Early Cooling System - Help Please

[timscarth]

Hi all

I'm having issues with the temperature guage reading at 90% when it read 50% up to last weekend. I just don't understand what's going on and I'd really appreciate some help. Read below for the background and what I've done so far.

What I have
I have a 1983 T25 with 1.9DG engine, factory PAS and auto gearbox. The cooling system is an early cooling system with 32mm pipes front to back and metal thermostat housing.

Background
I had an overheating issue last summer when driving over some steep hills in Wales. I fitted a chicken switch while at a campsite and it got home, temp guage sitting at around 50%.

What I've done so far
I decided to cut my losses and replace everything I could as the front to back coolant pipes looked horrible.

I've therefore done the following

• Metal coolant pipes - replaced with front to back stainless steel
  
• Heater matrix pipes - replaced with new straight hose front to back
  
• Engine bay large pipes - replaced with silicone pipes from Brickwerks
  
• H shaped junction box by water tank - replaced
  
• Dalek cap - replaced
  
• Water pump - replaced
  
• Alternator - replaced
  
• Junction at the back of engine bay with breather - replaced with specific oem part with extra out/in to auto gearbox
  
• Metal pipe from bottom of water pump - replaced
  
• Coolant - new G11 (old coolant was horrible orange colour)
  
• All jubilee clips - replaced
  
• Heater control cable - replaced
  
• Thermostat - replaced
  
• Radiator thermo switch - replaced
  
• Various gaskets - replaced
  
• All other rubber coolant hoses in engine bay - replaced with parts from Brickwerks.
  
• I also replaced all fuel lines, clips and fuel filter.
  

What's happened

• I live in Birmingham and I did the work at a workshop in mid Wales.
  
• Just before I set off, the fan motor stopped working and the fuse popped. I've ordered a new fan and resistor which has arrived and not been fitted yet. I can therefore only check warm through vents when I'm moving.
  
• I drove the bus back two weeks ago and it got home with no problems, approx 80 miles cross country and a bit of motorway. Temp guage at 50% all the way home and vents warm when I wanted them to be.
  
• Wen I checked the following morning I noticed that one of the hoses was weeping a bit. I tightened the jubilee clip and put approx 500ml of water in the pressure tank.
  
• I took it for a test drive on Thursday and it seemed to overheat on the guage. Temp guage rose as usual but didn't stop rising until it went to top and red light started flashing. I stopped the bus, let it cool down and drove it home (repeating twice as temp got high so I didn't break anything).
  

What I've done now

• I checked and I'd lost quite a bit of coolant.
  
• I've tightened all jubilee clips
  
• Followed the topping up and bleeding instructions on brickyard (2000rpm, fill up, bleed from rad, etc, etc.)
  
• I don't believe there's any air in the pipes as I can't get any more out when bleeding and when engine cools down I've not lost any water.
  

What I'm now seeing

• Starts fine and warms up but temp gauge climbs to much higher than it did before.
  
• Thermostat opens but only after it's been sitting at 85/90% on the guage for a few mins.
  
• Heater matrix pipes both get warm
  
• Once thermostat opens, both coolant pipes get warm and rad is warm all the way up
  
• Fan hasn't started automatically although I have checked it with a paperclip and it works fine and it does bring the temp down to about 70% when fan at maximum and doing 2000rpm.
  
• I've measured the resistance of the temp sender. At 90% on the guage it's at about 100ohms.
  
• I've replaced the clip which connects to the temp sender as the cable as a bit frayed.
  

I'm stuck. Does anyone have any ideas what could be happening? Why is it different now compared to when I filled it up after replacing everything? What else should I check? Could there be an airlock causing a high reading or is something else going on? One thing I could buy is an infrared thermometer so I can see what the coolant temp actually is.

[tandemsandy]

Mmmmmm....
same early 1.9 DG here, only manual.
The new thermostat operating correctly and the new rad fan not closing makes me think the actual water temp is fine, and the gauge is reading high.  
Had an issue in my beloved Mazda 323F where the temp gauge would randomly climb high, which prompted me to whack on the heater and open the window, which dropped the temp.  After months of this I then realised the temp gauge dropping was related to the electric window operating, not the heater dropping the temp.  After more months found a knackered earth cable from the engine block - fixed that and the problem went away!!
Could be a simple electrical gremlin somewhere. But then it is a T25............

