, make sure ALL air is eliminated, and try again.

Re-reading your original and later posts I do have some further concerns.

# You were already worried about prior overheating before I suggested a cause.

# Your description of the plumbing

the outlet from the inlet manifold is piped into the header tank. So when the thermostat is closed then coolant is pumped into the header tank. Probably not ideal and I am hoping this is the problem.

seems to omit the return from inlet manifold to the water pump - going to the header tank instead - bringing into question how well the coolant may be circulating BEFORE thermostat opens. further exacerbating the possibility of initial overheating.

# it is absolutely vital that the coolant circulates fully using its "thermostat bypass circuit" whilst the system is waiting for the thermostat to open.

# You mention that a bleed valve is not accessible due to it being masked by the thermostat - so how does one eliminate air locks?

# One assumes that all these problems have come about since fitting a leccy water pump , presumably replacing the conventional water pump, in which case it would be prudent to find a way of testing the flow through the system prior to the thermostat being open.

Good Luck.

[adamnreeves]

The electric water pump is being used as a boost its located in the bottom hose between the radiator and the mechanical pump. I've been having inconsistent cooling problems from day 1. Its never over heated but been running higher than I'd like and inconsistent which I put down to an airlock. The engine is installed in a westfield where the top hose to the radiator is lower than the thermostat cover. I replaced the Rover thermostat cover which points upward with a striaght out one from JED. This has been installed for about 300miles and has made a difference, initially running without a thermostat. When I installed the electric I installed a Triumph thermostat which opens at 78c. This has a bleed hole at 12 o'clock position but I noticed that the JED thermostat cover blocks this so yes I was concerned about bleeding. The outlet that goes to the heater normally which is plumbed into the header tank allows circulation of coolant when stat is closed but obviously this is not good for removing trapped air. The smaller outlet at the top of the manifold that I have just plumbed in this afternoon will however. My coolant cap is still hising 1.5hrs after turning the engine off so its obviously not leaking much. Coolant temp is 50c. When I say hissing its just air no coolant leaking.
I am not constantly topping up the coolant either, only topped up once in over 2,000miles other than when I've replaced the coolant after installing the pump, thermostat cover of course. Like I say the only time I topped and it blew out the next time I started up. Thanks for your feedback and guidance, much appreciated.

Oh forgot about the farting fish. Before I t'eed the top of the manifold to the header tank if I siwtched on the electric water pump on a cold engine the level in the header tank goes up and stays there for hours. This still mystifies me.

[ramon alban]

The outlet that goes to the heater normally which is plumbed into the header tank allows circulation of coolant when stat is closed but obviously this is not good for removing trapped air. The smaller outlet at the top of the manifold that I have just plumbed in this afternoon will however. My coolant cap is still hising 1.5hrs after turning the engine off so its obviously not leaking much. Coolant temp is 50c. When I say hissing its just air no coolant leaking.

That latest plumbing change seems to have done the trick, then Adam? I hope however that you'll see why and where the diagnosis was going before taking that into account.

Regarding the hissing 1.5 hours after switching off, all that proves is the vacuum is sucking back in the air that was expelled earlier from the header tank. I will continue to happen until completely cooled. That is quite normal and exactly what one would expect.

IMO though, it has nothing to do, however, with what pressure will be attained when the coolant inside the closed system reaches maximum expansion.

If the pressure is good, and assuming the expansion tank is the correct volume for the engine and partially filled to the right level, then only air will be expelled at 15 psi and the coolant around the cylinder heads will remain well below the boiling point at 15 psi (approx 135 deg C)

However, the lower the pressure the greater the opportunity for the very hot areas inside the engine to start internal local boiling and the creation of steam.

So if the pressure is sub standard due to some fault or other and steam has been generated locally causing internal pressures, that is when air PLUS coolant can be expelled.

Now it has been re-plumbed to make sure the coolant circulation prior the the stat opening is adequate, the situation should remain stable even when pulling 5.500 rpm on a hot day in timbukto, as it were.

From your descriptions, though, I think it would be prudent to measure the cooling system pressure at full coolant expansion - ie engine hot.

As I said, something caused the coolant to flood out from the pressure cap. On the other hand it could just have been a bit of crud on the sealing washer. A temporary glitch.

[adamnreeves]

Thanks for the Reply Ramon. I'll have to go back over your posts and re-read, lots of useful information and I thank you for that. Before I replaced the cap I did clean the top threads of the expansion tank and clean the rubber washer in the cap. Not sure how I can check the pressure in the system. The hoses are silicon and rock solid when engine running and up to temp.

[ramon alban]

Not sure how I can check the pressure in the system. The hoses are silicon and rock solid when engine running and up to temp.

Thats a good sign, so the coolant escaping issue must have been a glitch and the pressure cap is working OK presently.

On the other hand, if there were loads of air inside the system because it cant be burped or bled, then the rock hard pipes could suggest air pressure not water pressure, within.

There has to be a process available for your system that eliminates all air even though (if?) the expansion tank is below the highest point elsewhere.

Some systems use a valve at the highest point for this purpose, usually embedded in the top hose. Not pretty but, "needs must". Better to protect than to be elegant.




Regarding pressure testing, there are two issues.

1 Is the cap working? Does air/fluid escape at low temperature/pressure? If so. clean the seal/replace the cap.

2 Is the system breached somewhere else? A crude check would be to VERY CAREFULLY loosen the cap (not remove) whilst the engine is warm, using a thick cloth and see how much hissing and pissing occurs. If not very much, something might be wrong.

So one step further, do the same with engine hot and observe the result.

For a definitive test any garage could perform the test or one can beg, borrow, buy a pressure test kit.

Never had to revert to a definitive test myself, always used the crude method, but Google/Wiki knows how!

If that works out OK then the final thing is, how well does it hold pressure after the engine is cut, but before it starts cooling down.

Is any audible hissing due to air getting out or is it due to the resulting vacuum sucking air back in.

One is bad, the other is normal.

But how to tell the difference? Something for you to ponder!

[adamnreeves]

Hello Ramon,

I changed the coolant cap today, thought for the sake of a few quid, why not when the consequences are so costly. My expansion tank has no markings on it and its alloy so I measured the depth of the coolant to the bottom using my verniers, 75mm stone cold.

Went for a decent drive today, about 80 miles which included some quick blatting around lanes, crusing, traffic jams by the motor junction, diversions, etc. Used 3 gallons of Shell's Finest. Left my ECU logging on. Drive lasted for 83minutes temperature range 82c - 88c. 88c being when I was in a traffic jam. Just measured the coolant 3hrs after shutdown, guess the temperature is about 40c and measures 78mm. I'll re-measure when its stone cold tommorow but signs look good, luckily.

[adamnreeves]

Checked coolant level this morning. It was 45mm so no mystery changes anymore. So in summary changes made:

1. New cap
2. installed bleed hose from top of inlet manifold to top of expansion tank.