I purchased a 2004 Land Rover Discovery II from a private party in southern kentucky on Friday. The test drive went great but when I began the 2.5 hour drive home, I didn’t make it 5 miles before the engine overheated. I was on the road side 10 different times bleeding the coolant system, refilling, and trying to make it a bit farther.
Background: The seller said they replaced the thermostat, rodded the radiator, and replaced the water pump earlier this year.
What is happening: Sometimes I make it 40 miles, sometimes 2 miles and the engine overheats. When opening the hood you can tell the coolant system is extremely over pressurized and spews large amounts of coolant out of the overflow cap. I have replaced the overflow cap and bleed screw to no avail. I finally got it to a mechanic and he tried a new thermostat but it overheated again. He’s been looking for a day now and can’t figure out what is causing the issue. Anyone have ideas as to what could cause these symptoms? I was thinking head gasket but the mechanic says he’s tested it three times and doesn’t believe that is it. I plan to pick it up on a trailer this evening to bring it home and attempt the fixes myself as I bought it as a spare/project vehicle. I just didn’t expect this big of a project to begin.

 

Rad is my bet.

These rads have plastic tops so no way that rad was disassembled and rodded out. Also there is the fact they knew it had an overheating problem leads me to believe they made that up

Overpressure comes from 2 basic problems
Head gasket allowing pressured gas into the coolant the shop can check for that with a test kit. - it will not necessarily discolor the oil.

Poor coolant flow is the other that generally in caused by:

• Clogged radiator
• Bad air flow
• Bad water pump
• Fan
• Possibly on Disco's a clogged heater core as it is an always flow design

The fact that the distance varies leads me to believe cooling system, I would start with a complete flush, with cold water. Read up on it here and make sure the mechanic does the heater core to.

Get yourself a bluetooth ODBII reader and monitor the actual temps with a cellphone.

 

How long was the test drive?

 

You do need to do the chemical test for blown head gasket, Oreilly has the trip available to use for free. 90% chance that is your problem. You can run the bottle cap 1 turn loose and it will not build pressure, but that will not change your pressurization problem. If there are bubbles in the coolant you definitely have a blown hg. You can disconnect top radiator hose from radiator, let water run out on the ground, put garden hose in radiator. See if it will idle without overheating with a steady flow of cold water.

 

I know you said you replaced the coolant reservoir cap, but before I dive into anything else I'd replace it again.

It's happily not common, but occasionally parts are bad out of the box. For $15, I would hate for you to spend a lot of time and a lot of money diving into other possible causes when the problem may be a defective coolant reservoir cap. The symptoms indicate that as the problem. If that is wrong, you can always return the cap.

 

About 15-20 minutes. Took it up to 60+ mph and couldn’t sense anything wrong.

 

I will have the vehicle home tomorrow to dive in a little further. I will try a new cap because, I agree, $15 would be worth potentially avoiding larger issues. The mechanic ran a slew of tests and said “signs are pointing to a blown head gasket but I can’t prove that’s definitely it.” I will try the radiator garden hose test and see how it does. The vehicle cools fine when idling. It isn’t until it is driven that it begins to overheat and seemingly build too much pressure in the coolant system. Would it overheat while idling if it were a head gasket issue?

 

@Mjfleck10 It could idle fine if the gasket is just starting to let go BUT it is pretty unlikely. It is pressure that creates the problem rather than RPM and compression should be pretty stable

 

I spent the better part of 3-4 weeks in my spare time replacing the head gaskets. I got down to the heads and admittedly the gaskets seemed ok. No cylinders or heads seemed ‘pressure cleaned’ so I put in new gaskets and built it back up. That makes for new head gaskets, new expansion tank cap, new hose from tank to throttle body (broke in the tear down), and the car fax says new water pump as of last March. I flushed the radiator by putting a garden hose in the top and it flowed freely out the bottom so I don’t believe anything is clogged there. I’m dreading the reality of a potentially cracked block but am holding out hope that I can still pin it on something else. Any ideas?

 

If the block was cracked you would have steam cleaned piston(s) and coolant in the oil.

The heater core could be gummed up, try flushing it.
And the fan clutch could be worn out.
Both will cause overheating.