Thread: TDI 300 Overheating problems

Originally Posted by Spel1

Don't know for sure that is your problem, it just sounds like the symptoms I had with my radiator. I would call Natrad and ask how they cleaned it, whether it was a just a chemical flush or was rodded, (which involves taking it apart and physically cheaning the tubes). Wouldn't hurt to ask and would help with eliminating possibilities. Simon

I think I'll take it to someone else to get done. I wasn't happy with Natrad anyway. Natrad said they pressure tested the radiator to 25PSI but when I got it home it lost all of the coolant as fast as I was pouring it in. They failed to see the 5mm slip in the side. They fixed it with no complaint but it doesn't instill confidence.
Regards
Jonesy1972

Thanks for the post Jonesy1972. I'm experiencing the same problem at the moment. Engine monitor sounds like a wise investment. Keep us posted on the outcome.
Nundle

Originally Posted by Nundle

Thanks for the post Jonesy1972. I'm experiencing the same problem at the moment. Engine monitor sounds like a wise investment. Keep us posted on the outcome.
Nundle

I am currently enquiring about an aftermarket radiator from the UK for $152 excluding freight. I'll let you know the freight costs and how many core it is when they get back to me.

Regards
jonesy

How many core is a TDI 300 radiator? I thought they were a 4 core but I can't check without dumping my coolant.
I received an email from Rimmer Bros last night to say their radiators were "2 core, I think". I asked for them to find out definately but they returned by asking how many core was mine.
I know the series 3, 2.25Lt petro was a 3 core and I can't see them going less.
Any ideas/help?

regards
Jonesy

The efficiency of the radiator will be degraded even if you just rod it. The galleries will never be the same as new. A degraded radiator will not cut it on hot humid days – humid days mean less air density and less heat transfer from radiator to the air. The temperature differential between inlet and outlet will always be greater in the new radiator. Coolant flow rate through the rad is critical to the rate of heat exchange to the air. Under heavy load a 2.5Tdi needs more than 170 litres per minute passing through the system – E.G the minimum safe flow figure for a 2.5TDi jeep at 88km/hr on a 6% climb 35degrees and 90% humidity is 195litres/min. The coolant mix at the rad inlet was measured at 104 degrees and the coolant mixture was 18% vapour under this load.
At the 200,000 km mark just budget for a new radiator and a complete cooling system renewal. Do it all at the same time as you do the timing belt – new pump, thermostat radiator, viscous fan, expansion cap, hoses etc. Throw the old radiator away as it will never be as efficient at transferring heat to the air as a new one. Use some gauze to stop insects bodies from blocking the rads.
A 2.5litre tubo diesel must dissapate twice the energy to the cooling system as a 2.5petrol - Heat rejection of a 2.5litre turbo diesel is 144kW whereas a 2.5L petrol engine only requires 76kWi.e the radiator and oil cooler must be able to absorb double the energy.
Here is some ifo on how of how much heat needs to be dissappated by this radiator in a 300 TDi.
I have an 97 300 TDi with EGt guage, aftermarket water temp, oil temp,oil pressure, boost guage and an accurate head temp sender attached close to the exhaust port on number one. I also have low coolant alarm plumbed into top of new radiator from enginesaver.com.au
Normal EGT is 300-350 and water 85 – factory guage shows under half .
Under load, EGT elevates instantaneously to 550 degrees celcuis and will stay there. Boost is about 11- 14psi. The head temp immediately rise to 100-105. The water follows quickly from 85 to 95. Oil temp rises rapidly thereafter. The factory guage does not move. All my cooling system components are new.
Switch the AC on, maintain the load, and the water temp moves higher very quickly up to 99.
Any weakness in the system such as a slight pressure release or less than 50/50 coolant mix will cause localised nucleate boiling in your head resulting in more trouble. The resulting vapour travesl to the water pump where they can cause pump cavitation. Any minor cavitation at the pump results in less flow. This leads to further issues.
Nucleate boiling is the same as the bubbles that start forming in the bottom of your jug at home – and yet actual boiling has not happened.
The ethylene glycol water mixture can easily operate as a liquid/ vapour mixture. The vapour content is determined by temp and pressure. Once the coolant temp is reduced below the saturation temp (100c in a 50/50 coolant mixture) then the pump will receive liquid only correct flow rate will result. In a 50-50 mix ethylene glycol water mixture the boiling point is 130C.
Nucleate heat transfer is a hybrid form of convective heat transfer. The coolant is allowed to vapourise against the engine. This absorbs far more energy than by conventional means. The vapour is condensed in the radiator. System px is very important in this method and expansion of coolant vapour must be accommodated with an expansion tank. If the coolant reaching the pumps has any vapour or is too hot then the flow rate drops immediately.

