hmmm I am Baffled

[jrmc47]

Hi all ...have a problem that I think i have the answer to.....but I would like to see if anyone comes up with the same as me
at present I have an overheating problem..has overheated slightly since being rebuilt...4m40t full reco. hot tanked ..decked ...rebored new internals except crank...15 lb boost ...EGT's never go north of 350c since injector pump reset to original specs by pump reconditioner...new head ..new water pump..new thermostat...new heater core ....new alloy radiator 16 inch thermo fan .... new hoses ..no leaks

runs at between 80 and 90 celsius as long as you drive it with a feather on the loud pedal...put it under pressure and it goes up over 100c ...pushes about a litre or so of coolant into the overflow...DOES NOT RETURN IT TO THE RADIATOR when its stone motherlesss cold..as a matter of fact the cooling system is still under pressure when i crack the cap when its cold

my thoughts are that I either have a cracked head or head gasket has been breached between the cylinder and water jacket...the only thing that puzzles me is the pressure in the cooling system when cold
cheers to anyone that chimes in with their opinion....

[brw0513]

Is it possible you have an air pocket in your cooling system some where?

Have you tried idling, from dead cold, with the radiator cap off?

Is it blowing white smoke at all?

[jrmc47]

I have used a cooling system filler bucket thingo ...ran the engine to operating temp with it on and let the engine cool overnight and then put cap on...same problem doesnt blow bubbles....no white smoke ...just a puff on a decent rev

[jrmc47]

I have used a cooling system filler bucket thingo ...ran the engine to operating temp with it on and let the engine cool overnight and then put cap on...same problem doesnt blow bubbles....no white smoke ...just a puff of black on a decent rev

[Keithyv]

You mention new everything including the kitchen sink but not new radiator cap?
Maybe worth a look if not new?

[erad]

You mention a 16" thermo fan. My memory tells me that this is not standard fitment. It could be that the fan thermostat is set too high and the thermo fan is not cutting in or at least it is cutting in too late. Also, do you have the original viscous fan coupling fitted. If so, is it working properly? You should hear the thermo fan cutting in and out if it is working.

As for the residual pressure even when cold, this is more concerning to me. It sounds as it you do have a leak from the engine into the cooling system. You can get a test done to detect the presence of combustion gases in the cooling water - maybe this should be done and if no gas is detected you can at least eliminate that from the equation.

[jrmc47]

You mention a 16" thermo fan. My memory tells me that this is not standard fitment. It could be that the fan thermostat is set too high and the thermo fan is not cutting in or at least it is cutting in too late. Also, do you have the original viscous fan coupling fitted. If so, is it working properly? You should hear the thermo fan cutting in and out if it is working.

As for the residual pressure even when cold, this is more concerning to me. It sounds as it you do have a leak from the engine into the cooling system. You can get a test done to detect the presence of combustion gases in the cooling water - maybe this should be done and if no gas is detected you can at least eliminate that from the equation.

ahhh yes ...will look at that tomorrow thankyou

[Tomalophicon]

Who did the head bolts up? Can you confirm the correct procedure was followed?
I recently did my first 4m40t head so I'm no expert but there is a strict tightening and loosening and tightening procedure to follow.
Tom.

[disco stu]

If the head was leaking you would think that it wouldn't be holding pressure.

What is the standard operating temp on these? I figured it would be up to around 120C, meaning 100C wasn't over the top I thought.

Should you replace the hose between radiator and the overflow bottle in case that is acting up preventing the coolant flowing back in to radiator on cooling?

[nj swb]

Reasonable assumption, but I've heard stories that sometimes the leak (e.g. a crack) only opens at higher temperatures, and will close again as the engine cools. Real or myth I don't know.

But this is a good question. On releasing the radiator cap, if escaping air is heard, is it over-pressure venting out, or vacuum sucking in? Is the radiator cap somehow not letting the overflow return?

Are the radiator hoses tight when its cold (before releasing the cap) or soft / spongy?

[pharb]

Have twice had the water pump mounting O ring leak when at operating temperature, but not when cold.

Both times took quite some time to find as the coolant would also evaporate as soon as it leaked out when at operating temp.

However this is unrelated to pressurising or overheating.

[jrmc47]

Reasonable assumption, but I've heard stories that sometimes the leak (e.g. a crack) only opens at higher temperatures, and will close again as the engine cools. Real or myth I don't know.



But this is a good question. On releasing the radiator cap, if escaping air is heard, is it over-pressure venting out, or vacuum sucking in? Is the radiator cap somehow not letting the overflow return?



Are the radiator hoses tight when its cold (before releasing the cap) or soft / spongy?

The hoses are tight when cold spits a little coolant out when cap is opened.. Am going to pull the motor and auto trans to convert to manual soon so I will rip the head off and have a look while engine is out.. I have a spare head on my other motor so I might just swap it over and send mine off for crack testing, although I am not hopeful of a good outcome

Sent from my LYA-L09 using Tapatalk

[disco stu]

Can you pressure test cooling system while it's hot to check it's leaking pressure before going ahead and ripping the head off? Just thinking of some way for you to check if it's needed before committing to the work/expense you are intending

Combined with the test erad mentioned for exhaust gases in cooling system water, might save you some time and money

[erad]

I once had a Range Rover which used to leak a had gasket only when hot. On a long uphill section, I could feel the power drop when the temperature gauge reached a certain point. I had to guess which head was blown, so I opted for the one which was hardest to remove. Once it was off, I could a trace where the casket had (hopefully) blown. I had the head shaved slightly and put a new gasket on. No more overheating problems after that. All cylinder compression testing showed no leaks because by the time the spark plugs were removes, it had cooled down sufficiently for the gasket to seal again.

Aluminium heads on cast iron blocks are a potential source of problems, although in this case the Rangie had an aluminium block (with cast iron liners pressed into place).. Even so, this would have caused the problem because Aluminium expands at a faster rate than Cast Iron.

[jrmc47]

Can you pressure test cooling system while it's hot to check it's leaking pressure before going ahead and ripping the head off? Just thinking of some way for you to check if it's needed before committing to the work/expense you are intending

Combined with the test erad mentioned for exhaust gases in cooling system water, might save you some time and money

Yeah stu.... It holds pressure when cold and builds pressure when hot.. Went and picked up a mates caravan today and it hated it... 120 c most of the way home... Just trying to show its weakness and where the weakness is..