Bedford TK

[Dcal]

There should be a one way valve built into the radiator cap.
As the system cools the water contracts and causes a partial vacuum so without that valve, or if its faulty, the hoses will collapse.
Try and new radiator cap and check that it is the correct pressure rating.

Do you lose a pint of water every day or do you lose a pint of water and top it up and then lose the same pint the next day (if you know what I mean)
If the pressure rating of the cap is too low, or if the cap is faulty, you could easily lose a pint of water.
The caps and the cooling system are easily checked if you have access to the kit, any decent garage should have it.
Cap are (or used to be) cheap so people just changed them but testing it will confirm or eliminate it as a problem.
I'm not sure (it's been 30 years since I worked at a TK) but I think the cap should be 15psi. If it is not making the pressure you will you lose water (if the pressure can't increase the water will just go out the overflow)

Are you sure the heater needs bled? If it is working it should be OK.
I don't remember them being tricky to bleed. It might be symptomatic of another problem.
Does turning the heater on full when you starting to overheat reduce the engine temperature?
If you have a problem with air in the system the heater will be the first thing to show you have a problem.

e

 

[mylesdw]

Interestingly the heater works very well and yes, it can be used to reduce the engine temperature. I wondered about it because I cannot see any way that air could ever get out of the heater. Both pipes come up from below and there is no air bleed. I filled the whole system from dry and I did not bleed anything. Maybe there is enough flow just to push any air out?

I believe it loses about 1 pint per day; you top it up and it's gone again the next day. No obvious leaks and nothing to suggest head gasket problems.

I'll try a new radiator cap to start with.

 

[Dcal]

If the heater is working well it doesn't need bled, the water pump is able to push the water through the heater matrix and so there is no need for a vent valve.
If it just needs topping up with a pint I'm not sure you have much of an issue.
If you leave it more than a day and it needs two pints after two days and a gallon after a week you certainly have a problem and it should be an obvious leak.

Is there an expansion tank on it?
I'm well past the limit of my memory, but I seem to recall there was one under the DS flap.
The min / max levels on the tank and so volume, is calculated so that the water between hot and cold stays between these marks.
If the pressure in the system is too low (because the cap is faulty or the wrong rating) or the temperature runs too high, the volume required for the expansion of the coolent will be larger and the "extra" volume of coolant will be pushed out the overflow pipe and you will not notice it.
If there isn't an expansion tank you will still need an expansion volume within the radiator.

If it boils all bets are off.

When it's hot or better still overheating and with the engine switched off are all parts of the system and radiator hot? Are the hoses firm I.e. Under pressure? A cheap infrared thermometer is great for checking.
Could the water pump be faulty and not circulating fully?
These old engines can almost cool by convection if it's not too hot. The fact that your heater is working well would make me think this isn't a problem.

Only other thing I can think of and I know you have already checked, but are you sure the radiator and fan are the correct size and the fan is blowing the right way?
Could be that your radiator and air cooling flows are at the limit of the design.
I'm sure export models would have had a bigger radiator and fan.
Could you have a model specified for cooler climes?

 

[DAPPH]

Check the expansion tanks pressure cap .....sound like it's leaking on the rubber seal or there might be a tiny crack in the plastic at the neck .

If it recall thing rightly there is an over flow tube on the expansion tank .. if so put the tube in some soapy water and watch for bubbles.

I've driven various bog standard military RL's & Mk's in Cyprus in 1975 when in June the air temp was over 43 oC in Nicosia . None over heated to my knowledge & they all had thermostats fitted & contained antifreeze for in the winters on top of Mt Troodos it could drop to minus 10 oC or so.


Now for a few confirmation check , can you do a compression test ………. wet & dry to prove that things are OK . Have you pumped up the cooling system when it is cold so it is two or three pounds above the pressure cap rating it should hold for at least a minute

Can't remember if you had the cyl head off if you did .. Did you renew the little connection hose between the head and the main block at the front of the cyl head ?

I've found a few lads who damaged the hose when putting the head on or they didn't quite get the hose clips tight enough .
Changing the connecting hose in situ is possible but it's an absolute bitch, found it was always quicker & more effective to drain the coolant and lift the head up & sit it on a section of broom stick whilst the hose was removed and a new one put on... the head end The hose was greased internally with silicon or Vaseline to get it over the bottom spigot, tape the free pipe clip in place so it stays on whilst your lowering the head down .

 

[mylesdw]

I think the TK does have a bit of a problem with airflow. I have seen at least two here where makeshift air scoops have been added. Driving it this weekend the cooling was fine with the temperature outside less than 20°C, in fact the electric fan never runs in these conditions so I may have to wait for next summer to continue this investigation. In the mean time I think I will replace the cap and possibly rig up a catch-can so that I can see what is being pushed out of the overflow.

Yes, there is a tank under the n/s flap.




The original thermostat had been 'gutted'

 

[mylesdw]

I've driven various bog standard military RL's & Mk's in Cyprus in 1975 when in June the air temp was over 43 oC in Nicosia . None over heated to my knowledge & they all had thermostats fitted & contained antifreeze for in the winters on top of Mt Troodos it could drop to minus 10 oC or so.

Maybe the MKs and RLs had better cooling? The RL looks like it has way better air flow. MK looks the same but I wonder if it had a bigger rad.

I'll try the bubbly pipe trick.

