Thread: How to compression test a 300tdi

Hi again Deano. I drove 5-6 minutes before I stopped at the local town dunny. I really didnt know it was hot. No lack of power, gauges ok. I have already bought a unit which I still have to fit. It was from Ebay and consists of a a temp control unit, a buzzer and a 2 metre temp probe that fits directly onto a bolt on the head. - Gerry

Thanks mate, I will have an answer in a hour or so. Got to take Mum a new phone to her Nursing home. When I get back I will do the test and post the results for all to see and comment. I will then have an idea as of to the condition of my motor. Luckily, I have another D1 (1994) I bought from a mate and the donk seems to be ok. I can get a few parts off it, such as: bullbar, spotties, snorkel etc etc

Hi Guys. here are the results of the compression test on my 98 D1 300tdi.

Cylinders: 1. 360 2. 350 3. 360 4. 380

So, what do ya reckon?? - Gerry

ps. See above for reason for overheating

Hi Gerry, got this from the difflock.com forum.




Service repair no - 12.25.01
1. Start and run engine to normal operating
temperature.
2. Switch off engine.
3. Disconnect spill return hose and fuel pipe from
No.1 injector.
4. Remove retaining nut, release clamp and
withdraw injector from cylinder head. See FUEL
SYSTEM, Repair, injectors
5. Disconnect electrical lead from fuel cut-off
solenoid at injection pump to prevent delivery of
fuel to injectors. On vehicles fitted with a digital
diesel shut-off valve (DDS) immobilisation
system, disconnect DDS multi-plug.
6. Ensure injector port is clean, If necessary, crank
the engine a few revolutions to remove any
loose carbon.
7. Fit dummy injector, from diesel compression
tester kit LRT-19-007, into the cylinder head and
clamp securely in position.
8. Connect flexible hose and gauge to dummy
injector as shown above.
9. Crank engine for 10-20 seconds and note
reading on gauge. The gauge will indicate the
compression of the cylinder and maintain the
reading until the pressure release valve on the
gauge is depressed.
Expected readings of a crank test, with vehicle
battery fully charged, compression ratio 19.5:1
should be 24 bar (348 lbf/in2



At first glance from this information it would seem that your compression readings are all good but I don't believe it, how else do you account for the obvious pressurisation of the coolant ?


Step 1 is very important here, did you run the engine up to temp. before testing ?


From a theoretical viewpoint the thermostat could be stuck in the closed (bypass) position where the radiator is excluded from the cooling system which would give similar symptoms to what you have. In this case the coolant over pressurisation would be due to boiling of the coolant as opposed to over pressurisation due to fuel/air mixture being forced into the water jacket. Pretty easy to check though, is the radiator getting hot ? or remove the thermostat and heat it up on the stove, does it open ? Has the water pump failed and caused the heater hose to burst as it fills with steam (highest point in cooling system) and no water is being pumped around ?, again pretty easy to check.

All of the above is possible,but for my money the most likely scenario is that the heater hose has burst because it is old and soft ( just like me ) and the result due too loss of coolant and overheating is that the head gasket is now shot and possibly the head as well . 5 - 6 minutes is really a long time for an alloy head engine (especially a 300 tdi) at operating temperature to go thirsty, I'd really like to be wrong here and check the above cooling system items first, but I reckon the head needs to come off for a look.


Deano

Hi Deano, first of all I would really like to tell you I am very appreciative of you help. Thank you so much. I buggered up and didnt warm up the motor before checking the compressions. I will definitely check the thermostat first. I have already replaced the pump and the 2 gaskets plus the heater hoses. I think I will check the thermostat as you described in boiling water on the stove. Then if that is ok, I will take off the head and inspect it and have it tested. I will not do another compression test as I agree with you. When warm it will only confirm what you and I both think. I will save the time because if the thermostat is ok then the problem surely must be internal. What do you think about my decision Deano? Thank you again - Gerry

Hi Gerry, I agree.


I was going to suggest in my last post that you could refit injectors/glow plugs and bleed the fuel system, run the engine up to temp and re do the compression test, but realistically I think we both are pretty sure what the problem is and as you say it's internal.


Yes it could be the thermostat and that would be a gift from the gods if it were so but I reckon it's pretty unlikely but 'Murphy's Law' means it needs checking out anyway. Boil up the thermostat and check its operation out and have a close look at the bulb for shiny rub marks. Probably worth replacing regardless as they are a consumable item. Make very sure it's a bypass type thermostat of the correct size as this is critical to correct cooling.


Take your time and check out the viscous coupling and its bearing for smoothness. It may be worthwhile changing the coolant expansion tanks pressure cap as overpressure can 'bugger up' its pressure relief valve. With the fan belts off give the idler/tensioner pulleys a spin (3 off) as it's a monty that at least one of them will be a bit 'graunchy' , and at around $2 a piece from your local bearing service (they're all the same bearing) worthwhile changing them all. Have a real good look at the P gasket as these are a major cause of grief. I've rebuilt (top end) three of these 300 tdi's, all cooked because of failed P gaskets.


Anyway "off with its head" and have a real good look at the head gasket particularly between 2 & 3 to the water jacket, it doesn't take much of an imperfection in the head gasket to cause 'blow by', also take note of how many holes in the corner tab on the head gasket (denotes thickness) as you will need to know when ordering a new one.


For the head I lay a 2 thou feeler gauge (thinnest in the kit) between cyl 2 & 3 and lay a straight edge (I use a steel rule) across it lengthways along the head. You should be able to rock the straight edge like a see saw, if not it's warped, lets hope this isn't the case but I'd be surprised if it wasn't warped.


Good luck.


Deano

PS. Be careful when lifting off the rocker gear as it's real easy to lose the little 'cups' that fit over the ends of the valve stems.


Deano

Deano, there is so much info in your last message that I didnt know (corner tabs etc) but I will follow to the letter. I have a Feeler gauge and I will buy a 3 foot straight edge (steel ruler) tomorrow or monday to do the warp check. I will order all parts from Roverlord as I reckon they are fair and honest. I used them to buy the pump, hoses and gaskets. if I am extremely fortunate it will be a faulty thermostat but I wont hold my breath for that one. Thank you for your time so late at night for you and have a very pleasant night. Goodnight mate - Gerry