weezel77

Hello, my name is Matt. To start things off I have a 99 mustang gt, 160K miles. The issue i have been having is the coolant keeps burping out of the reservoir. I did in fact bleed it completely and correctly ( multiple times now...) I have put a new reservoir, cap, hoses, radiator, thermostat, and water pump on it and it still does it. If its cold it will do it almost right away (needle has barely moved). If I let the engine heat up to optimal temp and bleed completely alot of the time it wont do this if at all a little bit. Let it cool back down and it will do it bad again. No milky oil or oil in the coolant either. I did a compression check and all cylinders were between 160 and 170. I pressurized the coolant system to 16 psi and it held for hours. I also did a block test on it and the liquid never changed color. I can not figure out if it could possibly be a head gasket since I would think one of the above mentioned tests would have failed. Not sure what else I can do to figure out whats going on. There is no visible leaks of anything anywhere and no steam coming out of the exhaust. Any and all suggestions would be very appreciated and thank you in advance.

Derf00

So you are still getting air into the system after bleeding? Leak down test would be the only other thing I could think of to rule out engine entirely.

I'm not completely familiar with the SN95 GT cooling systems. I had an 00V6.

When did you start having this problem?

Is there a coolant line running to the throttle body on this car?

weezel77

Thanks, no there is not a coolant line to the throttle body that Im aware of. It started one day i was out to dinner with my fiance. I was going down the highway and I luckily looked down and seen it started to get warmer than normal temp. Got out opened the hood and there was brown rusty looking crap all over the place. I let it cool and filled it up and babied it home. Flushed the system about 4 times before it would come out clean. Im not sure the root cause but as nasty as the coolant looked Im thinking it may have just clogged up or couldn't flow good enough to keep it cooled down. im just thrown off at the fact it does it WAY worse when its cold. I would hate to tear the motor down and spend that money if its not a head issue or head gasket issue. Thank you again I hope to figure this out i hate not being able to drive it.

Derf00

Could be a plugged radiator then if you had that much brown gunk flowing out. The passageways in the radiator are very small. It doesn't take much to plug them. If enough of passageways are plugged you can end up with fluid back up into the reservoir which sits up top. Drain your coolant, disconnect the top/bottom hoses, take a garden hose and fill it from the top hose letting it drain out the bottom, the flow should never back up. You could try flushing out the radiator with a chemical flush but make sure it's an aluminum safe flush.

weezel77

Thanks again and its worth the effort since its easy enough. Im not sure if it would be this since it does it worse before the thermostat opens tho. Ill be doing a leak down test this weekend at some point anyways so depending how that goes i will flush the radiator for the heck of it anyways.

Z28KLR

Based on your description of the issue in the first post, I don't think it's the problem.... But since I saw no mention of it and nobody asked, is the cooling fan working?

I have a very similar issue with my '08 Explorer 4.0, been doing it for a few months now. Might drive fine for 50 miles and then starts overheating and puking coolant from the reservoir. After replacing a few cooling system items that needed attention anyway, and throwing a couple more parts at it just for fun I did a block test and of course the results came up (the bad kind of) positive. Other than overheating occasionally it runs fine.

I know you already did a block test and came up with negative results, but if it were me I would be tempted to repeat that test again.

Cooling systems are pretty simple. If there's sufficient coolant, flow of coolant, and airflow through the radiator then all should be good. Based on your description and my own recent experience I think it very likely that exhaust is getting introduced into the mix. Leak down will confirm a leaking exhaust valve (only that it's leaking, not necessarily where it's leaking into), but if done correctly the block test should absolutely confirm the presence of carbon in the cooling system.

Z28KLR

Also, if you plan on flushing the system again, undo the drain plug on the block so some sh*t blows out of there. The bolt itself is about a 14 or 15mm head and is located near the freeze plugs between cylinder numbers 7 and 8. Kind of a bitch to get to on these cars, but not impossible at all.

weezel77

I agree that is a good question lol. Sometimes when stuff like this happens you over look the simplest things, i do in fact know the fan is coming on. I thought about testing it again actually and since you mentioned it I may do it first before messing with the leak down. When i tested it before it was soon after it basically puked it all out and had fresh coolant in it at the time. I didnt drive it hardly and it was just an idle state in my drive. Might sound dumb or lack of my knowledge but should i rev it up a little when block testing it?

Z28KLR

No, shouldn't need to rev. Drain some coolant out so the level sits a couple inches below the cap (basically to the top of the core section), allow the engine to idle with the cap off until the t-stat opens and you have full circulation, then at that point you can do the test.

EDIT... Oops, I was thinking about how I did it on my Exploder.... Shouldn't need to drain out any coolant since you will be inserting the block test thingy into the reservoir. Just make sure fluid level is low enough that none will be sucked up into the block tester, thus invalidating the test.

Z28KLR

If the test turn up positive results, then you can follow up with leakdown to determine which head needs to come off, unless you plan on saying f - it and doing both.