Thread: 300 Tdi Overheating with a difference ?

Originally Posted by vnx205

My own experience with a thermostat that was stuck open was that it increased the fuel consumption....................................... .

With a modern ECU controlled engine the engine temp is used to vary the mixture, ie. run a bit richer when cold and warming up, just like an old manual choke and lean off when up to temp. If the thermostat is crook and the engines running cold then it's like the chokes pulled out and uses more fuel.


Deano

Originally Posted by PAT303

None of this adds up, ........................................ Pat

I had the engine running for about 5 minutes with no apparent problems before I drove it, sorry I didn't mention that earlier, I just took it for granted.

On delving a bit deeper I've found a number of cooling associated issues here, some minor, some major.

1/. The head gasket is probably leaking (slightly) to the water jacket on combustion.

2/. No thermostat.

3/. Pressure cap not pressurising.

4/. No inhibitor/glycol in the coolant.

5/. Viscous coupling siezed.

6/. Crook (original) P gasket, probably the root cause of the whole exercise.

and I haven't even looked at the 'new' radiator yet, it might be as good as the 'new' thermostat.

I reckon a mixture of poor coolant circulation through the engine due to no thermostat coupled with coolant (water) being heated up/forced out by combustion pressure and a 100 degrees boiling point coolant as opposed to 120+ degrees with pressurised glycol mix coolant all contributes to the water in the head boiling and creating steam/pressure. Water isn't being sucked back into the combustion chamber because the gasket 'blow' is minor and the lack of pressurisation of the coolant means coolant isn't forced back into the combustion chamber(s) when the engine cools.

For todays exercise I'll check the radiator and check that the fan blades are 'pointing in the right direction'. Be funny if it had the wrong fan and it was blowing backwards.

I'm pretty confident fixing these issues will solve the overheating problem. The (new) head seems to be in good condition as does the bore which still has honing marks evident.

Deano

So no real issue's then . Pat

300TDI amateur detectives course

Originally Posted by THE BOOGER

300TDI amateur detectives course

Where do I enrol??

Sent from my HTC One XL using AULRO mobile app

A few years ago, our local mechanic inadvertently fitted the wrong t/stat to my 300 tdi. It had been labelled as suitable for that engine, but was not as deep, so the back seal didn't touch the housing. The head gasket blew very quickly. At the time, I read on an english forum, that the rear seal on the t/stat holds the coolant in the back of the engine, and if the engine is run without the t/stat, the back of the engine would run out of fluid and cook, blowing the head gasket. I don't know if this is actually true, but it fitted what happened to my engine.
Don

Sounds pretty right to me Don. This is exactly the information I'm after. I reckon mine suffered from the same problem as yours but in my case no thermostat all. Either way totally stuffs up coolant flow in the engine, especially in the head leading to head gasket/head failure at best.

On mine I reckon the original problem was due to P gasket failure which resulted in head gasket and head failure.

The head, head gasket and water pump have been replaced but the P gasket wasn't and it was rotten. Didn't even have any sealant put on it when the head etc was replaced. I reckon this has caused coolant to continue to leak from the system resulting in the new head gasket also failing. At this stage someone has removed the thermostat thinking it will help but in fact just made the situation worse. Fortunately the new head seems OK.

The seized viscous coupling is, I think, just a side issue (and it does have the right fan attached). The pressure cap has probably failed due to over pressure.

The radiator (cheap Chinese replacement) seems OK but impossible to test its flow rate with its inbuilt bypass hole (IMO a terrible design) and is way too cheap/weak to pull a tank off to check and rod, so I'll just have to 'suck it and see'.

To add to the original list of cooling system issues someone had cleaned the radiator at some stage with a pressure cleaner and severely flattened about 20% of the cooling fins. A couple of hours work with a pair of duck bill pliers and a small bladed screwdriver have fixed this problem.

Not much left to stuff up in the cooling system really, I reckon I've got the lot.


Deano

All fixed now, all good .

To add to the general tale of woe is no radiator/fan shroud which is quite important for good air flow; and to be a bit pedantic there was no 'filler' strip between the radiator and the intercooler which leaves a 1cm or so gap for air to bypass the radiator/intercooler.
Also temp. gauge sender unit 'reading high', replaced.

While these issues might seem a bit petty it all adds up. The 300 Tdi has a good cooling system but not a lot of overhead for 'mistakes'. So to recap...

1/. Head gasket leaking (slightly) to the water jacket on combustion.

2/. No thermostat (removed thermostat was non bypass type and was found with replaced [nothing wrong with it] water pump in back of vehicle.

3/. Pressure cap not pressurising.

4/. No inhibitor/glycol in the coolant.

5/. Viscous coupling seized.

6/. Crook (original) P gasket, probably the root cause of the whole exercise.

7/. No radiator / fan shroud.

8/. No radiator / intercooler filler strip.

9/. Temp gauge sender unit faulty (reading high), misleading.

I really can't think of anything else that could possibly go wrong / be made to go wrong in the 300 Tdi cooling system.

This ongoing cooling system failure was basically caused by a poor initial diagnosis (failure to identify leaking P gasket) and was compounded by a poor repair (new head, water pump and wrong thermostat), and even further compounded by incompetence (removing the thermostat altogether, not to mention 'throwing away' the radiator / fan shroud) and still not noting the leaking P gasket. It's nothing short of a miracle that the new head was not also ruined, perhaps the (failed) high reading temperature sender helped here .

Any way it's all fixed now, but the whole mess was so avoidable with just a little bit of knowledge / expertise.

So if you're lucky enough to have a Landy with a 'real' non plastic / electronicky 300 Tdi diesel, PLEASE..................... check your P gasket for leaks.



This picture shows the typical 'rust streak' from a leaking P gasket on the LHS front side of a 300 Tdi engine.

If yours looks like this then it's a hell of a lot easier and **** loads cheaper to replace the $12 P gasket than the whole head/head gasket/bolts etc when the engine cooks itself.

'Dave' (all Hail Inc.) sells a very good 'get out of jail free', coolant level alarm kit to let you know before meltdown if your coolant level is low and is IMO a very good investment.

https://www.davesitshop.com/emporium...&product_id=48

Preaching over.................

Thanks

Deano