Thread: 300 Tdi Overheating with a difference ?

To boil in that sort of distance I would be checking the block, gasket and cast iron head ? all line up also the water flow thru the block

AM

The second most important part of a 300tdi thermostat is the bypass valve. When the thermostat opens the bypass valve closes the short path back to the water pump inlet. Without the thermostat present the bypass flow is too great for enough cooling flow through the radiator. On an old V6 Volvo I once had the privilege of working on, I had to block the bypass channel with a pipe plug so it could be driven at all. On the 300tdi you could just insert a plug into the short bypass hose adjacent to the thermostat housing. Then it would cool quite adequately, all other things being OK. Even some temporarily applied hose pliers would test the theory.

I will probably get shot down in flames and die a horrible death, but here goes.


My understanding is the thermostat controls the internal temperature and opens to allow cooler coolant in as required. So, it could be that having no thermostat means that the coolant does not slow down enough to cool down at the radiator.


Or, in other cases, remains shut to allow the engine to come to temperature and then remains open for constant flow of coolant at a regulated temperature as designed by the manufacturer. So removing the thermostat should have just meant a slower warm up.


If both these ideas fail, you have to wonder if there is a blockage inside the block, in which case a big flush followed a flow test????????

300tdi and overheating is very common as you know if you can figure it out you wil be everybodies best mate

Originally Posted by tonic

I will probably get shot down in flames and die a horrible death, but here goes.


My understanding is the thermostat controls the internal temperature and opens to allow cooler coolant in as required. So, it could be that having no thermostat means that the coolant does not slow down enough to cool down at the radiator.

I don't think that coolant can ever get up to a speed too high to prevent heat loss through a normal radiator. If the flow speed is higher the coolant drops less in temperature but loses more heat due to the extra flow rate. The whole surface of the radiator is hot, not just the top corner. So the difference in temperature between the coolant inside and the air outside the tubes is higher over a bigger area of the radiator.

The thermostat's real job is to change from flow through the bypass to flow through the radiator in a smooth manner. A good flow rate is essential in keeping the whole engine even temperature wise to reduce the chance of head gasket failure, eg when the head is frequently much hotter than the block. You don't actually want short pulses of cold water added to the block, varying amounts of cold added to a varying amount of hot circulating coolant is the best way to stay around a reasonable operating temperature.

Originally Posted by Ancient Mariner

To boil in that sort of distance I would be checking the block, gasket and cast iron head ? all line up also the water flow thru the block

AM

Is someone making cast iron heads for Tdi?

Originally Posted by d2dave

Is someone making cast iron heads for Tdi?

The OP said steel hence the ? The only steel heads I know of are from steel fabricated engines I don't know of CI for 300tdi

You gentlemen are quite correct of course, I do not have a Tdi 300 with a unique steel head, it is of course alloy. What I was trying to explain was that the density/grain of this LR (replacement) head is much denser than what is 'normal' with the original Tdi heads I have worked with and of a consistency comparable with good cast steel.

This is from an original head and the poor quality of the casting can be easily seen.



and while this isn't the same as above hopefully the better quality casting is evident.



I may have been a bit premature with my discounting of the head gasket being crook. Here's a detail shot of the water gallery 'hole' between cylinders 2 and 3 from both sides of the gasket.





Whilst there's no sign of coolant in the sump, combustion chambers or inlet/exhaust ports or oil in the cooling system I reckon exhaust gasses may have been able to squeeze past here.

My original point about the missing thermostat is that coolant would be able to bypass the radiator and return directly to the engine until it overheated.

Tonic, no flaming demise here. You're pretty spot on with your assessment for a 'non bypass' thermostat. With a bypass thermostat there's an extra bit on the end which has the thermostat acting as a two way valve. ie. allowing coolant to go either to the radiator or back to the engine to allow more efficient warm up. When it's missing there's nothing to regulate which way this coolant goes.

Bypass thermostat on the left, non bypass on the right.



What I'm asking is, has anyone out there run a Tdi 300 without a thermostat and what was the result ?

Deano.