I knew my Samurai had some minor leaks from different coolant fittings, so I took it to a shop that specializes in radiator and cooling system repair a couple of weeks ago and had that taken care of. They mostly did a good job, even straightened the fins on my radiator and gave the tanks a fresh coat of paint, and no fittings had to be cut off and replaced. They only forgot that I brought my own coolant and they put the usual cheapo stuff in, so I had to swap that out. Only touched the drain plug and cap since they worked on it.
They also pressure-tested the system and gave me a 16psi cap (up from stock 13psi). Everything looked good.
But a few days later, I noticed that coolant is still disappearing.
I can't find any drips, and I'm really looking out for them. None while it's parked cool, none while it's running, none during cooldown (which is when I used to be able to see regular drips). The cap releases pressure like a soda can whenever I remove it.
There's no milkshake in the oil and no steam coming from the exhaust that I can see.
I took out the plugs after the car had sat cool overnight and cranked it to see if any coolant would shoot out of the spark plug holes, because it does start rather rough, although that is more likely due to carb problems. Only saw a faint puff of what I think was gasoline, it dissipated instantly.
The heater core fittings on the engine are capped.
Any ideas where this could be going? Asked an amateur and pro mechanic about it and both were stumped, the amateur has the same problem on an Isuzu truck in fact.
It's losing 100~200ml per hour of running now. Any ideas?
I wouldn't be shocked if it's ending up in the oil. Pull the valve cover and look for thick, gooey dark brown sludge. You may not get milk from a smallish quantity as it'll evaporate off the water fast enough, but the glycol will still gum up the oil filter and other things.
If I suspect a bad headgasket I'll pressurize the system overnight and remove the spark plugs. Check for pressure drop and liquid in the cylinders.
Grreeeat that would be another severe problem from a <2yo engine...cyl2 seems to be burning a lot more oil than the others too, although there's no smoke from the exhaust.
Edit: Spark plugs I pulled out, in order:
Plug #3 looks awful clean.
See if #3 piston has less carbon too.
You guys may be right, might need a new headgasket & shaved head surfaces 
have a 24hr offroad rally this weekend, I'll just need to bring spare coolant and top it up at every stop (about 4-5hrs apart). Maybe this would be a good time to use some fix-in-a-bottle?
This is why I like iron block engines. Sure they weigh more, but If they get a bit warm they don't immediately melt like cheese. Funny thing is that it hasn't run hot at all recently, but it did a long time ago (failed radiator fan) so I wonder how long this has been going on.
Could it be leaking in the heater core? Maybe just bypass that and see if the leak stops?
Brett_Murphy wrote:
Could it be leaking in the heater core? Maybe just bypass that and see if the leak stops?
He mentioned it is capped off already.
A headgasket on a samurai could be done in a few hours. I'd pull the head and put another one in without the machine work and call it good.
I'll consider just slapping on a new HG, it's gonna be in the shop from tonight to Friday anyway, I'll have to look into all the costs involved. Taking the head off would give a definitive answer on whether the leak is internal.
You said heater was capped.
On many motors you should not cap the heater fittings, it should be looped. Otherwise there is no coolant flow when thermostat is closed. No coolant flow when thermostat is closed means hot spots and steam pockets which will force out coolant while running and seem normal all other times....
I see you are leaning to a head gasket but I will add this anyway. When it is cold there should be no pressure on the cooling system. There maybe a slight vacuum if any coolant went to the reservoir. If there is pressure it could have come from combustion gases being forced into the system.
Well I've got good news, where good means "haven't found a problem and am no closer to a solution"
All the cylinders are equally sooty. Looked down the oil filler cap and still can't see any milkshake in the valvetrain area, or on the dipstick. watched the exhaust closely, had a few drips but they stopped by the time the engine reached full operating temperature, the liquid was clear instead of orangey-pink like the coolant. Ran it on a bone-dry driveway and still didn't find any drips.
The pressure in the system when it's cool is very little, just a slight pop, which I find is common when opening radiator caps in general - if I don't get one then I suspect there's a leak in the system.
Heater core? Hidden up in the car or leaking bypass valve blowing the fluid out on top of the motor?
Does the radiator have an integrated trans cooler?
In reply to GameboyRMH:
I can't help you with your diagnosis directly, but when I had my Sidekick I experienced the exact symptoms you are - it sure seemed like a head gasket, but none of my tests actually concluded it was. I sold it without ever resolving it, but I do remember coming across some threads suggesting it's a common problem, and that changing the HG usually resolves it.
I missed the heater part.
Are there any coolant hoses on the intake? Maybe it is leaking and just evaporating off?
Pressure test it for a long time. When the pressure goes down pump it back up. Place cardboard under the car to find the leak. A leak can spray and evaporate without leaving a trace when the coolant is hot. If the pressure holds during the pressure test then you will have to use UV dye. That will leave a trace where the fluid is spraying.
No heater core is hooked up, and there's no trans cooler in the radiator.
HG was put in October 2014...it's possible the engine has become gooey at some point from getting too hot since then though.
There is one small coolant hose under the intake, it's easily visible and if it were leaking the fluid should hit the ground (haven't seen any leaks from it yet though).
I'll ask the shop working on it today to do a pressure test.
just out of curiosity, how is the expansion tank?
In good shape, no drips out the bottom, hasn't overflowed or gotten low.
When it cools down, does it pull coolant back from the expansion tank properly and keep the radiator full or is the radiator getting low without affecting the expansion tank level? If it's pulling coolant back properly, I'd suspect a small leak that's not a head gasket. If it's not pulling coolant back like it should, I'd be more suspicious of a head gasket problem.
It seems that the radiator is getting low without affecting the expansion tank level.
bentwrench wrote:
You said heater was capped.
On many motors you should not cap the heater fittings, it should be looped. Otherwise there is no coolant flow when thermostat is closed. No coolant flow when thermostat is closed means hot spots and steam pockets which will force out coolant while running and seem normal all other times....
I second this. You should loop those lines.
