P38 overheating but why?

Apologies for my maiden post being a plea for help, and a long one!

I have searched this excellent site and others to try and get a reasonably definitive answer to my P38 problem and so determine my next course of action but remain confused. If I can summarise whats happening and hope that some wise and more experienced P38 owner can say "sadly yes, it is probably your head gasket" then I can stop piddling about replacing everything else.

Mine is a May 2000 RR 4.0se auto with 74k on the clock and believed original. I bought it about 8 months ago with a reasonable service history.

About 2 months ago, driving modestly on a local trip, having just that minute said to my wife how pleased I was with the car (typical) the temperature gauge went into the red and the header tank looked fit to explode. No water loss, no muck in the oil. I ran it again locally next few days and no problem. Then taking it for a service about 10 miles away from home, I `wellied it` away from the traffic lights and boom, same thing happened, red area temp, solid top hose and header tank ready to burst.

The mechanic ran it during the week, fast, slow, ticking over for ages and nothing happened, temp needle dead centre, no water loss, no emulsified oil. no smoke, running well.

He changed the thermostat and viscous fan, everything seemed ok! Last week, driving along a motorway after about 35 miles, I noticed the temperature creep up, nearly red, then dropped down to normal. A few minutes later, up again then down............ then finally up! No water loss etc, same as before. AA said the bottom hose was cold and therefore the newly replaced thermostat was at fault?

Relayed home and then out the next day and gauge up and down after 25 minutes driving at night. Finally hit red when I arrived home.

Today, I put some Kseal in (2 pots), took it out and within 3 miles, bang, up into red, quicker than ever and stayed there. System really pressurized, top hose solid, no water loss, oil fine, possibly exhaust smell in header tank? But have I just read too much? Certainly beginning to wish I hadnt read about Kseal!!!!

Started up just now, ran for 20 minutes, revved up and right down left on idle, no problem! Warmed up really quick as usual but stayed there. Bottom of radiator cold compared to top. Water seemingly circulating to header, then I burnt myself checking, serves me right!

So! May I ask for some guidance please? Head gasket, thermostat again? Blocked radiator even though I flushed the systenm first time round? What do you think. I would like to build up trust with the old girl again!

Many thanks in anticipation, Robin.

your rad may be blocked. suggest you disconnect top and bottom hoses and run hose pipe through. also i would get compression test done to see if the gasket has gone.

I agree with brutus. the rads on p38s get clogged up in time and flushing out is not always successful. if the rad has cold spots on it then its a good pointer that the hot water is not getting through that part of the rad. the k seal probably finally blocked any small gaps left in the cores .

Thanks guys, a very good pointer.

Would a blocked radiator give all the symptoms described and pressurize the system?

I drained the system and flushed through after the first hiccup, it seemed to flow through pretty quick then, I can see how the Kseal might have blocked things though.

The heater has been working brilliantly and I did wonder if fiddling with that started things of?

Is a compression test easily done by any garage or does it really have to be a specialist?

Regards, Robin.

yes a blocked rad will cook the engine in no time, as for compression test any local mot garage will have the tool to do the job. 30min top

Take the spark plugs out and check them for signs of a washed look. If theres a fault internally then 1 plug will be clean while the others will be a tan colour, make sure you do this after the engine has been warmed up properly then allowed to cool. If you do this after starting from cold all the plugs will be black and give you a false "reading"

The reason i ask you to do this is because I suspect liner slip, if one of the middle plugs are clean then its definately liner slip and not the head gaskets as there is no water jacket between the cylinders. If one of the end plugs are clean then it could be either a head gasket fault or a slipped liner.

The fact that it is seriously over pressurised kind of points towards a head gasket or cylinder liner problem

Thanks again.

I will take a look at the plugs tomorrow.

I had read of `slipped liners` but thought this only happened to earlier models hence me buying a facelift model from 2000 to hopefully safeguard against this.

The car runs perfectly apart from the temperature and pressure build up, the oil looks clean and fresh. The top hose is still `squeezable` but is pretty turgid when the gauge is in the red zone.

Oh, I hope its not a liner!!!

