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What to watch out for after over-heating


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I've managed to get my P38 up and running but am concerned about faults re-occurring. Can anyone give me some things to watch out for?

As a quick summary - the vehicle (4.6 HSE) overheated, the top hose had split dumping all the coolant. The previous owner had stripped one head down, then lost interest. It then sat for a year until I bought it. I stripped down the other head - cleaned everything up - checked heads for warp - and both appeared to be OK. I fitted new composite gaskets and rebuilt the engine, fitted new radiator and started it up.

It runs but has been smoking with white smoke after it warms up but I suspect that may be to water in the exhaust as the header pipes have been off for a year. Now that the coolant has settled it doesn't ssem to be going down (or it wasn't - but I just got a leak on a pipe).

It seems to work as normal with the top hose getting warm after it gets up to temp.

I wasn't sure if the pressure was normal, after running it was left a good few hours. I then removed the coolant cap and it hissed for a couple of seconds - is this normal after that long?

I can't drive it far at the moment but will run it again before I'm fininshed and take it for it's MOT but is there anything else I should look out for?

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Judging by the lack of replies, no-one is going to stick their neck out and tell you your engine is definitely OK or not. :ph34r:

If it's not using coolant, not boiling, not pressurising, not showing any of the other signs of head gasket failure and not sounding bad then all you can do is take it for a drive to get all the moisture out of the exhaust and blow the cobwebs out, and see if it passes the MOT.

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I know what you mean :rolleyes:

I'm not after a definite yes or no - just some tips really. Don't really want to book the MOT then overheat on the way after missing some signs. It's been a pretty big job for me, never done any work on a petrol car engine before, and never dealt with any overheating issues before so it's all new to me - to be honest I'm pretty impressed it runs at all!

Got a few small jobs left ready for MOT,

Finish Brake Pipe replacement

Fit Fan

Replace Leaking Powersteering hose

Sort rocker cover leak

Sort Windscreen washer jets (think one jet is snapped underneath) - pipes need connecting up

Fit front half of exhaust heat sheilds

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The problem is that you can't be sure it was the head gaskets as you didn't see the symptoms nor strip the engine in the first place.

If (hope there isn't) there is a liner / block problem, it probably won't reappear until the car has been up to temp and run under load for a while.. so its difficult to provide a definitive answer.

You know the symptoms: temp / high pressure in hoses / misfire etc so keep your fingers crossed and good luck!

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I had thought about a combustion test kit but they are more expensive than I expected! Anyone know a cheap way of doing this?

I'm just worried that when I book it in for the MOT it will be it's first proper run in over a year, normally I'd be wanting to take it very easy but at the same time I could do with giving it a 'good' run to clear it out a little!

MOT station is 8 miles away

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Coolant systems do pressurise as they get hot & its normal. The coolant expands as it gets hot.

Excessive pressure & ejecting water isn't (That doesn't include removing the cap when the engine is hot. Don't do it as you are very likely to get very hot/boiling water over yourself as the sudden release of pressure will allow the coolant to boil - hence the warnings on pressure caps)

If you don't have an unexplained water loss or water being blown out of the pressure cap you are unlikely to have a problem (at the moment!)

As to how long it should be after cooling down that you shouldn't get a slight hiss when you remove the cap I have no idea!

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Hi, I don't have water coming out of the expansion tanks or boiling over etc, I'm not 100% sure if I have water loss or not as I had to make up a temporary bodge pipe as a pipe was missing and this was dripping so I was losing some water anyway.

I've now replaced that pipe and providing there are no more leaks from around there will be able to monitor better if the level drops or not.

Thanks for the reply - it's closer to D-day now when I actually have to drive it for an MOT!

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Got a few small jobs left ready for MOT,

Finish Brake Pipe replacement

Fit Fan

Replace Leaking Powersteering hose

Sort rocker cover leak

Sort Windscreen washer jets (think one jet is snapped underneath) - pipes need connecting up

Fit front half of exhaust heat sheilds

Managed to get a bit further, brake pipes are now done, powersteering wasn't leaking at all it was the auto box cooler, I've fitted the fan, I've sorted the rocker cover leak, I've sorted the washer jets, I found a bulb out on the number plate and sorted.

Just got to:

Replace the plastic arch liners (need to buy some new plastic plug things!)

Replace the heat sheilds

Get a new Auto Box Radiator and fit it.

Still a bit worried about the whole overheating issue, now the brakes are sorted I took it for a 2 mile test drive. It all ran fine and never overheated. Power seems a bit 'all or nothing' but not sure if that is just a characteristic of a V8? Seems to have lots of poke though.

It's just that when it's started from cold it doesn't smoke at all, then after a few seconds once it starts to warm up, clouds of white smoke (steam) come out of the exhaust. Sitting on the drive at idle this doesn't seem to clear, when taking it for a drive it seems to clear straight away and doesn't return on idle. The exhaust was saturated with water inside before though some I'm hoping it's just water left in the exhaust but I presumed once it had cleared once it wouldn't return?

Coolant doesn't seem to be dropping, spark plugs look normal, it starts perfectly, it doesn't overheat.

Any thoughts?

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It's just that when it's started from cold it doesn't smoke at all, then after a few seconds once it starts to warm up, clouds of white smoke (steam) come out of the exhaust. Sitting on the drive at idle this doesn't seem to clear, when taking it for a drive it seems to clear straight away and doesn't return on idle. The exhaust was saturated with water inside before though some I'm hoping it's just water left in the exhaust but I presumed once it had cleared once it wouldn't return?

Any thoughts?

Probably condensation in the exhaust ……….. you get this with all large petrol engines. If left to idle you have to burn it out as steam, however, once on the move the higher revs force it out with the exhaust gases. You will get this on eavery cold start.

So far, it all sounds normal to me ……………

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Probably condensation in the exhaust ……….. you get this with all large petrol engines. If left to idle you have to burn it out as steam, however, once on the move the higher revs force it out with the exhaust gases. You will get this on eavery cold start.

So far, it all sounds normal to me ……………

Thanks for that, I've never had an engine this big so have nothing to compare with but it is rather a lot of steam at the moment, will keep an eye on it. If all goes well I'll be trying for an MOT ASAP.

^^^^^^^What he said.

Also the reason for exhausts on cars that only do short trips rotting quickly!

The exhaust isn't looking in the best condition and I'm sure my 4 mile trip to work won't help it either when I do get it running!

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Condensation in the zorst (and engine) can be quite considerable, when I had the 3.9 in the 109 I did a spate of short trips in the winter and when I pulled the rocker breather off it looked like mayonnaise :blink: I thought the head gasket had gone, but a thrash up and down the motorway cleared it out.

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  • 1 month later...

While you were working on the engine did you take the rad out or flush it through? Lots of threads on P38's mention blocked rads as the cause of a worrying overheating problem.

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This is a bit off the beaten track but I put a friends 306 back on the road after it had been standing for over a year, everytime it ran the exhaust pushed out lots of steam. There were no other signs of a blown head and it had been fine before being taken off the road. As a long shot I put a bottle of stuff for clearing water from petrol in the tank which produced an almost instant cure, for the ten quid it cost it's worth a try.

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