Possibility of HG leaking?

weasel318

Registered User
Sorry if I am making too many threads, just thought it would be more organized that way since its dealing with different issues each time? If its too many threads let me know! Sorry and thank you!

Anyways, I just did the oil change, fuel filter change and coolant change. I am bleeding the cooling system and have idled the car close to 30-40 mins. The first few times the thermostat opened there was a big bubble and then coolant went down. Now after the fifth and sixth time of it opening I noticed I was still getting bubbles only after I throttle the car? The small bubbles was consistent with the rhythm of the throttle. I am guessing I have a leaking HG which only leaks into the coolant when the car is above idle RPM? Or is it just that I didnt bleed it long enough? Or are these cars tricky in terms of bleeding the cooling system and regardless of how long you bleed there will still be air/bubbles trapped in the system? I am guessing Its a leaking headgasket and its leaking only when power is applied but not at idle?
 

35th

Registered User
Have you done a cylinder compression test yet? If not that's what I would do if hg is the problem you should have at least 1 cylinder that's lower compression than the others
 

89SupercoupeSC

Registered User
I just changed my waterpump and it does take quite a while to bleed the system. I think 30 mins of idling is not enough. Just drive it normally for a couple of days and check again for bubbles.
 

weasel318

Registered User
35th, I would but from looking at how its running I dont think it would work? The leak down would only tell me my rings are good or bad. The thing is when its idling there isnt any bubbles. I can let it idle for a good 10 mins at idle rpm without a single bubble coming out. However once I rev the engine for a few seconds the bubbles appear. I can make a rhythm out of it, If I rev it for 2 seconds with 3 second breaks in between the bubbles will show up for a few seconds, stop then go again after ~3 seconds. I think the crack in the gasket or head or engine is only show up when there is a "load" on the engine. With just regular pressure from a leak down test I dont think there is enough pressure to open up that crack. I am guessing it only leaks when combustion pressure of 300+lb is available. Block tester test came back negative when I was idling, I didn't rev it because I the test never said anything about that.

I have idled it for a good 2 hours now, same song and dance. My mechanic said its the headgasket and the pressure has to be higher than at idle for it to leak.

Also if I am getting bubbles from bleeding, coolant should be going down in my bleeding tool to take up the space the air was in the cooling system. Thats not the case currently, the bubbles come up and the coolant level stays the same. So from these few observations its definitely combustion gas and not air bubbles I think.

And usually air bubbles are bigger and randomly surfaces followed by the coolant level going down a bit. In this case the air bubbles are constant without any lowering of coolant.
 

sam jones

Registered User
This is my experience with coolant system on a neglected car. This is under the assumption all prior owner overheating issues have been address.

The supercoupe is notorious for trapped air and or engine hot spots during bleeding/purging. Again this is what has worked for me.

Eliminate potential component failures.

New Water pump.

New Radiator cap.

New pulley and belt.

New traditional thermostats (no Fail-Safe types).

New upper and lower radiator hose. Replace the bypass hose at the thermostat housing.

New coolant temperature sensor.

New gauge sender. Note. There are 2 types of senders. The black ring sender is for analog instrument cluster (supercoupe). The green ring is for electronic cluster (1989 - 1993 lx).

Checking heater core hoses.

Clean coolant recovery tank. Check for cracks at the mounting points. Check the recovery tank hose.

Sleath leaks areas include the coolant oil cooler, heater core throttle body heater and the "J" hoses going to the coolant sensor fitting to intake manifold (if equipped) that have swage connectors.

Make the decision for the radiator.

The original should be removed and sent to professional radiator shop for the core. to determined if serviceable.

or

Replace with new radiator . If possible spend the money a high end aluminum unit.

Preparing for bleeding/purging.


Jack front of car and support with jacks. The purpose is give the trapped air a direction to be released.

Service the appropriate coolant mixture in radiator.

Service coolant recovery tank to FULL HOT. This will be your indicator of how much air is in the system.

Put the HVAC control to vent, fan to high and select to hot.

I connect a Scanner to read coolant sensor temperature.


Bleeding/Purging system.


Start car. Check for leaks. Run for 1 hour.