 

[jsf55]

Butting in a bit late on this problem, but I do have some experience ! is this a simple rad set up with only radiator with top and bottom tanks ? does it have a take off on the radiator cap neck ? My thinking is your over filling it ? it needs room for the water to expand when hot, then when you check it the following day it's low. then the cycle starts again, to alleviate the problem run a small bore hose down the side of the rad to a "catch can " I've seen anything from a coke can to a aluminium water bottle and some other exotic stainless stuff used, at least if the water is ejected you will see where it is. On cooling if you have the overflow pipe at the base of the catch can when the vacuum valve will suck water back into the rad.
EDIT ... just saw your reply, you need a hole in the top of the thermostat to allow air to pass through, something about 4mm

 

[8ob]

I have never seen electric fans fitted on big diesels, if they are of adequate size the alternator would probably struggle to keep up. If it was my truck the big mechanical fan would be going back on there.

Bob

 

[DAPPH]

Butting in a bit late on this problem, but I do have some experience ! is this a simple rad set up with only radiator with top and bottom tanks ? does it have a take off on the radiator cap neck ? My thinking is your over filling it ? it needs room for the water to expand when hot, then when you check it the following day it's low. then the cycle starts again, to alleviate the problem run a small bore hose down the side of the rad to a "catch can " I've seen anything from a coke can to a aluminium water bottle and some other exotic stainless stuff used, at least if the water is ejected you will see where it is. On cooling if you have the overflow pipe at the base of the catch can when the vacuum valve will suck water back into the rad.
EDIT ... just saw your reply, you need a hole in the top of the thermostat to allow air to pass through, something about 4mm

In the thermostat housing there will normally be jiggle pin in a hole to allow air to escape past the thermostat when it is in the closed position .

 

[DAPPH]

Seeing the picture of the gutted thermostat makes me think the heating problem was there before you got the truck or it is meant to be like that .

I know you had the rad cleaned. Did you put 4 oz of citric acid in the coolant and run it for half an hour to dissolve it then leave it over night to get it working on any iron residues in the system ? . Then run again in the morning for a few minutes to get all the crud circulating then drain the block & the rad asap

 

[mylesdw]

I have never seen electric fans fitted on big diesels, if they are of adequate size the alternator would probably struggle to keep up. If it was my truck the big mechanical fan would be going back on there.

Bob

Chap I knew ran electric fans all the time on Scammell tippers without problems - reckoned it saved fuel and quieter in the cab but I do wonder. Trouble is the original fan and shroud are gone so I would have to replace it all.

 

[mylesdw]

I know you had the rad cleaned. Did you put 4 oz of citric acid in the coolant and run it for half an hour to dissolve it then leave it over night to get it working on any iron residues in the system ? . Then run again in the morning for a few minutes to get all the crud circulating then drain the block & the rad asap

I'll give that a go next time I drain it down.

 

[colnerov]

Hi, Having no thermostat, or the gutted one, slows the warm up down. It also doesn't slow the flow of water round the system so the water doesn't stay in the rad long enough to loose sufficient heat and you end up with the whole lot too hot.

I think it's going to be a little bit of everything said.

Colin

 

[mylesdw]

Nothing of great interest but fitting a 4kW diesel heater. Having no insulation whatsoever it gets a bit chilly in there in the evenings.



It's Chinese knock-off a German heater and about one third of the cost. I haven't run it yet but first impressions are good.

Sitting it behind the cab keeps it dry and it is nice and close to the diesel lines.



Temperature is controlled by an electronic controller and this little dosing pump and on the far right you can see the non-return valve that I fitted so that a fault in the heater can't stop the truck from running.

 

[mylesdw]

There should be a one way valve built into the radiator cap.
As the system cools the water contracts and causes a partial vacuum so without that valve, or if its faulty, the hoses will collapse.
Try and new radiator cap and check that it is the correct pressure rating.

I bought a new cap and sure enough, it had a spring-loaded air valve that was completely absent from the existing one, so that should solve the hose collapsing problem.

 

[Dcal]

Hopefully that should sort it.
I think there are 2 caps one with the valve that went on the expansion tank and another blank one that went on the radiator. (Like 80s jap cars.)
Someone must have put the wrong one on it at some time in it life.

Also thanks for the tag that my guess might have worked.
Nice touch that.

 

[mylesdw]

I like to try and 'close the loop' with things like that, so that the thread actually has some useful content.

Also important to respond promptly :-)

Went out for a drive the other day, Helen (my better half) drove and found it very easy to drive which was one of my aims - to make it drive more like a modern truck.

The combination of air brakes, power steering, air clutch and the amazing 'bungy on the gear linkage' modification make it all quite civilised.

 

[yoeddynz]

Tin Bashing

I went to our local second hand shop and bought some tools....

I saw that and instantly thought of this...

 

[mylesdw]

I thought I'd update the whole overheating saga.

Having suffered marginal cooling for a few years I was intending to take the radiator out this winter and get it recored with something newer and more efficient. Fate took a hand a month or so ago when the water pump failed on a trip north and the truck ended up at a workshop about 2 hours up the road.

Needed a new water pump so it was silly not to do the rad at the same time. Ian, the workshop owner reckoned the electric fan I fitted was never going to be enough (I think others on this forum voiced their doubts to) so he refitted an original fan and it now seems all good. I've just driven it home 2 hours and some quite mountainous sections without the gauge rising above 90.

It seems that some vehicles, such as bulldozers and Bedford TKs, never generate enough airflow through forward motion and have to rely on powerful engine-driven fans at all times. When I fitted it, I never thought for a moment that it was not a good idea. We live and learn.

 

[p0689109]

Nice to hear from you again. I hope your wallet has recovered from the shock!