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I've owned my 90 for the past 170K miles. It's got close to 200K and the engine hasn't been opened yet. She's been a daily driver her whole life so maybe that's why she's faired well so far, who knows. My conundrum is I'm planning to send her to CO and meet her there, primarily for the Land Rover Rally in Ouray in July. She's not overheating but if the ambient temps are in the high 90's she can get into the low 200's at highway speeds. Her coolant res will occasionally need some topping up, so I'm assuming she's probably losing some coolant through the head gasket somewhere. Part of me feels things will be okay, but another part of me feels like maybe I should put her down and do the HGs before the trip. At 200K though, she's probably also due for some attention on the bottom end as well. Is it ill-advised at this stage only addressing the top end? If so, I'm a bit concerned I may not have time to address everything the right way the first time.
 

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Do you think it would be a wise move to include which engine your 90 has in your opening post?
 
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I’m with theOneTen. Check first. And not a bad idea at all to treat a known symptom prior to bottom end. Frankly, other than the rear bolt on a gems, it is super easy to do a HG insitu, but I’d pull and put on stand to do bottom end seals and bearing check which has minimal to do with cooling loss. I live in CO, and it WILL put strain on your engine/cooling. So make sure it’s in good order, but don’t assume it’s the engine— could be radiator if you haven’t flushed it or even hose leak that dries before you drip but makes you lose pressure. I’d do a system pressure test around 18psi on your coolant, a block test using aforementioned fluid, and see what those two tell first. And if its been a while, get your radiator cleaned. If you have never done that, consider doing it.

I’ve been plagued with heating issues at altitude and believe I have a lot of expeience— not due to typical situations, but because I have an off-road trailer/pop-up that I have to tow along due to some medical issues involving needing batteries at altitude…so pulling weight up steep trails and passes over 9000’ in rarified air (which cools way less) has been a struggle on 3.5/3.9/4.0/4.6 engines and I’ve done them all.
 

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... and if you're really into the diagnosis mindset, I'd do the pressure test, coolant exhaust test, and also put some water-compatible UV dye into the radiator so you can see WHERE and HOW the coolant loss is occurring. The UV dye is my #1 diagnostic tool - all checks done at night and you can see some great things including whether there is a head gasket leak as you'd see a bit of dye at the tip of the exhaust. Also great for seeing if you have a leaky radiator fitting, or if the radiator itself has a tiny pinhole leak that you might not see with the engine cold.

Definitely diagnose before you start throwing parts at the problem.... ESPECIALLY if it's a compound problem.
 

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I had about 170k miles on my 3.9 when I decided to replace with a Turner reman. When I pulled the old engine down, the biggest issue was a VERY worn timing set. The cylinders looked good, but the nylon timing gear was allowing enough slack in the chain I am surprised it did not jump a tooth. The worn timing set really robs you of power as the cam timing is way off. So if the compression check is good, you may want to look at installing a new timing set.

Lots of ideas here, but check easy stuff first - look at the plugs. If one or two are crusty, probably burning coolant. If it is burning a lot of coolant, the plug could also look very clean (steam cleaned). Look at the cap gasket. If the cap is old, get a new one (they are cheap). I had my crusty radiator cleaned, which made it leak, so I am now sporting an Alisport one (which works so well I have to run a muff in the winter to get ANY heat in the truck).
 

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Discussion Starter · #9 ·
I had about 170k miles on my 3.9 when I decided to replace with a Turner reman. When I pulled the old engine down, the biggest issue was a VERY worn timing set. The cylinders looked good, but the nylon timing gear was allowing enough slack in the chain I am surprised it did not jump a tooth. The worn timing set really robs you of power as the cam timing is way off. So if the compression check is good, you may want to look at installing a new timing set.

Lots of ideas here, but check easy stuff first - look at the plugs. If one or two are crusty, probably burning coolant. If it is burning a lot of coolant, the plug could also look very clean (steam cleaned). Look at the cap gasket. If the cap is old, get a new one (they are cheap). I had my crusty radiator cleaned, which made it leak, so I am now sporting an Alisport one (which works so well I have to run a muff in the winter to get ANY heat in the truck).
Thanks, good stuff.
 
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