Coolant leak either at or above thermostat

[358R]

Vehicle: 99 Mounty 5.0 rwd

So, here's what I know...i can see streaks of where coolant has been leaking from what appears to be the hose that feeds into the thermostat. I've tightened it down a few times, but still seem to have the leak and it's puddling up right below. I've filled up the overflow reservoir several times (while cold) and it always seems to drink it up (ie the overflow is always empty). But, on the other hand, i've never seen my engine temp spike or anything...and when i take the cap off the radiator, it's never low. What am I missing? I did search the forum with a few different searches...and i see bad intake manifold gasket or bad thermostat gasket/housing. Thoughts?

 

[Junkmann2]

I had the same problem with my '97. It turned out to be a cracked plastic thermostat housing. I didn't bother to fix it because the rust worms had attacked the frame to the point that the rear bumper was about to fall off.

 

[redexplorer5.0]

have the same problem once before it was coming from the thermostat housing im having the same problem again going to replace the housing,thermostat and the hoses again

 

[1998Exp]

My standard answer to questions like yours is to rent a pressure tester and find where it's actually coming from, instead of guessing. Be aware that the 5.0 is notorious for failure of the gasket under the timing cover in the top right or left corner. If you don't see anything leaking out of the thermostat area and coolant is puddling behind the timing cover, that's the most likely culprit.

Vehicle: 99 Mounty 5.0 rwd
So, here's what I know...i can see streaks of where coolant has been leaking from what appears to be the hose that feeds into the thermostat. I've tightened it down a few times, but still seem to have the leak and it's puddling up right below. I've filled up the overflow reservoir several times (while cold) and it always seems to drink it up (ie the overflow is always empty). But, on the other hand, i've never seen my engine temp spike or anything...and when i take the cap off the radiator, it's never low. What am I missing? I did search the forum with a few different searches...and i see bad intake manifold gasket or bad thermostat gasket/housing. Thoughts?

 

[bobflood]

My standard answer to questions like yours is to rent a pressure tester and find where it's actually coming from, instead of guessing. Be aware that the 5.0 is notorious for failure of the gasket under the timing cover in the top right or left corner. If you don't see anything leaking out of the thermostat area and coolant is puddling behind the timing cover, that's the most likely culprit.

+! on both thoughts here - the pressure tester and the timing cover leaks. Good luck.

 

[beach]

When was the last time you change the t-stat and gasket? Its a common leak from that area, the housing just gets pitted over years. Mine has a very very slight drip that just barely puddles under the housing, I just changed my t-stat and used a gasket and water pump sealer as well.

If yours is leaking that bad to where your filling the reservoir up, could be a number of things as mentioned. Gasket failing, the hose it self can actually develop cracks that can leak that are hard to see etc.

See if you can dry/clean the coolant up. And let the truck run and watch and see if you can tell where the leak is coming from. Can pressure test as well like mentioned.

 

[358R]

Thanks everybody. I'll look into all the above mentioned and report back for documentation's sake.

 

[358R]

So, I had a minute to work on it yesterday. Started the truck and watched it run for about 5 minutes (water temp needle didn't even move). I noticed fairly quickly that it was coming from around the radiator hose. Bought a new one last night. Will attempt to fix today and report back.

 

[358R]

So, I replaced the hose and cranked it down. Drove around for a full day and it was fine. Then, this morning, I drove down the street (maybe 2 miles) and by the time i stopped and checked, it was already leaking again.

What am I missing? Maybe move the clamp up a little higher?

 

[358R]

Also, it may be just anecdotal evidence, but it seems that when I run with the heat on, it doesn't leak.

 

[bobflood]

Did you clean off the metal hose nipple before installing the new hose? I usually use steel wool to make sure nothing remains of the old hose. Centering the clamp on the smooth steel section might also help. Good luck.