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Another P38 overheating......


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A friends P38 4.0 with LPG overheating......header tank empty......leaks apparent around the LPG mixer gubbins and a larger leak at (or close to) the bottom of air filter to inlet manifold connection gubbins (sorry about the description, but Im no expert...) Refilled the coolant (+/- 5 litres!!) and run engine on idle. some occasional bubbles apparent, but not continuous. Oil is clean in rocker cover. Engine came up to working temp and stayed there.??? Not driven it anywhere yet or called anyone out to it. Dont think its a head gasket problem as I know the LPG system uses the Hot coolant to vaporise the gas.....any suggestions? (apart from the obvious....) When engine was stopped, coolant "flowed" onto rocker cover and exhaust heat sheild producing clouds of steam.......cant see exactly where its coming from.

Can any one point me towards a garage with P38 knowledge in Frodsham/cheshire area...?

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If you lucky, it was just the leaks you detected that slowly drained the coolant. When the level is low enough, you'll get a build up of steam and pressure, bad cooling and eventually overheating and loss of coolant through the valve on the expansion cap.

Sort the leaks, keep a VERY close eye on both the temperature gauge and coolant level, but try to drive it. Also check the bleeding hose (small pipe from the top of the radiator to the expansion tank). It needs to be clear for the system to bleed properly.

You're likely to get some erratic behavior at first while the systems tries to get rid of the air that is now trapped inside. The air bubbles will cause the temperature to spike occasionally, but should return almost instantly.

Good luck,


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Just a thought. Where have the water pipes to the vaporiser been connected? Mine were connected into the heater pipes at the rear of the r/h rocker cover with T pieces. I had a leak on one of them which caused water to run along the rocker cover and drip onto the heat shield just as you describe. It turned out the T pieces were made of plastic and one had cracked by over tightening the hose clip.

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I have been working through a similar overheating issue and I would advise firstly assuming leaks are sorted, fill the header tank to full when its cold rev it from cold and release a few times feel the bypass pipe, main inlet pipe and eater matrix in/out pipes for water flow and air bubbles which you can feel gurggling around. once its getting warm turn it off as the P38 is pressurised so yes coolant will come back out the top if you let it get too warm then turn it off. Once cool squeeze the large inlet hose (on and off) and see if air comes out the header tank again, keep repeating until no more air but that wont be the last of it.

I then started doing this with the cap on the header tank and getting it to running temp to make sure the rad was getting hot at the top from time to time as it mixes the cold and hot and stops using the bypass hose, then you can feel the bypass getting hot which means the thermostat is closed and on bypass which starts warming at this point rev it and feel the bypass as any air is abvious and the same with the heater matrix outlet pipe. Squeeze the bypass pipe 50 which restricts the water for a few seconds and rev it as it pushes the water faster and carriers the air down to the thermostat where it should rise upto the header tank inlet pipe which is marginally higher and about 30 mins of doing this I let it cool again then squeeze the large inlet pipe to get more air out. Its taken me about four days of doing this and I am finally getting to the point where I cant feel anymore air. And as for the bleed pipe yes check its clear but unfortunately its so thin if a large enough airlock hits it and builds it doesnt cope and hence the rad is bypassed and you get boiling water. By the way you can see if the bleed pipe is blockage free by revving it when cold (no thermostat open) squueze the bypass a little and it forces coolant down the bleed pipe and you see a steady stream coming out the header tank. Once the cap is on the header tank and all running hot if you feel the bleed pipe it will get hot then go cool again as the rad is used or bypassed..

Once its cold if you squeeze the big pipe on and off and its quiet enough can you hear water sloshng around, if you can there is air in there somewhere as water alone wont slosh. I could hear it in the inlet hose to the rad and around the heater matrix area so I kept doing it.

This has been my experience with my car which hadnt missed a beat since i decided to drain, refill and antifreeze it late December but worth doing to make sure there is no air before looking at expensive parts.

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