Overheating def - help please

[JST]

fitted with electric engine fan on manual override on and thermostate controlled switch, fitted in bottom hose.

symptons as below:

Took landy for a drive yesterday to tip for the first time with thermostat in.

Temp climbed very gradually but then seemed to get rather high (top of white area). No fans had cut in so I turned it on. Temp didn't rise but didn't seem to drop.

Got home and lifted bonnet. Top hose was very hot but bottom hose still quite cool and expansion tank cool as well. Fan was certainly heaving air through.

I would naturally expect a temp variation between top and bottom hose as that is what rad is meant to do but this seemed extreme. You could feel the top of rad as hot but soon on the bottom half of rad cold.

The thermostat must have opened as hot into top hose so that can't be causing issue. It just seems the water is not flowing around the system correctly as I would expect if top hose so hot, (too hot to hold for longer than a couple of seconds) bottom hose should be warmer.

When first tested, top hose also very solid. When opened expansion tank lid, there did seem to be a lot of pressure. Wonder if lid not working properly (think you are meant to change them after several years. Mine still the same one I got with it).

To me it seemed too extreme difference and top hose did seem too hot I feel so think it was overheating the engine. The hot air from heater was also very hot which is unlike a defender!

Obviously it wasn't a very hot day and in fact I was out while raining so overheating shouldn’t be a problem at all. Also I was generally moving all the time at 30/40mph as town was quiet.

the above is an extract from an email from Dan to me (he doesnt have internet access at work)

some further historyis that when he last ran it without a thermostat the temp guage bearly moved above the min setting and heater ran cold. and that was a 100mile journey at 60mph.

any thoughts/suggestions?

[Les Henson]

I would suggest an air trap restricting thw flow.

If it was me I would let the engine cool significantly, drain it, then start the engine and gradually re-fill while it's ticking over. Otherwise, you might find that as the engine cools down the water level suddenly drops.

It's worth mentioning that the top hose being hot doesn't mean it's full of hot water - it could be full of hot air.

Les.

[bishbosh]

What about flow through the radiator?

If its clogged up with gunk you'd get similar simptoms I would think.

Maybe a backflush is in order?

[Happyoldgit]

An airlock is worth investigating but before you start digging too deep are you sure the thermostat is ok? I've had brand new ones that have turned out to be sticky or non functional in the past.

[v8bertha]

fitted with electric engine fan on manual override on and thermostate controlled switch, fitted in bottom hose.

symptons as below:

Just a thought... Shouldn't the thermostatic switch be fitted in the top hose, where the water is at it's hottest?

D

[DSN]

Hi there.

Managed to get online now but thanks James for getting things started.

Re the thermostat, I thought I had tested this one in a pan before fitting but thinking about it, I don't think I had tested this one. Of course as the top hose and top part of rad hot, I had assumed open as hot water. Could be hot air I guess.

Engine had been driven from SW to Midlands without thermostat when engine first fitted and no problems (ran very cold I think going by heat, or lack of, from heater). The changes since then are cut bottom hose to fit the thermoswitch (X-eng system, recommended in bottom hose so know temp as water returns to engine after been through rad), refill and run for while without thermostat then quickly stick thermostat in.

My old TD did get an air block once when I stuck a thermostat in before refilling but the temp shot up very quickly. I now tend to refill without thermostat so hopefully clear any air blocks then stick thermostat in. I learnt from a friend that thermostat should have a small bleed hole to avoid air blocks. I have noticed some don't have anything so I do tend to drill a little hole in the large plate so even when closed, a tiny bit of water can keep getting past.

For filling, I simply filled from top of rad till full. Fitted the large bolt then topped up at expansion tank. Does this seem good route?

Well cheers for any info. Might whip the thermostat out and test in pan as a quick easy job. Guess rad flush might be next route to check that bit.

Thanks for now.

[GBMUD]

For filling, I simply filled from top of rad till full. Fitted the large bolt then topped up at expansion tank. Does this seem good route?

Well cheers for any info. Might whip the thermostat out and test in pan as a quick easy job.

I always fill my 200Tdi Defender from the expansion bottle with the top rad plug out. That way it fills from the bottom and drives any air out. When the radiator overflows I give the top hose a couple of pumps by hand, wait for the water to start running out of the top plug again and then re-fit the plug. Doing this with the engine running may also help.

Testing the 'stat is always good news! Mine sticks about half open. OK most of the time but gets hot when towing the caravan on the motorway.

Chris

[Mo Murphy]

Engine had been driven from SW to Midlands without thermostat when engine first fitted and no problems (ran very cold I think going by heat, or lack of, from heater).

If the heater matrix is air locked and full of air, you'll get no heat from the heater but the engine can be as hot as you like

Mo

[JST]

Mo - heater matrix was cold on journey sw to midlands and no thermostat.

then hot (very hot) when the thermostat had been changed.

i think there was an intial air block in the heater matrix, thats now gone, but on fitting sensor and thermostat theres now an air lock in the top hose or the rad is blocked.

Dan if after removing the thermostat and refilliing as discribed here theres no joy try running water from hose pipe through the rad and see if that clears it. or not how much water goes in the top of the rad on refill etc.

[western]

Take the radiator off the vehicle & flush it through from the bottom hose connectio [i.e. reverse flush]. it must be a airlock.

[JST]

sorted it yet Dan?

[DSN]

I managed to whip the thermostat out last night and test in pan of water along with a couple of others I had.

The one that was in the engine opened earliest so don't think there is any problem there.

FI, although it is Disco 200tdi, I have opted to run an 82deg rather than 88deg thermostat.

