He is checking for a cracked head where combustion gases are finding a way to the coolant hence the hard coolant line ober night. 100 psi is used to make hearing or seeing the leak more pronounced.

??

Please read up leak down test. If you see bubbles at 100psi the head is a goner and I doubt the car can be driven as described by OP. What is the pressure when combustion happens?

Did the engine see a lot of heat? Because if it didn't the head isnt just going to magically crack. You probably just have a bad head gasket. I'm so confused on your post as well.. Why are you concerned about pollution? It was good in its time, but with all the green freaks and modern cars it's most certainly not up to standards. But if that's your concern, I wouldn't mind buying an SDL if it's clean otherwise. ;)

Sorry for my poor English attempt to express the situation,

I am probably better with my hands,

I am debating/hesitating before I take the head off, check to it my self,(gasket, visual ,straight edge,),

if I want to spend the money, and take it to Metric, in Canoga Park,Ca,

Car did not heat, in the last 150,000 miles I drove,

Once it drives, it loves the 70-80 miles, for hours,

only at night time it gets the hard radiator hose being hard,

Few days ago, it stop happening, NO hard radiator hose,

I change the coolant Tank cap, and the pressure came back, and made the hose HARD,

Could not see any wrong with the old cap,

but it leads me to believe, that the combustion gases are penetrating,

Time to take the Cyl. head off,

Thanks for your kind input,

It helps,

Long way for clarity,

Lisle 75730 is labeled for Diesels. 75630 isn’t.

https://www.amazon.com/gp/aw/d/B000I16L90

But you mentioned red fluid which is for Diesels vs blue for... it doesn’t say.

How did you get test fluid into the combustion chamber? There is no engine vacuum to draw it as the instructions suggest.

Sixto
98 E320s sedan and wagon

it says diesel on the bottle
 

it says diesel on the bottle,

One temporary trick is to leave the pressure cap only on the first latch, not fully closed, so cooling system cannot build pressure. Cooling capacity is reduced so watch the temp gauge but coolant can flow better because the pump isn’t fighting full pressure all the time.

Sixto
98 E320s sedan and wagon

it is Lisle 75730,

I think I will put the old cap back, till I fix the problem
 

I think I will put the old cap back, till I fix the problem

Thanks Sixto

Please listen to 40 + years of experience building engines. Any experienced engine guy knows what I'm talking about. A leak down test encompasses more than just piston rings.

We don't care about leak down percentages in this case, just if the air ends up in the cooling system.

100 PSI is typical and plenty in finding a combustion chamber to coolant leak that means anything. In fact, if you get a cylinder head pressure checked at a machine shop, they to use 100 ish PSI.

I generally fill the rad to the top then look for the level to rise. If the level goes up, there is a slight leak. Bubbles are a sign of a larger leak. I've worked on engines that used a qt of water every 4,000 miles, when doing a leak down, the level would slowly rise. A qt every 4,000 miles is very slight and the leak down test found it.

Any rise with a pressurized cylinder = combustion chamber to coolant leak. This could be from a failing head gasket / cracked head / cracked cylinder.

Thanks for the enlightenment. What i meant is seeing bubble is very serious. Is a qt every 4000 miles acceptable? I really don't think the OP has a serious issue and warrant a head removal, IMHO.

thanks a LOT for your response, and input,
 

I do tend to agree with Ah-Kay,

The car drives like lion, love 70-80 MPH, climbs hill,

Turbo 12 psi,

No loss of coolant.

Filled the coolant tank, till the top, NO bubbles, no change in coolant level,

While engine is idling,

The pressure in the cylinders is almost 2000 psi,

So why should push 100 psi, down the injectors, to see bubbles,


Still hard radiator hose in the morning,

Might go tomorrow to a shop with combustion sniffer,

Live and learn,


Thanks for your kind support,

If leak is so minor, maybe re-torque of the head,
 

If leak is so minor, maybe re-torque of the head,


Might reduce the leak,

Don't touch it. Just enjoy the car.

the saying here applies.. "if it ain't broke don't fix it"