Hi All , Some of you may have seen my thread from a couple of months back entitled "300tdi Coolant Gushing " , out of the expansion tank that is , with overheating and no circulation or warm air . I never managed to resolve the problem , but decided to finish the restoration and come back to this later , which I am now doing . I hope someone can point me in the right direction , because I'm stumped . Starting from cold , the temperature will start to rise within a couple of minutes driving , and a minute later will head for three quarters on the gauge . The coolant rises in the expansion tank , without bubbling , if i drove it for any longer than a few minutes it would push out under the cap . bottom hose and radiator remain cold . System was filled correctly , radiator , thermostat , hoses , water pump , and tank cap are new . Heater is not blocked . I tried the " coke bottle " trick in the expansion tank but the coolant just kept on rising , there were no bubbles in it though , I tried the same thing in the thermostat housing and it bubbled ferociously , as the temperature rose the bubbling eased off and the coolant slowly rose up and filled the bottle . It still overheated . I removed the thermostat , it overheated just as quickly and to the same level , although the radiator and all hoses now got warm . Heater still blew cold . I also carried out a sniff test in the expansion tank , also in the thermostat housing and radiator after the coolant had done it's usual trick of migrating to the tank . No indication of combustion gas in the coolant . Now for the bizarre bit .This problem was apparent on my first start up after renewing the cooling system , in fact it was there when I acquired the project . On my second start everything worked perfectly , temperature stable , coolant circulating , heater blowing hot air . On every start since then , the problem has been there . Thanks for any help .

This is gonna sound daft, but I suggest you make sure that the coolant is actually getting hot - forget the LR gauge use something better - a thermometer of some sort... non contact laser are cheap enough these days...

my first suggestion would have been to remove the thermostat, since this may have blocked the flow, either by being faulty or by being in back to front. But you have tried that, and it makes no difference... =

Ok, so the next thing is to check you actually have water flowing, cos, without the thermostat, the engine should take an age to warm up..... - i would suggest re-bleeding the system to see if you can get the heater working. It sounds like the water pump is duff to me - but i haven't seen a duff new water pump for years ( drive pin was missing from the impeller - IIRC on a triumph herald )

If you have water flowing, and the rest of the system is new, then I suggest your bubbles are pressurisation, but its late, and my tramadol is working, so YMMV

Thanks for reply , the engine gets hot to the touch so I assume the coolant inside it is also hot ! I'm pretty sure it doesn't circulate for long . If I start the engine with the thermostat housing or rad bung off , then the coolant splurges out all over the place , so I reckon that's it being pumped . It doesn't take too long to migrate to the expansion tank , leaving the rad down about 3 inches and the thermostat housing empty . I suspect at that stage no coolant is being pumped , only pressurized . I've drained and refilled the coolant several times by different methods but the result is always the same .

I'd remove the heater core hoses, tape or hold a standard garden hosepipe to one of them, and turn the tap on steadily, see if water flows through the heater core. If it does, work the other way and establish a flow around the rest of the system, you might need to take the thermostat out. Then do the same as best you can on the radiator. There's a baffle system inside that can fail and block itself.

Don't forget a 300Tdi radiator also has an oil cooler, check your oil is at normal and can also flow through the rad.

Basically isolate the heater, check it, isolate the radiator, check it for volume and flow, and similarly all hoses ...

When I used to fill my system I just poured in at the tank, with the top off the rad, and off the thermostat so air could be released. Start engine, on tickover, keep filling and squeezing water hoses top and bottom rad etc. Tighten Thermostat top first then rad, whilst they're over flowing.

Can you beg or borrow a proper thermometer? engine will be hot to the touch in no time - most of the fuel it burns gets converted to heat....

Paul D said:

..... There's a baffle system inside that can fail and block itself.

Click to expand...

Unless the HG has gone big style, this is the sort of problem you must have...

Could be a cracked head or porous block, also the rad ought to have a back flush

I've already put a hose to the heater pipes and it flowed freely and clean . Does it matter which hose goes to which port on the heater ? I've tried it both ways but it made no difference . Looks like my next move is to drain my new coolant into a clean container ( third time now ) and get the hose out . Can't imagine the newly re cored radiator is blocked , it heated up all over when I had the thermostat out . The engine block could be a different story . Before I drove the thing the few miles home I had to replace two missing core plugs from the block and one from the head . Whether it was ever driven like that I have no idea , all I know is it started right up with some diesel and a new battery and drove home with great power and no smoke . Not bad for an engine that had sat in a yard for six years !

Put the garden hose to it yesterday , water flowed freely in every direction , made no difference . Local mechanics are puzzled , I've a few more lined up to come along and scratch their heads ..

Consensus of opinion among local mechanics is head gasket or cracked head .

dogdog1 said:

Consensus of opinion among local mechanics is head gasket or cracked head .

Click to expand...

either way head needs to come off which is an easy job ,put some pics up before you clean head or block,and undo block drain prior to undoing head bolts

Will do .

Well , I finally bit the bullet and took the head off . The gasket was clearly burned between 2 and 3 , carbon in the same area on the block and head , Two of those little triangular things in the head were very corroded , and there is pitting towards the sides within the " big circles " of 2 and 3 ( what do you actually call those ? ) although there is no sign of warpage or cracks . Time for a new head would you think ? One other thing , the current gasket is a no holer . I bought one of those Toolzone magnetic base dial gauges but I'm wondering if they are accurate or should I just go for another no hole gasket ?

measure pistons protrusion and get the correct gasket , a thicker gasket was probably fitted to account for previous head skims, skimming head brings valves nearer pistons just as the amount piston protudes does

Measured protrusion with dial indicator today and highest reading is 65 on the dial . So that'll be a two hole gasket . To ensure pistons were absolutely level with the deck I raised them until they just made contact with a straight edge and the 0.05 part of a feeler gauge would not go across either the pistons or deck . I then placed the indicator on the fore and aft of each piston just in from the edge , zeroed it in and took the reading . many times over and resetting the pistons to level before taking each reading . Just to double check the readings were as accurate as possible I placed the 70 part of a feeler gauge on the deck and and ran my straight edge towards it across the piston top and the straight edge stopped against it , but slid across the 65 feeler . Which makes me think you could do this job just as well just with a feeler gauge and a straight edge !