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P38 strange overheating


sussex-landy
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Thought I would post this and see if anyone has seen it before.

My 2001 P38 4.0 has run fine for four years without having temperature issues. In December I did a full drain and refill with antifreeze 50/50 ready for the trip to the alps over christmas.

Had the usual heating issues due to air and cleared it then off we went 700 miles no issues didnt miss a beat.

I started it one day and the temp went up pretty fast to redline and the expansion tank was almost boiling. rad was very cool. turned it all off squeezed some hoses to make sure water was flowing started again and it sat in the middle no issue. Didnt give it an other thought.

On the way home did 300 miles stopped near luxembourg for petrol had no issues until this point, fired up straight onto the motorway and it hit redline, pulled over and checked and same as before cool rad and hot expansion tank like its bypassing the rad somehow. There does appear to be hoses to allow the rad to be bypassed so is there an issue with the bypass or a thrmostat, has the antifreeze dislodged something and is causing blockages, it was all pretty clean when I drained it.

The remaining journey home 400 miles was trouble free so thought I would pop this on here before I start going through the rave books.

Anyone got any experiencfe of this.

Thanks

Robert

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The thermostat is mechanical, works the same as in the TD5 with a bypass to aid warm up.

You should also check if the overflow pipe from the radiator to the tank is clear, as this is vital to ensure no air remains trapped in the radiator.

I have found on one of my P38a's that after a long run, it would sometimes build up pressure and dump coolant out of the expansion tank after shutting down. Typically when stopping on a motorway for fuel. If you miss this and don't top up, it can lead to overheating on the next run. As long as the level was good when I started, it would behave perfectly, even when towing a loaded cartrailer.

Filip

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yes thats exactly what seemed to happen, I suppose its a take off hoses clean out and replace if needed. strange thing is the bypass was the hot hose sending it back to the header tanking and dumping coolant so sounds like I should change the thermostat at the same time as well.

thanks

Robert

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Sometimes it can be a real pain to get all of the air pockets out. Try letting the truck idle for a while with the cap off and look for bubbles in the overflow bottle. Just be sure to do this experiment when the truck is cold.

If you get constant bubbles in the overflow tank you may have a head gasket issue

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  • 2 weeks later...

Well thought I would add an update to this saga which I thought was closed after running around for weeks at home with no issues, sadly not the case.

Just came down again to the alps through belgium, luxembourg and switzerland no issues sat in the middle all the way 12 hours 700 miles then started to go up pas de morgins and half way up woosh upto red instantly pulled over popped the bonnet and coolant is coming out the top heaters went cold again which sounds like air moving around on the mountains climbs.

Did the usual cooled down topped back up as i was carrying about 10 litres of water and antifreeze just in case and got lots of air out then went off again over the next few mountains on my way to my destination it did it three times but only when revving and going uphill.

Now I have spent the last five days running this on the flat and all sorts of angles with front upwards or downwards and can still feel air coming out, the bleed pipe flows freely and no bubble but does pass some air for time to time. Feeling the pipes (bypass, rad inlet and heater matrix in/out) I can feel air bubbles passing round. Do the usual when cold so no rad involved rev the nuts off it to get the coolant moving and let it settle more air comes out, once cold squueze the pipes which do pressurise ok and I can get more air out and sounds like a water swooshing sound where the heter matrix is so I suspect as everything does what it should on the flat just on tick over that air is in the high points on the heater matrix and although hot air is coming out (proved by running around in -5 with two windows open) I believe air is moving on the climbs and getting stuck in the rad inlet causing the bypass to be used and overheat at the same time it blocks the ubend in the heater outlet which I also notice goes cold.

So I am woring on the assumption ths is air blocks as this car performed great for over four years upto the day I drained and changed the antifreeze purely because I didnt want to mix them although now I wish I had, so I doubt it is head gaskets, rad issues, thermostats I know there are no blockages as what came out was clean and I have blown through the bleed pipe and also see water flowing freely out the tank end when revving up the engine and the cap is off when cold.

I am curious to know how a garage would do a drain and refill, if it was summer here I would shove a hose into the heater inlet and one on the outlout and pressure the air out that way but as its getting down to -8 I dont want to go to that extreme, I also read a lot of the same experience online and people do the tings they suspect it to the hoses, thermostat, header tank and amazingly days or weeks later its back so again i suspect air in heater matrix as they are so much higher than the heaader tank and the outlet is half way down the matrix itself. Who designed it wants shooting or why not put a leng of pipe into the engin bay with a central heating bleed nipple on tope and thumbscrew which I may be doing when I get back home if this continues.

I know I am rambling now but this is hair pulling out stuff and having gone through rave in detail and studdied the airflow and felt every pipe and different rpm its seriously pi?!£ed me off.

