QuestionQUESTION: I have a +- '96 discovery series 1 with the 3.9 V8I engine.
The engine starts and idles very smoothly, and drives well, but when towing it overheats and loses power quite dramatically, now off the road with a burst header tank.
The water pump sounds very smooth (long screwdriver test) and there is no water in oil or oil in water so gaskets are probably fine. How do I test if the water circulation is sufficient? I can replace the termostat but do not want to replace the very expensive pump without knowing if it is a problem.
Anything else I should be looking at?
ANSWER: Your symptoms may suggest a failing head gasket, or a badly clogged radiator. You might try testing the air in the expansion tank with an exhaust gas analyser. Combustion gases would be a sure sign of internal failure in the motor. That's what I'd lean toward, esp with the burst header tank
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QUESTION: The header tank (plastic) burst as a result of the coolant boiling. I do not think the radiator is clogged as the engine cools down very quickly on a downhill, literally 30 seconds makes the difference between coming over the top of a hill with the needle almost on red, and temp dropping to normal (just below halfway)
I forgot to mention that soon after startup from cold there is a once-off sound of gushing water within the pipes, suspect the interior heater gets a rush of water, any idea what this might mean, perhaps thermostat lifting off its seating?
ANSWER: The additional information tilts the diagnosis more toward an internal failure withing the motor - a liner failure in the block or a head gasket failure. Most of these failures nowadays turn out to be liners, requiring a new short block engine
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QUESTION: Thanx for the input.I can understand how the gasket could do it, combustion pressure forcing through to the coolant channels, but a liner? If you mean cylinder liner how do these fail and how does it mean I need a whole new engine? Is there an easy way of diagnosing without special equipment? I was thinking if I pull a heavy load with the header cap off and the coolant sprays when cold, it would mean gasket for sure? Should I try that?
AnswerThe steel liners move in the aluminum block, breaking the combustion seal. That happens when they are loosened up after an initial overheat incident. YOu can only diagnose that with totl engine teardown. That's what your symptoms point to, based on my experience doing this 20+ years with LR v8s
