Shouldn't be boiling should it?

[Dannyroger]

G'day

My 98 D1 LPG V8 runs fine (although I reckon a bit down on power since I had it LPG tuned) and reads a constant midway on the OEM temp gauge - except for a recent 90 minute highway run in 40 ambience with AC when it neared the top.

On that day, when I stopped to get fuel, boiling coolant escaped from the pressure cap on the expansion tank. I let it cool down, topped up a litre, and was on my way - no problem.

Today, lower ambient, shorter run - temp gauge normal, no overflow but I could hear the coolant boiling in the top radiator hose.

So I'm just hoping someone can confirm, before I start mucking around and breaking things I should never touch, that it's running too hot and the expansion tank cap is no good.
After that, I may also have to look at instead/as well - thermostat, air in cooling system, dirty or blocked radiator, and engine tune.

Does all this sound right?

many thanks

Tim

[TriPolar]

My guess is that you have a blockage somewhere and the water is not circulating. Thermostat or water pump.

[Dannyroger]

looking at some previous posts sounds like working out a overheating issue can be seriously tricky and time consuming. Thinking a good start might be to run it without the thermostat and see if any difference.
Seeing as the temp gauge reads normal, I guess that must be buggered too ...

[bee utey]

If it's making bubbling noises and pushing out coolant with the temp gauge within reasonable operating limits, chanced are a stuffed head gasket or worse still a stuffed engine block. These things crack easily and combustion gas gets out behind the liners through a crack in the block. Removing the thermostat may keep it alive for a bit longer but you risk freezing up the gas converter on cool mornings without a thermostat. A better mod is to fit an extra tee and brass nipple to allow gases to enter your header tank without pushing out the coolant.

http://www.aulro.com/afvb/attachment.php?attachmentid=37315&d=1310206925

Or start saving your pennies for a new motor.

[Dannyroger]

Thanks Bee-Utey
Not the diagnosis I was looking for!
So if this is the case, then most likely the expansion cap, temp gauge and thermostat are all operating as they should.
So how do I confirm that it is a cracked block, slipped liner or head gasket? (I can't see any bubbles in expansion tank when running nor any sign of water in the oil) I don't have facilities but a compression test at the local servo?
And can't quite work out your photo - the T goes into the existing 8mm return line and off the tee a new hose to the new fitting in the top of the expansion tank?
And the biggest question of all - what if I do nothing about it at all?

[bee utey]

Thanks Bee-Utey
Not the diagnosis I was looking for!
So if this is the case, then most likely the expansion cap, temp gauge and thermostat are all operating as they should.
So how do I confirm that it is a cracked block, slipped liner or head gasket? (I can't see any bubbles in expansion tank when running nor any sign of water in the oil) I don't have facilities but a compression test at the local servo?
And can't quite work out your photo - the T goes into the existing 8mm return line and off the tee a new hose to the new fitting in the top of the expansion tank?
And the biggest question of all - what if I do nothing about it at all?

You won't see bubbles in the expansion tank at idle, the problem occurs as combustion pressure builds up under load.

You won't see water in the oil until your problem becomes much bigger, small amounts of water will evaporate from hot oil.

A compression tester won't show a small head gasket leak, only a complete failure or a valve or ring problem.

Your working out of the pic is correct, the tee allows bubbles that normally collect under the radiator filler bung to migrate uphill to the expansion tank and vent without pushing out coolant.

If you do nothing other than checking and filling the coolant before each trip your engine will probably survive until one day you blow out enough coolant to cook the engine and destroy it.

[Dannyroger]

You are THE guru.
Many thanks for all your wisdom.

[gazby]

It may not be your problem, but I have seen a collapsing (inward) bottom radiator hose cause a similar problem in a V8 Ford Fairlane, not familiar with Disco V8 installation but maybe worth a look if the hose is old or oil soaked, looks ok at idle/low RPM but on a rev or prolonged high RPM closes and restricts flow.

[Boony73]

If you do a search of the site the biggest culprits for over heating in a Disco V8 are the viscous coupling, radiator, head gasket and the thermostat. Expansion caps do fail and if you have no idea on how old it is then it can be a cheap quick fix, same for the viscous coupling more expensive but they have a finite service life as well. Just recently I have similar symptoms, a bit more severe and it turned out to be a head gasket and a radiator.

[Dannyroger]

So what I really need to work out is if my Disco IS overheating or whether it's over-pressurising. I think the latter, cos I've not seen steam even when the cap spewed over.

[Grahame Roberts]

I had a similar problem when I acquired my 97 V8. I was advised to have the radiator overhauled but before I arranged that, I had a boil over. Luckily I did not drive any more upon seeing the steam. After the radiator was refurbished and a new thermostat fitted, I had no more problems until the auxiliary fan stopped working in Darwin. Since I have had that replaced it runs very cool. However, as soon as I had the first warning, I fitted an electronic overheating sensor and this had saved me in Darwin. DO NOT rely on the OEM gauge as they are never reliable.

[Tombie]

looking at some previous posts sounds like working out a overheating issue can be seriously tricky and time consuming. Thinking a good start might be to run it without the thermostat and see if any difference.
Seeing as the temp gauge reads normal, I guess that must be buggered too ...


Good grief NO!!!!!

Never run any modern engine without a thermostat...

They do more for cooling than just open and close!

[loanrangie]

It can overheat even more without a thermostat by not controlling the flow thru the rad, flows too fast and it wont exchange the heat.

[bee utey]

It can overheat even more without a thermostat by not controlling the flow thru the rad, flows too fast and it wont exchange the heat.

Now there's a myth I though had died with the decommissioning of the Ark. A water pump is not exactly a jet turbine. Why do you think that high flow (large aperture) thermostats were invented? I've used them and they work well.

The most important reason to keep a thermostat is to get the temperature quickly to a point where the ECU doesn't do the equivalent of putting full choke on. Some thermostats are vital to retain for proper cooling but that is because they block the bypass flow when the engine is hot. A D2 thermostat is of that type. The D1 V8 bypass flow is small as it only goes via the heater core. Then as I mentioned before you need a thermostat on a vehicle that has LPG or needs an operational heater.

[clubagreenie]

BU,

Guess what happens to a D2 when incompetence installs the thermostat the wrong way round.

[Dannyroger]

So my disco may or may not be overheating, may or may not have a cracked block or blown head gasket, may or may not need work on its cooling system so i figure the starting point logically needs to be being sure that it is actually overheating. There seems to be general agreement the OEM temp gauge is not to be relied on so an aftermarket temp gauge would seem to be the go. Suggestions? Engine Watchdog appeals cos it doesn't involve mods to the cooling system but I'm spending $149 before I even start ...

[ss_0001]

Try replacing the thermostat and do a coolant flush at the same time. A relatively inexpensive start to try and solve the problem...

[Grahame Roberts]

Get the watchdog anyway as it will save you in the long run.

[SouthOz]

+1 for the watchdog.

Dave