I am now thinking rad is the most likely cause. When I drove from SW to Midlands, it was without thermostat and about 5degC outside temp so the engine probably didn't rely much on rad flow anyway.

Think I will go for a thorough flushing of the rad with the neighbours hose soon (no ban for us thankfully!) and see what comes out/flows through.

An additional query, can anyone explain why the new thermostats I have recently bought don't have a small disc at the bottom whereas older versions for landies do have this additional disc with a spring attached? Just wondering what it is for.

Well I will keep you informed.

Cheers,

[Guest weeble]

Are you sure its overheating or are you just believing the guage.

If the engine was out of a 200 tdi Discovery and it is now in a Defender, you will need to re calibrate the guage as the senders and guage are different from each other. The only way to get a proper reading is to fit a Defender tdi guage and sender.

Hope this helps.

[JST]

good point weeble and prob a contributer although i feel the bottom hose would have been a tad warmer and the top hose not rock hard which were other symptons.

[Guest weeble]

I agree about the bottom hose being warmer. But the question is why was it running without a thermostatt in the first place?.

If it was overheating with a large amount of pressure you would assume it would be boiling.

The pressure could be the result of compression getting into the water system.

[DSN]

I agree about the bottom hose being warmer. But the question is why was it running without a thermostatt in the first place?.

If it was overheating with a large amount of pressure you would assume it would be boiling.

The pressure could be the result of compression getting into the water system.

Weeble, the engine was without a thermostat as we fitted the engine in January but did not manage to get an electric fan fitted by the time I had to drive home. To avoid any problems, we simply removed the thermostat and assumed the cold weather and no thermostat would avoid over heating issues.

Certainly didn't see any heat issues all the way from SW to Midlands.

The rad is actually a 300tdi rad but this shouldn't cause any issues. We unfortunately didn't flush the rad before fitting as externally it looks very good condition but I guess internally it might not be. Hopefully a hosing through might highlight something.

Surely if there is a blockage in rad, the pressure in top hose would be due to water pump pushing water to rad but restriction slowing the flow through?

I will keep you informed with my progress.

Cheers,

[Guest weeble]

Dan.

Personally I would think if the radiator was that obstructed the engine would boil over. I would be interested to know if by flushing the radiator it cures the problem. Not wishing doom and gloom, but by what you describe, personally I think you have a head gasket problem or a cracked head.

[white90]

with the engine running hold the rad hose and rev the engine if you feel the hose buldge with the revs

the head gasket may be an issue,

I'd think the rad could be blocked

or the gauge/sender are unmatched and are misleading you

[Les Henson]

I would have thought that if the top hose was solid then the bottom one would be too as the pressure would equalise through the rad regardless of if it's water or hot air. Does the cooling system pressurise straight away? If you leave the filler cap off and start the engine- does water get pushed out of the expansion tank?

Or does it overheta very quickly? These are syptoms of compression gases getting into the cooling system.

The 200TDi engine does have a bit of a history of head gasket failure on No4 cylinder. Don't know about cracked heads, I understand that the heads on this engine are quite tough? You could do a cylinder leak test on your engine - there's a chemical you can buy that changes colour if fuel/exhaust gases are present in the coolant.

Les.

[western]

Recently my cylinder head was replaced due to internal cracks between oil/water ways, not to surprising after 1/4 million miles from new. cooling system wasn't pressurising like yours is though.

[Guest WALFY]

Dan

Sorry to give bad news. I had the same prob a few weeks ago and it turned out to be a knack head, but could easily of been a blown gasket.

Hope all goes well

[Les Brock]

Sounds very similar to all the problems I had with mine...how could I forget

Ended up having the head skimmed and been fine ever since..

[DSN]

Well to update you all, I ran the engine again last night without the thermostat in and tested as White90 had said. Sure enough the top hose does bulge with the revs.

I also had a look in the expansion tank when running and along with water moving, there did seem to be little air bubbles coming up and seemed to be linked with the amount of revs etc.

Coolant appears to be very clean still so don't believe oil is mixing in. Also the oil is looking clean on dipstick as well.

It is therefore looking like gases getting into coolant system.

So what is the feeling? Just a head gasket or head issue as well?

Obviously looking like head will come off. If so, what should I be looking for? If obvious issue with gasket then is it likely to only be that or could head also have problem?

Also, any comments on sourcing a head gasket? Only genuine or are others okay?

Any info gratefully received. I suspect work will probably happen in a couple of weeks time. Will probably look at doing it at my mate's workshop anyway as he is more expert in these things and has the contacts locally if it needs to go for head work etc.

Well thought I would keep you informed. Obviously not great news.

Cheers for all the assistance so far.

[Les Henson]

A steady stream of bubbles is a sure sign that compression gases are getting into the cooling system.

Although if you have just filled the system, then you might get this for a short while afterwards.

You could do a leak test and this would confirm exhaust/fuel in the coolant.

I would change the head gasket and get the head skimmed - this is common practice when replacing the gasket on an alloy head. You could also get a crack test if you think it's really necessary, but personally I leave that until changing the head gasket/skim has not cured the problem.

Having said that, if this has been doing it for a while, then I would expect a head gasket leak to get worse fairly quickly, as the gasket breaks up.

Take the head off and see what you can see - then take it from there.

Les.

[JST]

Les,

we dont know the engine history so are unsure if it has been doing if for a while. i think its a new occurance. Dan note that it may do it after refilling initially.

If the rad was still blocking flow could that still lead to the top pipe expanding with engine revs? (water pump casuing it?) and bubbles in tank from air still in system coming out?