Cheers, Robin.

is the internal heater working and hot?
i would start by ensuring there are no air locks. as said above flush rad with hose pipe, maybe even get some rad flush product from local motor factor. also flush heater matrix at the bulkhead in the engine bay. i usually fill it from the hose that comes from the water pump too when i drain down then refill with water/antifreeze 50/50 mix, bout 5 or 6 litres of anti!!

i'm assuming you have read all the posts on overheating on this forum so you will be familiar with suggestions on filling etc?

Hello.

Yup, the heater has been working brilliantly, really hot after a while.

I will read the posts on filling and air locks but the problem began before any flushing or coolant levels were tampered with. Prior to the first over-heat a few months ago the car had been running perfectly and been to France and back, although, come to think of it, it did use some water then (about 500ml a week)! It then seemed to stop and thats when the problems started!!! Very odd, loses less water when the heater is in use but overheats?

Your thoughts are much appreciated, Robin.

Also a thing to check is the little pipe that runs from the header tank to the top of the radiator, make sure water is coming out. It wont be much but some should.

If not take it off at both ends and blow out and also blow out were it connects onto.

I've heard of people replacing their engine before because this pipe was blocked, and it will give you the same symptons as a blow head gasket.

Podge Abersoch said:

Also a thing to check is the little pipe that runs from the header tank to the top of the radiator, make sure water is coming out. It wont be much but some should.

If not take it off at both ends and blow out and also blow out were it connects onto.

I've heard of people replacing their engine before because this pipe was blocked, and it will give you the same symptons as a blow head gasket.

Click to expand...

the connection mentioned here to the expansion tank on mine was blocked, i had to use a drill bit and carefully tease the crap out, don't connect it to a drill tho or you'll hurt yrself!!!

Good advice, thanks.

I have taken the pipe to the header tank and blown through. Certainly a dribble at tick-over but more of a spurt with revs, so hopefully enough.

Awake early this morning, saddened at the possibility of a slipped liner in a car I was just getting to know and like, albeit my 5th RR. So today holds flushing the radiator, checking the colour of the plugs and trying to be optimistic. Its the transient nature of the symptoms and the general well-running of the car that confuses me.
(Excuse the language, I have a medical background!!!!!!!!!!!)

Again, many thanks, Robin.

whilst you flush the rad leave the top hose connected to the engine and remove the thermostat and reverse flush the engine with hose as well. if the water ways are blocked it clear them as well. it all worth doin to try a nd elimanate the problem. and buy the way does the viscous fan work correctly?

The viscous fan was replaced along with the thermostat 5 weeks ago. This was considered to be the original problem. It seemed to cure things but only for a few weeks, then the temperature fluctuations began and have worsened dramatically since the Kseal. Although running late yesterday seemed ok again, only I didnt drive, just ran it for 15 minutes.

Cheers, Robin.

The is a possiblity the thermostat could be faulty so i would test this in i pan of water on the stove?

Thank you.

This was the AA`s diagnosis, so I will whip it off whilst preparing to flush the radiator. I has anticipated a new one being good for longer than a few weeks!!

always test thermostats before fitting - as a duff one can be catastrophic.

if you dont know how to test the stat, hang it over the kettle with piece of string {dont stick it in water} boil kettle and watch for stat to open before the kettle has boiled. stats open at around 90degress will say so on top of stat.

Afternoon all.

I haven't gotten on too well today with my list of tasks.

Nipped to Halfords to buy some radiator flush and new anti-freeze, then took out drain plug from radiator and a disappointing amount of fluid drained out with seemingly very little Kseal in it. I put a hose pipe initially in the header tank but none came through to drain out and simply overflowed. So I took off the top hose and tried to flush from there but to no effect, it backed up and out.

There is some drainage from the bottom of the rad, but a dribble only, very slow. Slower than I remember it when I drained initially a few weeks ago.

Cant check the plugs as I cant heat the engine up.

Am I missing something in my process? Should the water charge through or simply dribble as is, or does this suggest a blockage, exacerbated by the Kseal? Is there anything else I can do?
Run the motor, hit it, advertise it on Ebay?

Seriously though, many thanks, Robin.

it is still blocked. the next step woukd be to use a home jet wash which has a low power out put. i brought a cheap power devil 1, it crap at big jobs but ive flushed a rad before with it. borrow one from someone before getting anover rad. or you could take ya rad to people who do rads and they will do a flow test for you. but they will tell you it blocked anyway, tho they might be able to help you out. also you need the RED antifreeze for alloy engines and NOT the blue.