So to avoid nucleate boiling you have to have good quality and correct ratio of coolant – This will allow the coolant to operate under pressure without loaclised/nucleate boiling. That way the pump and radiator can continue to function at their optimum.
It’s a highly tuned system. A slight weakness in one item will overload the others. If you want the engine to go through to 500,000km then you should budget for a complete cooling system overhaul.
BTW – this applies to all vehicles – there are just as many so called bombproof Toyotas and Nissans being cooked every day out there due to only replacing cooling system parts as required.

An excellent article Peter and thank you for the time you spent writing it up.
The only small criticism I have, is that you haven't referenced your sources.
But then who am I to say this.

Originally Posted by peter51

The efficiency of the radiator will be degraded even if you just rod it. ---- Throw the old radiator away as it will never be as efficient at transferring heat to the air as a new one. ---- It’s a highly tuned system. A slight weakness in one item will overload the others. If you want the engine to go through to 500,000km then you should budget for a complete cooling system overhaul.

I have fitted a new radiator to one of my 300TDi D1's ( 'Fred' ), that one action alone cured all the problems that I was having when towing heavy loads.

Any weakness in the system such as a slight pressure release or less than 50/50 coolant mix will cause localised nucleate boiling in your head resulting in more trouble. The resulting vapour travels to the water pump where they can cause pump cavitation. Any minor cavitation at the pump results in less flow. This leads to further issues. --- If the coolant reaching the pumps has any vapour or is too hot then the flow rate drops immediately.

To me, your description of pump cavitation has the reason that the cheap after market water pumps fail so soon.
The plastic cage around the water pumps bearing rollers, isn't up to the extra heat generated under Australian conditions, the bearing rollers cage then deforms with extra heat and lets the water pump shaft move into misalignment .

BTW – this applies to all vehicles – there are just as many so called bombproof Toyotas and Nissans being cooked every day out there due to only replacing cooling system parts as required.

Some cooling systems have been designed with a far greater threshold to guard against temporary overload, most tractor designs have this feature.

Thanks again Peter for your work .
.

Regarding producing references - Here they are.
The figures I quoted were taken from a collection of automotive engineering articles in regard to vehicle cooling systems – from the state library. In that collection was a report on the introduction of the Jeep diesel into the tropical markets. The petrol version never overheated, whereas the 2.5 turbo diesel continually overheated. Recall that I said turbo deisels typicalyl require twice the heat rejection as a petrol of the same capacity.The information below is taken from the engineers report on how they modified the cooling system to stop the overheating. It is a good example of how much design goes into cooling systems and obviously how the owner must keep up with the maintenance.
Attached is a table showing temperatures and flow rates before and after modification. You can see that for a 2.5 turbo diesel quite high flow rates are required. The 300TDi would require similar figures – you can see that all components must be in top condition to maintain the design rad inlet temps, outlet temps, vapour content, coolant flow and static pressure at pump inlet. The total pressure being a combination of dynamic (fluid speed) and static pressure
The table is attached below.
In short the problem was lack of flow rate, excess vapour at the pump inlet and too low static pressure at the pump inlet. The radiator was also enlarged to allow for an increase in flow rate.
Increase in cooling system pressure will increase the boil point. This allows higher engine temperatures and better economy. This increased pressure also reduces the amount of vapour in the system and therefore lowers cylinder head temperatures.
If there is an overheat of the coolant , or drop in pressure, boiling – then vapour will form and as the coolant enters the pump inlet, this vapour will expand due to the low pressure at the centre of the pump. As the amount of vapour increases at the pump inlet then the flow decreases. When the pump reaches a critical vapour volume it will cavitate and coolant will no longer flow A typical centrifugal pump can only handle up to 25% vapour before it begins to reduce coolant flow rate.
If the flow rate is to be increased, as in the above example, then the radiator must also be increased to handle this flow rate.
Additionally, the inlet pipes of the pump must be as large as possible to balance the inlet and outlet conditions.
Increased flow rates were achieved by increasing the diameter of the pump impeller and pulley size was reduced – 1.15 drive ratio to 1.43 ratio. In the Jeep diesel case above the impeller blades were only slightly increased in diameter up to the maximum of the original casting, however more importantly, a cone head pump impeller was moulded into the centre of the impeller to more effectively force any vapour through the pump.

Hopefully all Landrover owners and especially those with old turbo diesels will dig deep into their pockets to completely overhaul their cooling system in order to restore it to design conditions
Regards
Peter

I received the new viscous coupling yesterday and did a run up the hill, air cond on, 3000RPM in 3rd gear doing 80km/h on a 35 degree day and she didn't get hot (normally she would).
When I pulled the old viscous coupling off I was clear to see it had leaked.
The only thing left to replace on the cooling system is the radiator but I need to know how many cores does the TDI300 radiator have?
Regards
Jonesy
PS. If you buy a viscous coupling do yourself a favour and buy the $14 spanner to remove the old fan.