Hi everyone.

I'd like to introduce myself as the owner of an 85 range rover with an isuzu 4bd1-t engine and gearbox. It's had a hard life and takes a reasonable chunk of my time and money bringing it back to a respectable level.

I don't know how many of you are familiar with this engine, it's basically an isuzu copy of the cummins 4b1 engine. The problem I'm currently having is excessive oil in the blowby. It is fitted with an oil trap and the breather from there diverts back to the air intake before the turbo. It is recycling oil through this passage at a sufficient rate that the intake tract is continually lined with oil. At idle when cold it is noticably smokey but not when warm.

The engine was rebuilt (bearings, pistons, rings, liners etc) about 18 months ago by me using aftermarket parts (yes, a mistake) which doesn't seem to have helped the blowby, but did improve the performance and starting.

I'm considering building a better oil trap, does anyone have any designs to help me on the right track? But there is a voice in the back of my head which keeps reminding me that other engines don't have the oil traps and don't have the problem.

Just a couple of things:

Sounds like you are positive you have blow-by. Are sure? The intake track can get oil from small turbo oil leaks on the intake side. Intake leaks in turbos are often small enough that you won't notice the usage on the dipstick during a normal oil change interval; nor are intake side leaks prone to show up in the exhaust until they are real bad. A very small leak will coat the intake stream parts though.

Also, is your air filter clean? A really clogged air cleaner will tend to make the turbo suck air out of places it normally wouldn't. This is a real long shot but I have seen it in the older GM diesel (aka "blower" motors) ag engines.

These two tips are all I have since I not experienced enough with that particular engine to offer more without straining my credibility.

Good luck and wish I could be of more help,

NCDiesel

Sounds like the standard Isuzu diesel breather problem.

Some oil catch can hints at:

http://clubisuzu.proboards29.com/in...mp;action=display&num=1099954151

Thanks for the info, especially on the oil traps.

My air filter is clean and I'm very sure it's oil from the blowby and not the turbo. The oil is easily found in the tube from the trap to the intake before it hits the turbo.

If you re-route the blowby hose to an external catch tank (say, for example, over to the passenger-side corner up against the firewall), don't send the line back to the intake. Cap that hole off (so air isn't suck in through there, because that is post filter remember). Instead, vent the tank with a hose fitted with a lawnmower fuel filter. That will allow air to come out under pressure, but hold back the oil.

One of the weird things about the blowby is that there is less (if any) if you don't send it back into the system. This lead me to think a long time ago that the return system the Isuzu engineers thought up actually sucks more out. When you think about it, that return line isn't that far from the turbo (closer to the turbo end than the air filter end, anyway) and I reckon the turbo just sucks it out. My old 4JB1 was a blowby factory until I stopped sending it back.


--Bighorn--

Hi Dougal, first of all, Aftermarket parts are fine as long as they are from a reputable supplier and are fitted correctly.

I used to work for a tractor agency and never had a prob with after market parts, same with trucks.

Try a change of oil brand and check the ash content of the oil, I know modern Jappers need a high ash content oil, check with your local isuzu truck dealer as well on that one because the 4bd1 is used on some of the smaller trucks.

I have always been dubios about recycling the blowby back to the motor, I used to have a turbo'ed 3b motor in land cruiser and the intake hose used to get wet with oil. I reckoned the intake was having a venturi effect on the gasses so I just piped it to atmosphere with a non-return valve in it.

Turbos are very fussy about good quality, clean oil because of their high speeds and Ive seen a brand change cure a few probs

Another thing you can try is to run the vehicle on a chassis dyno and while its under a good load and the turbo fully spooled up, check to see if the hose from the air cleaner to the turbo is constricting or do a power test with and without the air cleaner element in.

cheers

On the weekend (while pulling the engine out to change the front gearbox seal) I had my father unbraze the oil trap. I packed in three strategically placed (stainless) steel wool pads and it has helped enormously. Thanks to James Whyte, I picked the steel wool gem from those links above.

I haven't removed the intake hoses to check, but the blue smoke at idle when cold has gone completely. I'll be taking the piping apart next week to tap in some pressure/temp sensor lines (I can't help myself) so that'll be the final check.

I'm happy with the aftermarket pistons/liners/bearings. But the gasket/seal kit was a mistake. I've since replaced both front and rear crank seals with isuzu items, many gaskets didn't fit and the head gasket just looked awful. It has held so far though.

I'm still curious as to why isuzu's have such excessive blowby and why they need oil traps to not blow blue!

FWIW, this is not brand-specific... most motors use a convoluted-mesh (sorta like steel wool) before the PCV valve. On my 302, it is at the back of the intake manifold.

Randii