Spontaneous Overheating

[Intentional Wanderer]

The verdict - so far - from the guys at Falconworks in Tucson was...

... a bizarre thermostat failure. Turns out that this particular thermostat has a "safety" mechanism (that none of the mechanics, nor I, had ever seen). On the spring side of the thermostat, there is a small catch flange that acts to keep the thrermostat open fully (which it was when we pulled it) in case of overheating. A nice little mechanical wonder, if you ask me.

So, the thermostat shut (i.e. went bad)... the mechanism, sensing it was over its alloted temp range, popped back into the "fully open and locked" state. The only thing that could stop this from functioning properly would be if something jammed into the spring/mechanism to physically keep it closed.

...as to the stock Disco radiator, with 14 years and 128,000 miles, it looks almost brand new on the inside (well, what you could see after pulling the plug and using a borescope). We ran a flow test and it was 10% off of the factory new rates - Not bad for 14 years of gunk in the engine water spaces.

 

[SeaRubi]

Thanks for updating the thread, David. Glad to hear it was a simple fix.

cheers
-ike

 

[Intentional Wanderer]

Hmmm... I did have another "heating event", though this one not as bad...

While climbing the steepest grade in Southern Arizona, trying to pass slower traffic, while pulling along at less than 40 mph, with the A/C on... the Disco did start to move towards the hot side. I did do it again, without the A/C and had no problems...

I should be able to do that... shouldn't I? Is that too much to expect from the Discovery?

Not that this was "that bad", and I think that the new thermostat did help, but it does indicate that there may be something else at play... hmmm....

 

[muskyman]

I still say its your radiator, the only way to really see the state is to pull a tank.

 

[Intentional Wanderer]

I am now almost 100% convinced that it is a collapsing hose.

Yesterday, as we were heading up to Phoenix, the Disco started overheating...but never to the point of boiling over.

At one point, when I pulled into a gas station, the needle hovered around the H... that was the highest it got. I tried a fix that worked for an old Mustang that had a hose problem... turned it off.... waited 30 seconds... then cranked it again... VOILA... engine cooled off immediately.

Repeatedly on the trip back to Tucson, as the heat would go up, I would pull off and turn the engine off... wait a few seconds... then crank it back... poof... cooling again. I drove smoothly through Phoenix and it ran great - even on the cool side - from Anthem to the Salt River (where you start to climb out of the hellish bowl that Phoenix is in). No additional load = no heating problem.

I tried to hop out and get a look at the hoses to see if I could catch them in the act, but by the time the load had come off of the engine, the water pressure had lowered and the hoses all snapped back...

The lower one did feel a little mushy... and the top one definately - though I doubt it would be a problem with the top one as it is the outflow from the engine and should not be pressurized/vaccuumed (correct?)

As it was Easter weekend, and I don't have a spare bottom hose...and I have to be at work on Tuesday in Denver... the folks at the shop will get a chance to change them out.

Soooo.... any other ideas as to what would make the vehicle overheat - not to the point of boiling over... but run VERY warm... but only after putting a strenuous load on the engine... AND (a critical AND) reset itself each and every time you turned the engine off for 10 - 20 seconds... a fix that was tested probably 5-6 times and it worked 100%.

I really can't see how this is a radiator issue. Given that it fixesitself like that...and an inspection with a borescope looked fine... and the flow rate was only off 10% of factory new specs.

 

[RoverDude]

Did you check your viscous cooling fan when it was hot? Spin it cold then hot and see if you have measurable difference in resistance. When at load this could be the culprit that sends temp "over the top".
Question, did the gauge ever get into the red?

 

[Intentional Wanderer]

No, the only time it got into the red was the first time I encountered this a couple of weeks ago. The other times, I have caught it before it ever went "over the top".

On the trip down, I could see the guage change from slightly down from horizontal to straight horizontal... which it would stay at for several miles. If I then accellerated, it would move to the slightly above horizontal... slowing down would bring it back to horizontal... but never back to "cool". If I stopped and "reset" the system, it would go back to "cool" (or slightly less than horizontal) and then we replayed the scenario above...

 

[RoverDude]

Wandering near the middle indicator is fine. As long it settles just below (normal operating temp). The fact that the needle actually creeped into the red could be a problem. Keep an eye out for unusual pressurization of the cooling system. Those head gaskets absolutely hate to be overheated.

 

[Mike_rupp]

Thom, how many times have we seen disco owners that have cooling issues, replace damn near everything except the radiator and then realize that the radiator was the problem in the first place. For some reason unbeknownst to me, most Disco owners go into denial mode when it comes to radiators.

 

[Intentional Wanderer]

So, rather than just telling me it is a radiator issue, while none of the facts back that up... does no good.