Robert

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I am really sure the issue is the heater matrix holding air as I can hear it wooshing when I squeeze the large inlet pipe in and out at home where I live its too noisy to hear it but here in the mountains its dead silent so I can hear the wooshing when cold and bulbbles moving when I turn it off, and when I rev the nuts off it some air comes through the matrix outlet (small amounts) but not the inlet (which does get hot) each time but its getting less and less. Just hammered it around the mountain I am on and not a blip and the hoses are starting to run free of air even when hot now so I may have blown most of it out but its taken close to 7 days on some steep angles to push the air out surely a garage will do something different when they refill the coolant. I find it hard to believe its much else as its sits fine on the motorway at 2000 rpm with heaters going for 700 miles then go up and down the mountains revving 3-4k and bang cold heaters and overheat. I would have thouhg head gasket issues use water up slowly or would be noticed on a 700 mile journey and more strangely its not missed a beat on the coolant or lost any for 4 years, not one top up until I did the drain and refill.

Robert

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  • 2 weeks later...

A brief update on progress as I read lots of people get this issue.

Mot of the air has gone but I am still able to squeeze a few bubbles here and there, mostly after its been sat on the flat revved a bit so it pushes the coolant around then left to cool. Doing it with the expansion tank cap on now to keep the pressure up.

I find once its cooling I can squeeze the large top hose then the expansion tank hose close to it and bubble can be felt coming up and out into the expansion tank. I know the bleed pipe is clear as I have cleared it and with the tank cap off there is a good flow of coolant through it when revving but I think the bubbles are too big and building up at the base near the thermostat so its not opening. The tell tale sign when driving is the heaters start blowing cold when they are up high and the window open so I know air has moved and the heating is reduced or stopped as its got stuck in the exit pipe in the bend and more than likely means its gone down the pipe to the thermostat.

I have taken all the plugs out and they all look normal no steam cleaned plugs or edges and as I have previously said this car ran sweet for four years before i did the drain and refill.

It will sit on the drive ticking over for hours with no overheat issue until I start going up and down the mountains and every time it overheats the heater will go cold first, so I jump out at this point (if its clear) turn it off and start squeezing hoses and air does come out.

I am not 100% sure if air is getting in as steam but as the plugs all look good and the oil is normal I am still going on assuming there is no head gasket issue and this is just annoying stubborn airlocks working their way around the system. I know the thermostat is working normally as I feel the flow of hot coolant into it once the engine gets to temp and the bypass hose cools down, having spent hours feeling the hoses and knowing the flow I am still sure its air.

Does anyone else have air in the rad top inlet hose once its cooled as I can still feel some in their and not sure if I should remove it and fill it as much as possible in that pipe although it only sounds like a little volume of air based on the swooshing noise I can hear when squeezing hoses from cold.

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  • 3 weeks later...

My discovery 2 had the same problem, but not as marked. My issue was slight water leaks from the heater pipes that go through the bulkhead leaking, and the throttle body heater leaking.

When the water leaks were fixed, and the system bled, the problem went away.

Mine was is running well but had the usual sick feeling I'd head gaskets liners etc etc.

Simple water leak. Bitch to find tho.

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  • 1 month later...

Good to know mine runs normal and just did 300 miles to Luxembourg and it overheated once then all the way home ok. I can always tell when it's going to do it as the heaters blow cold so I catch it before the temp gauge starts rising, always seams to be air locks but not ruling out early head gasket issues as the air seams to come from nowhere even when it's revved and runs clear. Always seams to be steamy out the back though which worries me but oil is normal no trace of water and all plugs are usual condition, no steam cleaning so still on the air lock assumption. Hasn't done it for a few weeks now.

Any idea how much work is involved to do head gaskets on these, I have rebuilt a few rover v8s in my hybrid but fancy doing the timing chain as its on 140k and the cover has a few Oil leaks around it and the oil is due a change so thought I might do head gaskets, valley gasket and timing chain and clean the sump out also gives me chance to check cam, bearing and heads to plan next steps.

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  • 2 weeks later...

Did you visibly see a leak, I have bypassed the heater matrix to rule it out and bled it to death until no air it present then I run it and the header tank goes down upto a 1cm and I can fell more air gurgling around which blocks it up sometimes and the temp goes up at which point I turn it off. When the heater was connected I used to feel the matrix and return pipe go cold and I knew air had moved but can find how the air is getting in and there are no leaks. I have checked the oil and still no cloudiness and all spark plugs are the same none look steam cleaned so doesn't look like heads, I kind of wish it was then I would just get on with doing them although its a bitch to do.

I could bypass the throttle housing as it doesn't do much just to make sure, I think it's just an in/out setup to heat it n cold weather.

I have to sort this as I like this car and it's Ben great for over for years but now it's randomly breaking down the wife is on my back to get rid of it for an audi 4x4 :(

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As a follow up I have found the issue and now konw why air is getting in. just removed all the plugs again after they looked good a few weeks ago and now one is pretty wet with water so its a head gasket change.

The oil showed no sign of water which didnt help.

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