qha_vn

I am with my 90 ls400 for 8 years, that same time I have had coolant leak, which cause a lot of problems resulted from engine overheating.

I did a lot of search, brought my car to service center, no one seems have a proper "procedure" to identify the root cause.

every week I have to top up about 300ml of coolant to compensate leak. new water pump set 2 months ago, no visible leak sign.

more than half of my friends (20) got the same issue. no cure?

Tek5

Have a shop do a block test to rule out the possibility of a head gasket / combustion leak since it has been overheated.

They can also use a 4 or 5 gas analyzer to sniff the coolant recovery / overflow tank fumes for combustion gasses they will show up as hydrocarbons anything more than 10 - 20 ppm is suspect, 100 or more ppm is condemnation

If you have access to a cooling system pressure tester leave it pressurized overnight with the spark plugs removed and lightly cover the spark plug holes with paper towels. In the morning check the pressure gauge on the tester to see if it has dropped then just barely spin the engine over and check the paper towels for any signs of antifreeze.
If there is then you have your answer.
If not then somebody needs to look closer or there may be coolant on the ground by now from sitting overnight with pressure?

RA40

iTrader: (6)

If the coolant is not contaminated with oil these are my thoughts on two basic parts:

Reservoir cap, radiator drain **** with O-ring. When the O-ring becomes hard and loses the seal, coolant drips out the lower tube. You'll not see it because this happens when the system is under pressure when warmed up. If that drain **** is old, have a fresh one on hand. These become brittle so when trying to remove it, it may break.

Any other area tends to leave coolant traces like the thermostat, ECT sensor, upper or lower hoses. How old is the radiator? A pressure test would be advised.

qha_vn

thanks Tek5 and RA40, I am just wondering how pressure test can identify where the leak could be. I am sure that there is leak as I have to top up quite frequently.

Finding where the leak is remains a challenge, isnt it?

Largefarva

^the pressure test will put the cooling system under pressure! showing the leak much easier since the pressure wants to escape! and it will find the weak spot. Also, if suspecting a head gasket the pressure test may force the coolant into the cylinders, then when crank king over the coolant will shot out of the hole and soak the towel, proving there's coolant in the cylinders.

qha_vn

ah I see, this is similar to how they test air con system for leak. I guess cooling system test would leave coolant inside (not drain it) and apply (air?) pressure. then check for leak by naked eyes. will they be able to do it with engine stays in place or out?

Largefarva

Yes, coolant remains, engine remains. Its a simple tester that connects to the rad cap mount, then you apply the appropriate amount of pressure (usually 15psi). Your cooling system develops pressure while running, so its usually after a good run that your coolant will leak, due to the pressure.

qha_vn

I see, thanks Largefarva

Yamae

Badly overheated engines tend to have a damaged head gasket as well as a distorted cylinder block. Sometimes the damage is just a little and you don't notice any typical problem. But you should do the pressure test at least.

In Japan, it is very seldom to fix a badly overheated engine these days. The engine is usually replaced. The labor cost is more than a used engine.

Many low milage JDM 1UZ-FE used engines are exported these days and to use one of them is a way to revive the car, but you usually need the original ECU and the cables too.

qha_vn

Thanks Yamae, but in Vietnam they do not allow engine replacement. what a law!

so if I am going to replace the engine, I would need to get it fully disassembled and reassemble on original block with the engine number on it. repair is still the better option :-)

Yamae

I see. Your law is not quite up to date, I must say.
Incidentally, is there any brown substance in the coolant reservoir tank or does the engine oil dipstick have any brownish stuff attached?

qha_vn

let me check but its not easy to tell if there is. the stain may not be obviously visible. I assume this is to determine if head gasket needs replacement.

it is likely because I got engine overheated at least 3 times because of coolant leak issues. I had the head gasket replaced once, but the gasket was not OEM. this may be the cause?

RA40

iTrader: (6)

This video shows a symptom of what a blown head gasket is like from the tail pipe end. The more coolant loss there is, the more steam from the exhaust.

Largefarva

Only one, or both head gaskets? Were the heads sent out for machining, or at least to check for cracks/war page? Aftermarket gasket should be fine if it was installed right and the head was good.

qha_vn

no unfortunately. i was advised that (re)machined would make the block shorter tho very little but it may cause a lot more problems with pistons and valves