Tell me HOW it is a radiator issue... how does a radiator act in a manner consistent with the symptoms... when a collapsing hose fits ALL of the symptoms... and the temporary fix.

I am not the first Discovery owner, but 30 years of owning cars that break in evey possible manner I can think of has taught me a few things.

This isn't my first rodeo... or overheating car....

For instance, a 1969 Mustang had a corroded spring on the lower hose. The spring disintegrated and not only caused the hose to not be able to hold itself open, but the part of the srping got into the water pump and fouled it as well.

I had a Chevy truck that blew a head gasket... milky oil.. milky coolant... I figured it out...

I had a Dodge truck that had a... oh... I don't know... radiator clog. It simply had too much crap built up from years of bad water... had it rodded out, worked fine... totally different set of symptoms... but, hey... what do I know...

My Triumph TR-6 had a bad water pump... as did my Jeep... which had a totally weird pump failure in that the impeller blades all disintegrated, but the hub of the pump kept pumping just enough water to make the engine run cool in all but the worst stop and go traffic. I actually drove that Jeep from Washington DC to Augusta, GA with essentially no water pump... (BTW, the same Jeep is sitting in my driveway... 5 years later, still runs like a top)

Let's not forget the half a dozen bad themostats that I have encounted along the way...

I may not be the first Discovery owner, but the first Discovery I have owned is not my first vehicle... unless somehow Land Rover has done something to make this vehicle act completely contrary to what all of the other vehicles I have owned... plus it also has to be contrary to all of the vehicles that have ever been serviced at Falconworks (a fairly reputable British car garage in Tucson) who ran flow tests and a borescope inspection.. and pronounced it "clean"...

Soooo....rather than just tell me that it is a radiator.. explain WHY you think that... Seriously, if there is something other than "gut feel", I would love to know.. as it may save me money in the future... but just saying "Discoveries all have bad radiators" isn't even close to an explanation. Dodge trucks have good ones, but that doesn't stop them from feeling the effects of 10 years of hard water.

 

[sven]

Your 14 year old radiator is clogged. It is no longer efficient at radiating heat. If you're in doubt get an IR temp thingy and point it certain areas on the rad. If you see cold spots, its clogged.

 

[Intentional Wanderer]

For my own education... can any of you radiator culprit theorists explain how that clears itself after only shutting the engine off for 10-20 seconds?

Clogged radiators are... clogged... 10 seconds does not an unclog make...

How does the flow test not show a clog? If you remember your fluid dynamics calculations from school, there is only so much coolant that can go through certain amounts of tubing.. if one is clogged, the others can't "take up the slack". Physics doesn't support it... unless the Brits have come up with a way... hmmm.....

Okay, so the flow rate was 10% less than new... let's say it is 10% clogged... I will buy that... well, 5% in the radiator and 5% in the water jacket of the engine... so... how can you take the symptoms... and the 5% - 10% reduction in flow... and arrive at "bad radiator"? I simply don't see how these add up.

Again, simply saying it is a bad radiator isn't enough. Tell me WHY... and more to the point... HOW... it can be a bad radiator.

This is all for the greater education of myself and others on the forum, the proof will all be known soon as I am taking it to the garage and not driving out until this is fixed... regardless of the cost. HOWEVER, I thought that starting with a $65 part might be a better way to go than a $650 part... but, that's probably just my silly ol' novice Discovery owner logic....

 

[sven]

if one is clogged, the others can't "take up the slack".

Right, And this is why the problem only happens while under loads, going up steep climbs, etc. Next time it overheats, turn on the heat at full blast. If the gauge goes down, the heater is "taking up the slack".

Most likely is clogged because of neglect.

 

[Intentional Wanderer]

Forgot to mention... tried the heater thing... to no avail... no effect... the heater worked like a charm... but no drop in engine temp...

again, this is not my first rodeo... or older car...

I don't discount the collective knowledge here.. but this just doesn't fit. I am wondering why you think it does... saying it does, doesn't make it so.

You can't take some of the symptoms... you have to take in ALL of the symptoms... and all of the fixes...

 

[rovertech]

David,

I have had clogged radiators cause intermittent overheat in both my old classic and my old disco. Not to mention the countless customer vehicles I have repaired. The term clogged is probably throwing you. Generally they become partially plugged. Mineral deposits from the water collect in the center of the radiator so you still will have some flow around it. This causes overheating to be intermittent and in some cases random. I know that doesn't make total sense but it has proven itself to be true in my experience. If you pull the radiator top plug (when cold obviously) and look into the radiator and see any white deposits chances are you have a whole lot of them in the center where you can't see. If you see any there at all I would pull the radiator and send it to a rad shop for a good cleaning/repair. The worst case scenario for you here is that the radiator wasn't 100% of your problem, but if it is even a little clogged it isn't helping either and needed to be fixed anyway.

My .02