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Hi all.

My 1999 4.6HSE 67k miles RR is overheating and losing coolant. Just did it 1st time today on a 40mph run towing a horse box, 24C outside temp, aircon on.

Knowing my luck its probably a cracked block.... but I was wondering if there is a definitive guide somewhere to diagnose it?

Something like a flow diagram or something?
Rather than randomly replacing radiators, thermostats etc.

Also, I know the importance of a 50-50 coolant mix, but a lot of people are asking what colour antifreeze - does this matter? Or is it just 'don't mix red and blue'?

Thanks in advance.
 

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OK, here's my checklist:-

1. Check for coolant in the oil i.e. mayo in the oil filler cap - sign of head gasket failure (or, god forbid, cracked head or block).

2. Check for oil in the coolant - brown slimy deposits in the coolant header tank - another sign of head gasket failure (or cracked head/block).

3. Check thermostat operation - remove and heat up in pan of water - should fully open close to boiling point. If not then cooling will not be efficient leading to overheat, increased pressure and coolant being blown out of the system.

4. Check viscous fan operation - should 'stiffen up' with increased temperature otherwise results can be as per 3 above.

5. Check condenser fan operation - if not operative then can lead to overheat (again, results as per 3 above) in hot ambient conditions when under load with aircon on.

6. Check radiator core for 'cold spots' indicating a blockage - may be cleared by back flushing otherwise new radiator required.

7. Check each hose joint in turn for leaks, including heater matrix 'O' ring - talthough his should not lead to overheat unless leaks are severe.

All the above, with exception of the thermostat, do not require any disassembly or random replacement of parts .......... until you find the fault.

As for the coolant, best to use an OAT antifreeze (usually red coloured) with an alloy engine.
 

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Thanks Garvin, presume if coolant is greeny-blue I should drain it completely and replace with OAT antifreeze?

No sign of oil in coolant or on filler cap (checked that when I bought it 3 weeks ago, still OK)

I'll check the other stuff tonight.
 

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Do you have a slow loss of coolant that caused overheating because the coolant was too low? Or did the engine overheat with a full supply of coolant? Two very different scenarios requiring different diagnostics. Slow loss means leaking or burning in the cylinders. You must find the leak or entertain possible engine block issues or head gasket issues. Overheating with full coolant means possibly thermostat or radiator or water pump issues or other coolant passage blockage issues. Nice diagnostic list from Garvin.

Coolant colors are not universal. Color does not indicate type of coolant. Read the label. It doesn't matter the color as long as it's an organic acid technology coolant (OAT). You don't want anything that says phosphates in the contents on the label. You want to see organic carboxylic acids (usually sodium 2-ethylhexanoate) in the contents. If you don't know what's in there now, and you want to be sure, then yeah, drain completely and refill. If you really want to be sure, drain and refill several times with pure distilled water to get all the old stuff out (running the engine between drains to circulate the water, then drain and refill with fresh 50/50 coolant mix a few times.

Brett
 

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Thanks Brett, it appears to be an overheat when full of coolant when pulling a horse trailer up a hill - so indicating thermostat or radiator. At least thats where I'll start!
 

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I have a '97 P38 HSE that had an overheating issue, which instantly stops your heart together with thoughts of head gasket, cracked block, slipped liner etc, etc, but it didn't seem to be the 'norm' that many write about here. I didn't have water in the oil, oil in the water, coolant vapour from the exhaust or any obvious sign of leaks. I did the sniff test which came out negative, checked the viscous, thermostat, water pump, took a thermal image of the rad, coolant pressure test and engine compression test, but still after around 15 - 20 minutes on idle the coolant erupted from the expansion tank. However, it never bubbled just shot out.

Garvin's post gave me hope and taught me not to jump to the worst and most expensive conclusions, and after inspecting every hose and joint I found a split hidden under the hose clip on the bypass hose. Not easy to see, no coolant under the car because I assume it simply evaporated on the hot engine, so it pays to be thorough.