Bleed air from thermostat "stand pipe" housing bolt.

Observe both gauge and scanner reading while ensuring fan operation starts and stop and the approximate temperatures.

Observe heat venting in cabin. If you notice the temperature fluctuating from hot the cool to hot there is an in the system.

Shut down car.


Check servicing I wait 6 -24 hours. Do not remove radiator cap at this time. Check and correct any external leaks.

After this rest time check the recovery tank. The coolant should be much closer to or lower than the FULL COLD mark. Check the radiator. Top off if below recovery tank to FULL COLD or slightly above.

Repeat the Start Car procedure again.

If both the recovery tank and HVAC is good consider the idle bleed/purge good.

Remove car from jack stands. Check recovery tank. Check/Service to FULL COLD or slightly above on level surface. Turn HVAC control vent to cold and fan off.

Drive car and monitor. Top off if required. Might take a couple of days of drive cycles to remove remaining air.
 

35th

Registered User
I wonder if that's my issue as well I've done everything but that process and after driving a distance of let's say 45 mins my coolant will be low I'm gonna try that and see but what I was saying about compression test I wasn't saying a leak down how much compression per cylinder do you get should be pretty even across all 6 cylinders if it's not that's a problem
 

weasel318

Registered User
Sam jones, good advice! But for the new parts list, none of those things will cause a constantly bubbling of the coolant when I rev the engine would it?

I ran the car for more than an hour already with the front end jacked up to bleed. Basically ran it 1 hour non stop, cooled down for the night, ran it again for 1 hour mins, cooled down for the night and ran it again for 20 mins todays. Same song and dance. Bubbling only when revved, and with the bubbling the coolant doesnt go down. If that much air was being displaced the coolant should be going lower but the coolant level has stayed the same height. Thus its probably headgasket.

Also the heat is blowing hot after the first 30 mins of bleeding, it was cold the first 10 mins, but after that 30 mins of bleeding it was hot and stayed hot.

The recovery bottle has alot of dirt in it, im starting to think that it might be carbon from combustion gas.

Also the compression test is sort of more worthless than leak down test, no offense. The compression test just shows if it will have compression or not. If the engine can make compression faster than how fast the leak is (the leak has to be small) then the compression will come out fine. My explorer with the 4.0 ohv had a blown headgasket that was pretty obvious, the tail pipe was blowing out a white smoke screen. If you open the radiator the coolant was rising and falling from the combustion gas. Even with the headgasket that bad, the compression tester still showed that my explorer's 4.0 engine had good compression (~135psi) for all cylinders. The test was done with all spark plugs out and the radiator cap off. In my case the cylinder was able to make compression faster than compression was leaking out into the cooling system.

After that explanation, i think the compression test would be useless here because in this case the headgasket is only leaking when there is a spike in pressure in the cylinder(s) aka when I rev it. So it will probably build up pressure just fine and show a constant psi throughout the cylinders since the motor was idling fine, was revving fine.

Im already tearing it down to change the hg. Thank you for the advice guys!

35th, how many times has it been low? And how many times have you added coolant? in total how much coolant do you think you have used?

35th if it seems like a HG problem I would get it addressed before the leak between the combustion chamber and cooling passage gets pitting done to the block, head, or both. If that happens to the block you have to do an engine out instead of just headgaskets because in that case you will have to mill the block.

Also found a few new problems, will make a new thread about it.
 

35th

Registered User
On going issue for quite some time very odd really sometimes it'll go months with no loss of antifreeze sometimes it does more like it has recently where it's a constant loss but another factor could be I don't drive it often and when I do it's typically not far I seem to notice loss on further trips no antifreeze in oil no smoke no wet spots in the engine bay or under the car just vanishes into the nothing
 

weasel318

Registered User
Might be headgasket? Does your motor oil level rise? If not we can rule out the timing cover I think. If its lose coolant slowly, its probably a slow leak at the headgasket. Where mine might be a slow leak, but for sure my leak needs to see real combustion pressure above idle to open up the crack (wherever it is) to allow combustion gas into the coolant. At idle, I can idle it for at least 30 mins without a single bubble. I can also do a thing where I hold the RPM at around 850 RPM for around 10 seconds, then wait for the thermostat to open, when it does the Gas bubble would be huge. In this case the combustion gas isnt enough to blow pass the thermostat hole, but its enough to build up behind the Thermostat, so when the thermostat is hot enough and opens, it lets this big air bubble out. But this is just purely from my observation. And Its not an air bubble from not bleeding long enough because everytime I had a big bubble come up the coolant level in my bleeder would lower by alot, in this case it shows up as a big bubble but the coolant level stays the same.