Rob

[Mocki]

First thing I would say is get a infrared thermometer and check what the temperature actually is . The wiring is 40 years old and if it’s corroding or gone tanished and black internally the resistance has changed , it could be adding to your 100ohm temp sender and increasing the reading the gauge is giving and you may not be over heating at all ?

Also , the darlek cap could be faulty even if it is new and allowing less pressure so the temp can go higher ( being under pressure stops coolant boiling at 100°c )

Also the single pin temp senders are known to give different readings when you take one from a old thermostat housing and put In a new one due to brass / aluminium/ corroded threads alto green the resistance to ground

[toolsntat]

I admit I know absolutely nowt to help you with your problem but I must commend you on what's probably the most informed question for help I've seen.
Cheers Andy

[timscarth]

Tnanks all for your help & suggestions so far.

So I took it for a drive yesterday. made it 70 miles with temp guage solid (at 80%) then it started flashing red and guage went off the scale. It seems a pipe or two may be still weeping and losing coolant when hot, then sucking in air as it cools down.

Decided to not take any risks and got RAC to recover me back home.

Plan now
1. Order a new coolant temp sensor and check it, plugged into the van, at a known temperature to see what the guage displays. By my reckoing, at 87 degrees C it should be half way which is when the thermostat is meant to open.
2. Order a new coolant level sensor and again check it for resistance in known water depth. Again, plug it in to the van and see what happens.
3. Check all hoses (again). I believe a couple of bits of straight hose I've used are too hard and not nipping up tight enough. I'll order replacements.
4. As I mentioned in the first question, the heater motor needs reoplacing. Might as well do that now before re-bleeding the system.
5. I'm going to buy a thing to check the coolant mix as with all the top ups, etc I've lost track of the mixture and I want it to be right.
6. I'm going to buy a new radiator bleed screw and washer. as it doesn't seem to be very smooth as I open it.
7. I've ordered an infrared thermometer

Questions
1. Do you think it'd be worth exploring whether I have leading head gasket or split heads? How would I go about checking this?
2. The hose from the bleeder junction going to the centre os the engine bay seems to still be leaking a bit. This was originally braided hose but I replaced with rubber (as above I think a bit too hard). Does anyone know where I can get replacement braided hose of the correct spec?
3. Anything else anyone can think of?

[timscarth]

I admit I know absolutely nowt to help you with your problem but I must commend you on what's probably the most informed question for help I've seen.
Cheers Andy

Thanks very much. Our bus is a Holdsworth too, blue pop top.

[Aidan]

is it blowing coolant into the top up tank behind the flap when it is hot ? If it is then it could be a head seal issue or more likely a poor darlek cap
Any decent garage would have the test gear to check the darlek cap, the pressurisation of the system and do a sniff test for products of combustion in the coolant
Birmingham is a big place but there must be a decent T3 friendly old school garage there somewhere

[timscarth]

is it blowing coolant into the top up tank behind the flap when it is hot ? If it is then it could be a head seal issue or more likely a poor darlek cap
Any decent garage would have the test gear to check the darlek cap, the pressurisation of the system and do a sniff test for products of combustion in the coolant
Birmingham is a big place but there must be a decent T3 friendly old school garage there somewhere

Hi Aidan

No, the level in the top up reservior behind the number plate isn't changing at all.

I have a pump which can pressurise the system to 15 psi and the dalek cap holds (although I have ordered another one anyway with all the other stuff that's on the way.

[Aidan]

Sounds like a wiring issue causing gauge to misread then

[timscarth]

Sounds like a wiring issue causing gauge to misread then

So, my plan to either confirm or rule that out is as follows;

I've ordered a new temp sensor and level sensor. I can then test thwem with known levels and temperatures against the existing sensors and measure ther resistance I get from them. I can also plug them into the bus and see what the gauge reads with certain known inputs (for example 87 degrees should be about middle on the temp gauge as thats when the thermostat should open.

[tandemsandy]

Without looking at Vinnie I can't remember what the options are for attaching it, but running an extra earth cable from as close to the temp sensor housing back to nice shiny metal bodywork won't do any harm.
When diagnosing this on the 323F I also ran a temporary wire that completely replaced the wiring between temp sensor & gauge - 30+ year old wiring can increase in resistance.  You could crimp a spade terminal onto a long length of wire, run it from the temp sensor out through the engine hatch and thru the inside of the van and graft it into the wiring behind the dash - eliminating the old wiring means the gauge will see the same resistance as the sensor - it might suddenly behave correctly!