Thanks Garvin!
IMG-20190328-WA0007.jpg
 

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No, all were fine. Now done over 200klm and no problems. Compression test was consistently good on all cylinders too.
 

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Contrary to popular belief, P38s do not eat head gaskets or crack blocks because they can, no more so than any other alloy engine. You won't get oil in the coolant or coolant in the oil with a blown head gasket because the coolant passages are at each end of the heads and the oilways are down the centre. A steam cleaned spark plug will show if coolant is getting into a cylinder but that will be accompanied by pressurising the cooling system and blowing the coolant out.

Overheating is caused by only two things, a lack of coolant or a lack of flow. If it spits the coolant out and then overheats due to the former, then you need to find out why it is losing coolant. If it is losing coolant it will overheat because there isn't enough left rather than overheating and then spitting the coolant out due to thermal expansion. A lack of flow can be a number of things but the two most common are a water pump with eroded impeller or a partially clogged radiator. A few years ago mine was running perfectly with no signs of any problems until I was towing a heavy trailer uphill and the gauge started to climb until the red light came on. Slowing down a bit and putting the heater on Max with the blowers on Max bought the gauge back down to normal. If it needed the additional capacity of the tiny, in comparison, radiator in the heater to keep it cool, then the big one up front wasn't doing a very good job. Replacing the radiator cured the problem for good.

As for coolant, the owners handbook for the GEMS (up to 98) says you should use Ethylene Glycol anti-freeze (the blue or green stuff), for the later Thor (99 onwards) it says to use OAT (the orange or red) although that is mostly due to OAT only being introduced during GEMS production and Ethylene Glycol was all that was available. As far as corrosion resistance and anti-freeze properties, there's not a lot to choose, the main difference being that Ethylene Glycol should be replaced every two years but OAT has a claimed life of up to 10 years. I'd rather treat it as a service item and replace every two years.
 

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Contrary to popular belief, P38s do not eat head gaskets or crack blocks because they can, no more so than any other alloy engine. You won't get oil in the coolant or coolant in the oil with a blown head gasket because the coolant passages are at each end of the heads and the oilways are down the centre. A steam cleaned spark plug will show if coolant is getting into a cylinder but that will be accompanied by pressurising the cooling system and blowing the coolant out.

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I don't agree with this, I had "mayonaise" in my sump because of a blown head gasket only 3 months ago.. And steam cleaned spark plugs
 

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Interesting, where had the gasket blown? Usually they will go between cylinders or out the side into the Vee or out the side of the block.
 

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Interesting, where had the gasket blown? Usually they will go between cylinders or out the side into the Vee or out the side of the block.
I had flanged liners installed in my block, but 2 of the liners dropped about 0.14mm, when standing in front of the car, the first cylinder on the right was one of the liners what dropped.

Head gasket was clearly blown at the dropped liners, but I couldn't see anything neer that oil feed, the white sludge was everywhere.

Engine ran so beautiful, and one morning she wasn't idling as nice anymore, and than she overheated one day...

I must say, I couldn't see any logic in it, because it used coolant, no white smoke, and the head gaskets where blown to the sides, gaskets looked fine at the coolant passages.

All fixed again.
 

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I'm not surprised you got coolant in the oil in that case, the gasket hadn't blown but was just leaking everywhere. I assume whoever fitted the liners refaced the block free of charge and I would have expected some sort of compensation for them getting it wrong (like them taking the engine out, doing the work and putting it back).
 

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I'm not surprised you got coolant in the oil in that case, the gasket hadn't blown but was just leaking everywhere. I assume whoever fitted the liners refaced the block free of charge and I would have expected some sort of compensation for them getting it wrong (like them taking the engine out, doing the work and putting it back).
Yep, nah, took the engine out myself, the did pay for the gaskets and stuff, they owned up to it.
 
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