Thread: How to compression test a 300tdi

The easiest way is start it,if everything is in good order it will fire on the first hit of the key,if it cranks over a few times and then starts it's not good. Pat

remove the aircon compressor
remove the glow plugs
crack all 4 injector unions at the injectors
remove the solenoid electrical connection on the IP
install your compression tester
crank the engine on the starter, count the number of impulses on the gauge untill it maxes out.
Repeat for all 4 cylinders.

if you gauge explodes at you and youve done all of that, throw it away and go and buy a diesel engine compression tester instead of a petrol one. if you had a diesel engine compression tester you forgot to disable the injector pump and crack the injector unions

NO, you do not do a wet test on a diesel engine unless you like the idea of replacing your gauge. you can do hot and cold

Hi Gerry, perhaps a bit more information on the circumstances and duration of your 'overheat' and the symptoms that lead you to suspect a blown head gasket etc. would help in correctly diagnosing your problem ?


As Pat points out a 300 tdi in good nic will start pretty well start pretty well straight away, unless of course it has crook glow plugs which is a pretty common issue and then from cold it may take a few 'turns' to kick over.


Whilst compression testing is a good way to diagnose cylinder head/gasket problems on petrol powered vehicles as Dave points out it's a bit more complex for diesels.


300 tdi's don't take well to overheating and like petrol engines with overheat gasket failure/head warping they tend to fail in the middle, ie. between cylinders 2 and 3 (four cylinder engine). When this happens the water jacket is usually compromised and the most common symptom is over pressurisation of the cooling system. This can vary in intensity from bubbles in the coolant to eruptions of Vesuvius proportions. The intensity of 'bubbles' may vary from none when cold to major when hot. Coolant/oil mixing may also be present. Coolant may be sucked into the cylinder(s) and show up as steam (white smoke) in the exhaust.


Probably the best indicator of a crook head/gasket is if the engine is using (not losing) water after overheating then the head will need to come off to have a look.


A common cause of 300 tdi overheating is coolant loss due to a failed P gasket, this is often characterised by a reddish brown (rust) stain down the side of the block LHS below no.1 cylinder exhaust port.





The leaking gasket is the wet bit in the top LHS of the picture, the red rust streak is plain beneath.


TIP. Removing the thermostat to help with diagnosis may cause further damage and will only confuse things from a diagnostic perspective.


Deano

Pat303. It pretty much does fire on the first hit of the key but will overheats in about 15 - 20 min of driving. See comment below to see why it overheats. Thank you very much for your time and info and have a top day. See ya - Gerry

Hi DeanOH. I was driving on a Highway out of Albany WA going to Bluff Creek for a day of fishing. I was doing about 90kmh and I smelt something wrong. I checked my gauges and all seemed well. My oil digital pressure gauge and my temp guage were normal and there was an old Toyota van in front of me blowing smoke so I assumed it was that. I was only a few k's from the small of Manypeaks, so I thought I would drop in and use the dunny and have a quick look at my Beast (the Landy D1 that is hahahaha).
I used the dunny and opened my bonnet to check out. I really didn't think I had a problem but found that a heater hose had split. A gash about 3" long and bugger all coolant. I checked my gauges again and my temp still normal. I waited one hour and slowly topped up with water. I decided to go home and give fishing a miss. I had to stop every 15 min to cool down and top up. The gauge was now working as it should.
I think that the water level dropped so quickly that the temp sender didn't have time to respond and stayed at the temp it was when the hose burst. Damn!! that annoyed me.
Yes, it does give water eruptions of Vesuvian proportions, starting off cold with many bubbles and then gushing expensive coolant all over the Beast (the Landy D1).
There is no water in the oil and no oil in the water. Just an over pressurised cooling system and overheating. Thats the story. Any tips and tricks would be helpful as I am not new to working on my cars, but I am no mechanic either. Thank you for your time DeanOH and have a beaut day mate - Gerry (Wedgetail37)

Hi Blknight.aus. That description of doing a compression test is exactly what I wanted. Thanks mate. Great detail and in depth for a Dummy. Maybe you know me hahahahaha. have a good day and thanks again - Gerry (wedgetail37)

i your only looking to prove a head gsket, run it till its warm, pull glow pugs 2+3 then with the valves closed on those pots stick 120+psi in via the glow plug holes. then watch your expanstion tank.

if you're overheating after 10-15 minutes worth of driving and you're not purging the expansion tank then most likely you have some other issue.

Hi Dave, I am already at the stage of where I have loosened the injector unions, removed the compressor, and removed the glow plugs. I have a diesel compression tester kit.
The only query I have is disconnecting the pump electrically. I can only find one wire connected to the pump on the back facing the firewall. is this correct Dave or anybody looking? Thank you - Gerry