Need suggestion for a mysterious coolant leak

[Bud Tierney]

Without reviewing whole thread, the "jump in cold car, bound down highway=no appreciable loss, while jump in car, tootle around doing errands =loss, does sound like something cracked, or not sealed, when all cold/contracted, that expands, sealing itself up, when mass of engine/head hot/expanded (already included in speculations above) ...

May well require pulling head to find... personally, I'd be inclined ti try stop leak first, in hope will seal during moderate temp periods (cold enough to leak but warm enough for sealer to bond)...

[fzslg]

6 hours ago, Bud Tierney said:

Without reviewing whole thread, the "jump in cold car, bound down highway=no appreciable loss, while jump in car, tootle around doing errands =loss, does sound like something cracked, or not sealed, when all cold/contracted, that expands, sealing itself up, when mass of engine/head hot/expanded (already included in speculations above) ...

May well require pulling head to find... personally, I'd be inclined ti try stop leak first, in hope will seal during moderate temp periods (cold enough to leak but warm enough for sealer to bond)...

Thanks for reply. There are some more important clue, it can pass pressure test no matter engine is cold or hot and running or not, in the first half hours after start engine the coolant system pressure is much lower and building up more slowly than other cars.

It seems coolant is leaking only after engine start and when engine is running at low rpm. Where the crack could be? Exhaust valve?

[Spinneyhill]

If it were leaking into a cylinder, it should leak while sitting, cold, because the crack has opened up with contraction?

 

How do you measure coolant system pressure?

 

If the pressure comes up slowly, I would wonder if it is warming up fast enough, i.e. is the thermostat stuck open?

[fzslg]

3 minutes ago, Spinneyhill said:

If it were leaking into a cylinder, it should leak while sitting, cold, because the crack has opened up with contraction?

 

How do you measure coolant system pressure?

 

If the pressure comes up slowly, I would wonder if it is warming up fast enough, i.e. is the thermostat stuck open?

I bought a pressure tester. When it is sitting and cold, it can hold 18 psi for couple hours. It seems no leak while sitting and cold.

I connect pressure tester to recovery tank and start engine with no pressure. Like other two cars I checked, engine takes 20 minutes to warm up and thermostat opens.

But after thermostat just opens, the pressure read on my car is lower than the other two, and it needs maybe 20 more minutes idling to reach the pressure read on other two cars.

[trini]

To check to see if water is getting into  the engine oil take a few ounces  from the sump, put on a tin sheet and heat underneath with a torch. The water will pop under heat. If that is the case  the problem could be a leaking head gasket or a cracked head . Read up on Rusty-OToole.

[fzslg]

Finally, it is an internal leak. No.1 spark plug is little bit rusty, and after head was removed, I saw No.1 cylinder chamber is cleaner. It should be the head gasket, but the mechanic said head still needs to be tested to see if it is cracked or warped. Also I ask mechanic to change timing chain and water pump by the way, almost no additional labour cost.

Thank all of you again for suggestions and support, very kind of you.

[trini]

Replace the thermostat while you are it. Also good idea to boil/clean the rad at this time

[fzslg]

17 hours ago, trini said:

Replace the thermostat while you are it. Also good idea to boil/clean the rad at this time

Is the high flow version thermostat better?

[edinmass]

Do a CO test on the coolant to check for exhaust gases entering the coolant system. The kit is available over the counter. Use a bore scope to look in each hole after you pull the plugs, if you find a clean piston and head thats your problem. I have seen very, very small leaks from hoses that just drip onto a manifold and evaporate the coolant leaving no trace. Sometimes you just have to drive it till it gets worse. The CO detection kit is very helpful on head gaskets and cracked heads.......its not effective for other leaks. Ed

[trini]

I do not know of high flow or lo flow. Thermostats comes in different heat ranges. My 28 Dodge senior carries a 150 degrees thermostat. Although there is a machined seat in the thermostat housing,,size nearly 2 inches in diameter these are not readily available.  I installed one inside the top hose.. At first it would not go into the hose so I boiled the hose in water for about ten minutes. The thermostat went in like a breeze. My 1995 Cherokee had a slow  coolant  leak  which was difficult to find. After a hot run I noticed around the lower hose connection was damp. This was happening frequently , the coolant vaporising . There was a buildup of crud  between the hose and pipe.