Hello Friends
2003 Discovery 2, 4.6L V8 - just crossed 200k today. Wee.
The engine was rebuilt about 3k miles ago by qande.com with tophat liners and everything was replaced, for example head gaskets.

It's been weeks of sleuthing and I need new points of view.

I have a coolant system leak.
1) Going through about a half pint a week. I don't put a lot of miles on it most days.
2) I have a 180' thermostat, and run an ODB reader to Torque Pro. I am not overheating.
3) There are no coolant drips under the truck, ever.
4) There does not appear to be any mayonnaise in the oil whatsoever.
5) Pressure test - at 20p.s.i. it drops down maybe 1/2 pound per 10 minutes.
6) CO2 test on the coolant system does NOT show exhaust gas in the system.
- ran it for 25-30 minutes
7) UV - dye in the system 3 days ago, drove it 100 miles today. I cannot find any drips anywhere.
- I have been under every goddamned inch of that truck with a UV flashlight at night
- Took an eyedropper, put coolant places to "see if I would see" - I am confident I would see drips, I am not confident I would see evaporated former drips.
8) There is a small piece under the throttle body (the heater plate) that often leaks and drips coolant onto the engine where it evaporates, I replaced this 4 weeks ago.

HERE IS WHAT I *THINK* I NEED:
A) A precise list of places where coolant leaks have been discovered/are plausible that would slowly drip onto a place that was hot and it would evaporate.
B) Tips for troubleshooting, for example "this product smells coolant" or whatever. I really thought the dye was gonna work but it doesn't leave stains.
C) Any other explanation. For example: too much air in the system pushing it out the overflow that only happens at highway speeds when I'm running hotter, and it's dry by the time I'm parked. I'm willing to admit the possibility I didn't get 100% of the bubbles out sufficiently when I changed the thermostat several months ago, but I really think I'd be past that by now with 600 miles and a gallon in since then.

 

Pull the plugs, look for one that is much whiter than the others.

Put it on pressure test overnight with the plugs out. Borescope the cylinders, look for one with coolant in it.

Coolant does not evaporate, not at all. Not below about 400 degrees.

Any fault codes? 02's working ok?

 

I had this on my TD5 D2. It was leaking out of the pipes as they went into the block and was hidden by other ancilliaries. But all the damage was underneath the pipes. It was suspected that 'a previous owner' had moved the pipes so they were not as obvious.

But it does sound as if you have covered a lot.

What have you done with the radiator? Have you checked that? Damage within the fins that would 'evaporate' in use may be one thing to consider.

Good Luck, sounds like you're trying hard on this one.

 

well if its not a cracked block maybe this shop will warranty the work sounds like a head gasket

 

I'm willing to try the spark-plug test, someone else also suggested it might be a blown head gasket -
Is it possible for a HG to be blown/leaking coolant into the cylinders and have a
1) Normal CO2 exhaust test on the coolant at the reservoir
2) No mayonnaise/milkshake on the dipstick or at the oil cap.
3) No fault codes.
4) Normal output O2 sensors at idle (real-time monitoring on Foxwell).
5) "Seemingly" normal engine despite a ****ty cylinder that has water in it?
- coil pack went a month ago and I knew instantly I had dropped a cylinder, and as soon as I swapped new ones it sounded great again.

Is there any other way of testing this before I start doing that, any sensor output etc?
- e.g. oxygen sensor outputs under load

Agememnon asked about radiators - I haven't done a thing with them except shine a light and not see any leaks.

Given how recently the engine was rebuilt, it seems more likely (more hopefully on my part, really) that it's incompletely tightened difficult to see lines. Nnnngghh I hope so.

 

Have you checked the throttle heater plate?
Its underneath the throttle and is a common leak, not the easiest to see if you aren't looking for it, and the leaks don't usually hit the ground.
Look under the throttle, there are two small water lines that connect to a small plate, if you see any crud on the plate it's leaking.
New throttle heater plate is under $30, but they fail often enough that people in higher temp areas just bypass the heater plate.

 

Xanthro - Thanks - throttle heater plate is what I meant when I wrote front cover, I've edited it. Replaced it when I pulled the top off to get to the coil packs.
It actually looked like it was leaking, so I really thought I had it nailed. Didn't though.

 

Your edit says
'' There is a small piece to the top right of the throttle body (the heater plate) that often leaks and drips coolant onto the engine where it evaporates, I replaced this 4 weeks ago.''

The throttle heater plate is under the throttle body, so the ''top right of the throttle body' 'is throwing me off. I can't imagine what you'd be referring to being the top right of the throttle body.

 

You're right, I meant top right relative to engine while looking at it "on the throttle body," instead I said "of" and should have been "under" the throttle body which would have been more accurate and less idiotic as stated. Re-edited.

Confirm, I replaced the throttle heater plate under the throttle body.


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Have you replaced the cap on the coolant reservoir? They can sometimes develop a fault such that the system no longer pressurises, and the hot liquid will simply overflow out of the tank while you're driving.