3C mk2 - overheating but can`t find the reason

[tobias]

Hi forum,

we`ve overhauled our JCB 3C mk2 engine 7 years ago, new pistons, new liners, reworked the whole head etc. It has worked supreme since then, very very good. Last year we´ve worked for hours at 30 °C outside, no problem with overheating at all.

Now it is overheating and the cooling systems gets pressurized and 1-2 liters coolant is gone thorugh the rad cap (no water in the oil or vice versa). The radiator itself is three years old. Obviously the head gasket is gone, and today we removed the head. But we couldn`t find the reason why the overheating has started. We checked the following:

- bores for the coolant
- core plugs
- water pump ( we will put in a new one, because now it is all disambled)
- head seems ok, there was coolant in all the bores
- we changed the thermostat from a 74 degree ot a 82 degree a few weeks ago, but that didn`t help. but maybe the old one was the problem? even if it worked for the last years.

What else should we check? I don`t want to put it all back together and then have the same problems a few hours later. Maybe someone can give us some hints, i would appreciate it.

And what time does the engine takes to have a water temperature around 90 degrees with not much of a load? 30 minutes or faster? What is your experience?

Thanks!
Tobias

[Jeremy Rowland]

Tobias, you mentioned that you changed the thermostat, does that correspond with the overheating issue? I was wondering if the new thermostat was faulty and causing the issue? The only other thing I could think of and why it would happen after this time I could not say but while the head is off have you checked the liner protrusion? Has one of the liners sunk a little causing combustion gases to enter the cooling system?
I am no expert on the JCB machines but is there a hydraulic oil cooler in front of the radiator, if so is that clogged with muck?
Just a few ideas to try and help you.

Jeremy

[essexpete]

I would check the rad core is clean. I had trouble years ago with a rad that looked clean but when I took it off it was choked with fine dust. With the oil cooler in place difficult to clean.

[gecko.cx]

The most common failure with thermostats I've seen is not complete, but partial failure. This is where the the thermostat only open part way and doesn't let enough flow through to keep the engine cool.

Try dropping the thermostat in a saucepan of water and heating it up.
This will tell you: a/ if it is totally failed. b/ how far it is opening.

[tobias]

Hi all,

thank you very much. We`ve tested the old and new thermostat (74°C and 82°C), both are working fine. The radiator is quite new and clean, we don`t have an oil cooler (manual gear).

I saw a black spot on the head gasket around the liner ring, maybe there is something wrong. Now i have to find out on how to measure the protrusion, i am not sure if we did it 8 years ago.

I will keep you updated.

[Jeremy Rowland]

Hi all,

thank you very much. We`ve tested the old and new thermostat (74°C and 82°C), both are working fine. The radiator is quite new and clean, we don`t have an oil cooler (manual gear).

I saw a black spot on the head gasket around the liner ring, maybe there is something wrong. Now i have to find out on how to measure the protrusion, i am not sure if we did it 8 years ago.

I will keep you updated.

Tobias there is a thread about this in this section if you look for it, the liner protrusion is fairly critical.

Jeremy

[tobias]

Hi, thanks for the feedback. We`ve checked the standing height already and they where all ok. It was 0,1 mm or around 0.004 °. But he checked it without pressure on the liners with that special tool. Could that be a problem?

We could see a 2-3 cm long part of the head gasket around the liners that was bad. So the head gasket was definitely gone. We now think about putting it all togehter, but i am not quite sure since the reason for the bad head gasket is unclear.

[gecko.cx]

- head seems ok, there was coolant in all the bores

"all the bores" is very unusual unless it was just a bit draining in when you loosened the head.

I think it would be worth getting the head crack tested - particularly if you can't find anything else wrong.

[Jeremy Rowland]

Tobias, it does sound like the head gasket had gone, Fred (Fowlerman) would have a better understanding of what the liner protrusion on these engines should be, I have never rebuilt one so I have no experience of setting one up. Like Ian says it may be worth the time and trouble to get the cylinder head pressure tested while it is off the machine, let us know how you get on.

Jeremy

[essexpete]

If you get the head tested it would also be worth checking that it does not need a skim.