[Jimny_No_Power]

Hey guys & girls,

I've got a coolant leak on my '01 m13a Jimny.
I'm trying to narrow down the cause to internal/ extenal before I go pulling everything apart. Any advice on what to check and look for would be really helpful.
Initially suspected rad cap, but having replaced that and considering the air I've found in the system, I think it's blowing out air + coolant out the cap, which is why it's not "flowing " to the expansion tank.

Symptoms:
It leaks only when being driven, there is coolant on the underside of the bonnet, on top of the radiator, spray on the engine most above and to the right of the fan. No evidence of a split hose, water pump seeping or rad core damage (haven't been able to check seams yet). Losing about a litre a week. Draws from expansion tank, but appears not to fill it back up. Even when there is fluid in the expansion tank, the rad appears to be approx 1" air at the top.
No incidents of overheating as yet, but then again, the dash temp sensor on these is primitive. Also, there's no pressure when it's hot and I remove the cap :/

Replaced so far:
Thermostat, expansion hoses, rad cap (aftermarket and OEM).

*getting fed up*

[Jezza86]

Head gasket.

[alien]

Head Gasket. Done the same on mine twice in the last 18months with g16.

On mine it has now gone twice between cyl 2 & 3 - runs around the bore on cyl 2 for about 90 degrees, then shoots off towards a coolant gallery and over to cyl 3 from there. It pressurises the coolant and sends bubbles out the overflow bottle.

If you have a sniff of the overflow it probably smells like petrol, and there will be a residue in the overflow bottle too.

Given summer is on the way you're better off sorting it out now rather than driving it and risking turning the engine into an anchor. Ask that when it is rebuilt they not only skim the head (i had 3 thou taken off mine) but also hone the block to be super sure.

[Jimny_No_Power]

Thanks for the replies.
I had a look at it this evening.
With the rad cap off, there doesn't appear to be much normal circulation going on when I rev it up (~2500rpm), That said, the top inch of the rad was "air" and it tended to belch coolant out of the rad cap hole rather than a surge. The top rad hose did have coolant in it however.
No coolant/ oil mix and no obvious exhaust smell in the coolant. Coolant hasn't been entering expansion tank, I think this may be because the "belching" has forced gases and coolant out of the cap, rather than it flowing with a constant pressure down the overflow hose. No obvious bubbles at idle.
Water pump bearings are shot, judging by the amount of play in the shaft with the fan off. No signs of leaks from the weep hole.

Lastly, did a quick compression test twice through: 1(front),2 & 4(back) were all close to 175psi with three cranks, no° 3 was 130-140 psi.
I'll do 4 tests on each cylinder on this weekend just to confirm, but I'm guessing this all suggests cylinder 3 is pressurising the coolant system due to a blown head gasket?

Thanks again fellas.

[Jimny_No_Power]

Regarding the honing of the block- I'm doing the gasket replacement at home, so I really don't want to pull the whole block out and take it to a machine shop too. Is it absolutely critical?

[alien]

Well, the first time mine was done the block wasn't touched, but 18 months later it failed in exactly the same way, so this time around the block was done as well just to be sure. Still cheaper than replacing the engine.

[jdk81]

Did you do a wet compression test?

You can just replace the gasket (i've done it plenty of times).

Be careful of which brand you get, the 16v engines are a total pain in the arse if the head requires a retorque. I have had to retorque every headgasket i got off ebay in the kits, and even one from suziworld

[Jimny_No_Power]

Hey,
I've just got back to Brisbane and managed to do a wet test. Added approx 30ml of oil to the cylinder and compression readings went absolutely bat shit. Like + 150psi each crank. Oil got into the tester gauge, but came out and I retested (dry) the other cylinders to be sure.
Wet tested several times and always off the scale (> 300psi) on second crank.

Any ideas what this means? I'm new to compression testing my cylinders

[jdk81]

30ml per cylinder is way too much oil.
That's about the volume of space in the cyl/head at tdc.
No wonder it pumped oil into your pressure tester.
It's possible to break stuff or prevent the engine cranking, if it hydraulics.
Any results from a wet test with that much oil aren't hugely helpful.

About 5ml (a teaspoon) is about the max you put in.
Its just enough the keep the rings wet.
If it reads low when dry, and high when wet, it's the rings etc.
If its low-low its the head/valves.

[Jimny_No_Power]

Thanks for the heads up. I've put it back together and it's on the road until next week when I've got a few days off.

I read online amounts of between 5ml and 2oz (~60ml), so I went in the middle, but yeah figured after that was probably too much. Will test again and repair next week and let you guys know how it turns out.

Thanks for the help guys