Mine is most likely a headgasket so I am tearing it down as we speak lol. Ford and their engineers hiding bolts everywhere, where you cant reach them LOL

My Explorer had the same thing as your SC. It would slowly lose antifreeze. But it wasn't much. Probably had to add less than a quart over 3k miles. Then slowly symptoms started to show up.
 

35th

Registered User
You might be right I probably need to do a headgasket but trying not to because I'm building a 302 to swap into it tired of chasing issues with this motor it's been 3 or 4 years of it constantly failing everything from Harmonic balancer to every sensor on it and still has issues gonna go 302 full carb and be done
 

35th

Registered User
So just did the air bubble thing jacked car up ran for an hour bubbles coming up each time tstat opens and after an hour I shut it off and it bubbled for 2 solid minutes after shut down not a good sign recovery tank is near overflowing even though I only filled it to full when hot
 

weasel318

Registered User
Did you have the heat on? I am betting the combustion gas is filling up the heater core and forcing that volume of coolant into the reservoir. Youres might be worse than mine LOL . Do a headgasket and enjoy it. I have enough 5.0/5.8/2.3turbos so I am just going to rebuild this one and try it out. I do want to find a 5.0 sport one of these days just to have it lol I have an extra junk SC in my backyard that I am thinking about doing a Mustang swap into. But I havent found the right shell yet. I want a yellow 94/95 mustang but they are so rare to find especially in the 500 dollar price range LOL. Im cheap......

But yea, you should do the headgasket along with me. We can be headgasket buddies over the internet. :D
I am partway through tearing down. Trying to figure out the AC dilemma. Not sure if i should disconnect AC or just move it to the side.
 

35th

Registered User
When you get your head gaskets off and find where it's leaking could you post a pic of it
 

weasel318

Registered User
NOOOOOOOOOOO! Im jking :p Yeah I will post a pic of it. Hopefully its the HG. Im hoping its not a cracked head or block. Have a higher chance of cracked head right now because of the symptoms... :(
 

35th

Registered User
I think I'm finally gonna tear mine apart and do them which is a pain cause I'm building anothrr motor for it but it'll be awhile before I'm done with it and as summer heats up just gonna make it worse all the way around so....
 

35th

Registered User
No I pulled the motor because harmonic balancer broke and had leaking oil pan front main seal timing cover was cracked so pulled it to correct all the above definitely kicking my self in the rear for not doing HGs at that time but they are both off now and gonna take them up to a local shop and have them resurfaced cleaned and pressure tested next wends then the following wends day will be re assembly....
 

35th

Registered User
How far along are you on yours? Both of mine are off started at 130pm and was done by 430 then 2 more hours of cleaning up tools and what not that it was much quicker than I anticipated
 

weasel318

Registered User
I just have the lower manifold, heads, and exhaust on. Everything else is out of the way. I feel bad now :( since mine arent off yet LOLLLLLLL. But then again I labeled and bagged everything in case and mess up. Not gonna lie, the stud holding the rear coolant pipe on made me spend 2 hours taking it off. Also a few fasteners were in WTF locations lol. It looks like my car has never been touched before by a mechanic? Like the front timing cover and WP has been changed but everything else on the car looks like it has never been apart? One weird thing though was the exhaust studs vs bolt location was way different than what the shop manual specifed. The order of it resembled more of the NA version of the motor compared to the SC for some reason.

I can see why alot of mechanics refuse to work on these things. My Explorer 4.0 OHV was super easy to tear apart compared to the TBird. Hopefully I will have everything apart. Now the challenge is finding a good machine shop in the LA/OC/IE area.

Also did you find out where it was leaking from?
 
Top