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Discussion Starter #1
Pretty sure one or both of my head gaskets are gone but decided to test compression to help confirm it.
Symptoms: Constant overheating, coolant escaping from overflow reservoir
Fan clutch is working correctly, new water pump, Radiator flowing very well. No white smoke whatsoever, runs perfectly at all temps, just constantly in the red on the temp gauge. Checked with laser thermometer and engine IS overheating.

Compression test shows:
1-140psi
2-135
3-135
4-140
5-141
6-140
7-141
8-140
Does this rule out the head gasket? One mistake I made is that I removed the plugs one at a time and replaced each one after each cylinder was tested. Possibly masking a leak between cylinders but I feel that if it is leaking gasses in to the coolant the readings wouldnt be affected by the way I tested it.
 

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Nothin wrong with those results at all. It is not often you see results so close on an older rig. A leak down test would confirm a break into the coolant chamber. You have ruled out the temp sensor and obvious points. Have you had your coolant checked for exhaust gases? How many miles has your rig done?
 

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Discussion Starter #3
I have not had my coolant checked for exhaust gasses but I am guessing that would absolutely without a doubt confirm the head gasket assumption. I've seen the color-changing kit for about 60 bucks at a local auto parts store so I may try that if the results will be conclusive. Do you mean a pressure leakdown test where you pressurize the coolant and see if pressure escapes in to the cylinder? The truck has 158k miles on it
I will say that I'm not entirely convinced that it's a head gasket problem. The story goes like this, leaking radiator, patched it a million times, no overheating, still leaking, ran way too low on coolant one night and got it pretty **** hot, water pump weep hole started leaking, threw in a used radiator the next day, no leaks, but bad overheating, threw in new waterpump, no more leaks, still overheating, figured heads were trash so drove it all summer in the red. Never got any worse or any better. Aside from the possible over pressurization It just isnt really acting like a head gasket issue.
 

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A compression leak down test is a cylinder by cylinder compression test like you have done but with a wait period. A cylinder that leaks compression quickly will have either shot rings, valve sealing or head gasket issues. As you most likely have a shot head gasket this would tell you which cylinder to keep an eye on when you tear it down.
 

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I've been having similar problems - I would say the rad is probably blocked, the cores have very narrow waterways that can silt up badly and if someone's used a block sealer that makes it even worse.

threw in a used radiator the next day, no leaks, but bad overheating

You put in a used rad, overheating started. (Previous O/H was caused by leak/lowcoolant.) Did you check it/back flush it (although this isn't a reliable way of checking as a garden hose won't give sufficient flow - ask me how I know ;) ).

When the engine's hot, switch it off and feel the rad core all over, if its cold anywhere it's blocked. You might be able to get it rodded out (but not all rad places will do it) but they can flow check/recore it.

Good luck

Alastair
 

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1970-1995 Range Rover Classic
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How hot is hot? I had very similar numbers on my Classic and it was pressurizing the overflow tank, I did the heads and it fixed that issue. My truck never overheated but the factory gauge is useless. My radiator was certainly shot and got replaced at this time.
 

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Discussion Starter #7
I did flush the replacement used rad as best as i could with a garden hose, seemed to be flowing well. Either way I have also tried using the pre-overheat leaky rad just to see if it is a radiator issue and the vehicle acts exactly the same regardless of the radiator used. I'm pretty sure the temps that I have seen have been in the 240-260 range, too hot but not crazy hot.
 

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Is your ranngie on LPG? A converter can go bad and pressurise the cooling system with lpg. Probably not, but just a thought.
 

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vwzach182 said:
I did flush the replacement used rad as best as i could with a garden hose, seemed to be flowing well. Either way I have also tried using the pre-overheat leaky rad just to see if it is a radiator issue and the vehicle acts exactly the same regardless of the radiator used. I'm pretty sure the temps that I have seen have been in the 240-260 range, too hot but not crazy hot.
thats death temperature. I think anything past 195 is dangerous.
 

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do a search on this subject and you'll get tons of info. Ive tried different rads and found both were clogged. Also, flow across top viewed through filler hole will be good especially if its clogged. The most important symptom of head gasket problem is mysterious fluid loss, when its not coming out of overflow reservoir.
 

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Discussion Starter #11
Thanks guys for all the help! Installed a new radiator and this cured ALL of overheating and over pressurizing problems. I really toasted that motor almost daily all summer since I figured it was shot anyway and thank god it is still running beautifully! Thanks again!
 
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