Thermostat bad?
 

Losing some coolant. Never overheats. Coolant hoses stay hard and tight overnight and overflow tank hold pressure. (Yes, I know it could be a head gasket but no signs of coolant in the oil)

Had the upper,,lower coolant hoses off and ran water through looking for blockage or something. Nothing.

Put it back together, refilled the coolant, did an initial coolant air purge. Went for a drive, got good cabin heat.

Oddly (to me), the lower rad hose is barely warm, upper hose is scalding hot.

Likely the thermostat has failed or should I not jump to conclusions?


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Thermostat failing won’t cause coolant loss. It will lead to overheating if it doesn’t open or slow engine heating if it’s stuck open. The best way to find a coolant leak is with a dye kit.

Also, post what your car and engine are so we can have more info. Or put it in your profile.

OP has ben chasing this leak for a couple of months...A UV dye kit has been recommended a few times. Has it been tried? If not I would...

I re-read your previous posts. You said you already swabbed your cylinders...But the excess pressure in your hoses tells me you probably have a head gasket problem. Have you tried a tester that tests for exhaust gasses in coolant? If not, please do so.

The fact that you also had a bad Aux fan (which you recently replaced) also leads me to this conclusion.

I suggest you find the leak, then worry about the thermostat..unless of course the car starts overheating.

What puzzles me a bit is that many people use these same arguments regarding engine coolant systems. When coolant heats up it expands so it's normal that coolant on a closed system is pressurised raising the boiling point. It's normal that the upper hose on a warming engine is hard. There is a 2 bar cap on the expansion tank for a reason. The coolant from the lower hose is cold (colder) if the radiator is doing its job or the thermostat is not yet open and there is no circulation thru radiator because the engine is still in warm up phase.

Test six monitor temp. Should hit 95 or whenever tstat design and stay there.

Stuck shut very rare


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An easy way to test...

Get a meat thermometer and stick in the center vent.
While driving around town at engine 1500-2000 rpm, the center vent should read 150F-160F or so, or it should be "uncormfortably hot" to your hand.

Make sure:
1. You turn the heat all the way up
2. Blower motor at 30-40% speed
3. ONLY center vent is selected (and the center air selecter is turned all the way to RED).

The only way I found a leak on mine was to park it for a few days. It passed pressure testing for leaks. An o-ring contracted when it cooled off. Check from underneath. Check for coolant running down the lower radiator hose. Use a mirror and light for tight places.

Pressure test cold can help


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How much coolant will it take without turning on the engine? I'll do a soapy bottle pressure test on mine. I'll use plain water for testing. Pump/drain the remaining green coolant the previous owner had in it. Blue coolant will go in.

The end is near and the news is bad….

I took the park plugs out of #5, #6 and fished a wire down in and both came back a bit wet with coolant. Decided to try the shade tree trick and put paper towels over #5 and #6 and turned the engine over. #5 definitely pushed out coolant but #6 nearly saturated the paper towel with coolant. Dammit.

This thing still drives, doesn’t overheat (yet), no coolant in the oil (yet).

I know it’s blasphemy but since it’s already had a head gasket (I did it 20k miles ago with no plans to do it again), is it ridiculous to think about throwing a can of stop leak at it?


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Yes - using stop leak is blasphemous

I think the failed aux fan did your engine in.

Replace the head gasket.. it should go quickly since it’s your second one..

Your exact circumstances forced me to do it twice also..that was 15k miles ago

Don’t know about the fan..as a head gasket survivor I constantly monitored the dash temp and unless the gauge or sensors were inaccurate it never once overheated after the gasket was replaced. I have no idea how long the fan was not functioning but I never threw a code or showed as non-functional on my reader until it failed this summer.

Thanks for the encouragement though.


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Gonna +1 on the have to replace. Did you use the stepped up thickness and any issues with following the exact bolt tightening sequence with new bolts. Lubrication state is a killer. Most get installed dry and any oil or coolant on the threads is a big problem. Some require lube to get the tension correct.

Sounded to me like “OLDMACTECH” knew what he was doing or enough of what he was doing to make it work..these engines take head gaskets pretty well.

But his failed Aux fan May have caused this..

I also have seen folks gouge the head on the locating dowel to cause this, but that is rare..

Plus one on using thicker gasket, but I don’t think that happened..

OP did you install time-serts the first time?

Thermostat bad?
 

I did you the thick gasket because the head had to be decked (not sure that’s the right term.)

Did use Timeserts and torque sequence.

Would not be at all surprised if I gouged the gasket as I seem to remember struggling with the weight of the head (bad Shoulder), and after all, I was I’m my driveway in December in GA.




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I think doing it in the driveway in reasonable weather is a great way to do it.

The clearance on an E53 X5 is such that it stays on its wheels the whole time for a head gasket.

The cylinder head with exhaust manifolds attached are damn heavy…I use an engine hoist to raise and lower the head for a head gasket.

You may have damaged the gasket, but the gouges I have seen previously were in the head itself and caused by the locating dowels.

Yes, I remember.
I’m 71 yrs old, think I’ve done my one and only.

However, for conversations sake, with no evidence of overheating, simply a matter of replacing the gasket or would the head need machining again?

Would the Timeserts have to be removed?


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I have a machinist (past retirement age, but still working) who I trust like a brother.

You likely would not need to have it machined - unless it is gouged - but every time I take a head off, I take it to the machinist to check for warpage and and a valve test. I also get a pristine mating surface. It runs me $0-300.

you do not need to remove time-serts...unless they failed and pulled. This is unlikely. If they have failed, I will loan you my 1050 Big-Sert kit.

Here's a thought...Maybe you find a kid who is showing some automotive aptitude (maybe from a local vocational school?) and have him/her help you...It will make the job easier. I've brought a relative along in a similar manner, and he ended up doing an BMW engine swap on one car, and a manual swap on another before going to school for automotive engineering.

You should do this head gasket...This is no reason to get rid of it.

I’ll commit to a firm maybe.


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Watched a couple of Youtubes, forgot what a pain it was (mostly getting the head and exhaust out.)


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I think you are a smart man to know your limits ;) The chances of doing a successful head gasket job get exponentially less each time you redo it especially of you are going to go back into it thinking something like the aux fan caused it.

The second HG job should be easier than the first. For one thing, the fasteners are likely easier to remove. For another, the person doing the HG job will know what to expect.

If OP did in fact gouge the head on the locating dowels (possible), maybe he'll try lowering the head with an engine hoist and lining up the holes with wooden dowels before dropping it on to the block.

I did my 2nd E53 head gasket in 18 months because a failed aux fan DID cause it. Both my clutch fan and aux fan failed. Neither one threw a code. I noticed it when the car was in traffic and the coolant temp gauge went off center towards the right. Once I was moving, coolant temps went back to normal. My kids drive the X5, I am sure this happened to them, the car overheated, and I never heard about it.

I replaced both fans and the head gasket and I have had no engine problems since...18 months, 15k miles.

OP - leave the exhaust manifold attached to the head and remove/replace the head with an engine hoist. Problem solved.

Thermostat bad?
 

Hah.

I still maintain the aux fan didn’t cause the head gasket to fail (the replacement anyway.) it never hasoverheated after my HG handiwork No idea why the first one failed but the symptoms ( high pressure in the overflow tank due to exhaust gas.) were the same.

I’m shopping for a replacement car but may have had it with the brand. Still in mourning currently. Perfectly good car with only 114k, ( I average 3500 mi. Per year)

I suspect the bolts nearest cyl 5 and 6 broke or broke loose. Of course those are the awkward ones to reach…..


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