I've got a 2003 Disco II that was overheating when under a load. It would idle fine with no overheating, but it would overheat as soon as you started driving. This belongs to a buddy of mine who is a decent shade-tree mechanic. He said that the problem started after the coolant reservoir "exploded". He replaced the reservoir, radiator, water pump, and thermostat. It still overheated. He used an engine exhaust fluid detector (which turns yellow if exhaust gasses are present in coolant) and it did not change colors.

I'm a professional mechanic but mostly work on diesel equipment (Skidsteers, mini-excavators, etc). So he asked if I'd have a look at it.

I used a vacuum coolant purge on it and the coolant system would draw down to 24" mercury and hold it there for five minutes without the needle moving, so I felt that the system should be leak-free. And (as I used the vacuum purge) it should not have any way to get a bubble in the system. But the engine would still overheat. I used a different type of exhaust gas detector than his and it did not show any exhaust gas in the system. Then I tested it AFTER it had overheated and the fluid did change to yellow... so blown head gasket I figured. Also, the line from the intake heater plate (where it connects to the reservoir) would bubble.

Just got the heads off and I can't see any evidence of the head gasket leaking. In my experience, I have usually been able to see where the gasket had leaked. But these gaskets both look okay. And the heads/cylinders look fine too... none looked to have been "steam-cleaned".

Have any of you seen these Bosch V8's blow a head gasket, but leave no evidence? I hate to put this thing back together and still have the problem. I'm gonna take the heads to a head shop and have them checked (and cleaned, valves seated, etc) before putting the engine back together. Any advice would be much appreciated. Thanks in advance!

Lee

 

I’m pretty sure you’d see evidence of a HG leak when you remove the heads. When the reservoir blew up did the engine overheat or did he shut it off right away? I think you need to figure out why it’s overheating. Is the new t-stat bad? I’m not sure if it’s possible to connect the coolant lines wrong. It’s odd that it runs cool at idle but overheats as soon as he drives it. In my experience idling at a standstill is one of the worst cases for overheating.

 

Unfortunately, the symptoms you describe could be caused by a cracked cylinder liner in the block. You should probably pressure test it before putting it back together.

https://landroverforums.com/forum/di...-plates-51616/

 

Harvlr... thanks for the reply. Yes, it did overheat when the reservoir blew. And he (as well as I at first) was unaware of the problem with the temp gauge being way slow on these trucks. After it overheated on me a couple of times I researched it on this forum and found out about the gauge problem. I was then watching the temp in OBD Fusion (Bluetooth app on iPad) and was startled by how hot it was getting while the gauge was still midway. It would be almost to 230 before the gauge would begin to climb above normal.

 

Extinct, thanks for the quick reply. Interesting video! I looked at the top of the cylinder liners and they appear okay, but I presume it might not be that obvious. I didn't mention it before, but I never saw any evidence of coolant in the oil. In my experience, they usually will get either coolant in the combustion chamber and/or in the oil. All the cylinders have a considerable amount of carbon build-up on the pistons and combustion chambers. And the oil is black. My buddy really needs to change his plugs and oil more often.

Is it possible for the head to warp and let combustion gasses get by only on the compression stroke?

 

You can check the heads for flatness. Its pretty rare but the liners have been known to crack and only open under high temperatures.

 

@Troy_Less The only thing I can aad is I had a a passenger side head gasket let go, it was a hairline crack to the cooling channel. My disco never broke 196 even with crack (I caught it early). But the driver side head was so far out that it could not be trued but that gasket held just fine go figure.

My understanding is that a small block crack may not be big enough to let water into the oil but will rapidly heat the coolant and cause rapid over pressure of the cooling system

 

Extinct, thanks for the advice. I'll probably have the machine shop check the heads, but in my experience heads that leak has always left a mark on the gasket and/or the heads (or block). The cylinder sleeves look okay visually... they don't appear to have dropped at all. I looked at the video of the pressure test kit, but they didn't show a view of where the water was coming out of the block. I searched on people who used the kit and sounded like the jury was still out on its effectiveness. Also, it seems that it would be better to check the block when it was warm... which would be difficult with the heads off and it in the frame.

I will probably recommend to Rover's owner that we find another engine. But my curiosity really wants to find out how the coolant is getting combustion gas in it.

Like I said earlier... I really hate to have the heads decked, add new gaskets, and then put it back together only to have the same problem.

 

Thanks for the advice, everybody. I talked to a friend who has run a large Honda repair shop for thirty years. He says he's seen 2 or 3 over years that had combustion gas leaking into the coolant, but no sign of it in the head gaskets, no steam-cleaning, and no cracks. Considering he's done hundreds (maybe thousands) of head gaskets during his career, seems like it's unlikely that the combustion gas is coming from the head gaskets. I'm currently waiting on a good straight edge so I can check the engine block's head surfaces for deviations. I feel like if a liner had a crack, I'd see at least some steam-cleaning in cylinders; but maybe not. The guy that owns the Disco will probably decide what to do once I check the heads and block. I'll update this post then.

 

Driver Side

Driver Side

Pax Side

Gaskets Top

Gaskets Bottom

Driver Side