Coolant Puddle


Veteran Poster
Sep 22, 2023
Richmond, VA
Country flag
Just as I was worrying about 1st world problems like inadequate lumbar support and not quite quiet sway bar bushings, I run into what I fear may be a  real problem.

I saw this puddle today for the first time, though that area always looked moist to me. Passenger side pictured; driver side condition unknown.

To give some context, during close to two years of ownership, I've observed a very slow coolant leak, requiring top-off every six months or so, and that's top-off before the low coolant light even comes on.

I'll monitor for the time being. I'm not prepared for a major (gasket) repair at the moment...

The only way for coolant to get on TOP of the manifold like that, is from one of the hose connections or sensor / vent plug fittings.
Can you get a coolant pressure tester from autozone on loan? Or buy one at Harbor Freight? fill the system and pressure test it. You'll find the leak quickly.
Based on where the puddle is, I suspect it is the coolant line going through the throttle body. Probably a quick and easy fix.

But that seems to be made from metal (?). I'll have to look again. I couldn't see any leaks earlier. I just assumed it came from below through some gasket...
The intake only has coolant going through at the very front and very back, and if the gasket blows, it usually leaks down the block or into the valley, not up on top of the intake. Also the thermostat on the 3.8 is vertical on the front of the manifold, so that would leak down the front of the engine, not up onto the intake. The coolant hose going through the throttle body is right in that area, or it could be a heater hose with a small leak, but I highly doubt intake gaskets, and definitely not head gaskets.
I'm afraid it's impossible to see where it comes from without removing at least the throttle body. How difficult is that?

Meanwhile, I went for a short 10-mile drive. The puddle disappeared.

I'm guessing the leak is further back. The entire area aft of the puddle is moist, but not forward of the puddle.

Forgive my ignorance: what is this extremely corroded part, and why is it so corroded?

The corroded part is the EGR valve. It's rusty because it gets hot and is made of cast iron.
Pressure test the system. You can do that without removing the throttle body.
All of my 4.6's are known to boil after I park them, after a drive. They boil, open the cap, and after the pressure comes off Really boil over. I've changed my driving to ensure the operating temp is lower before I park. :) The trans temp has a lot to do with this too.
Other priorities (crankshaft sensor crap) keep me from this; however, that small puddle is still alive and well, and I cannot see any leaky plumbing.

At this point, I'm pretty sure it's the lower intake manifold gasket. I've been reading up on the repair, and it's on my to-do list. I also found this article on the subject:

Meanwhile, I have excellent lumbar support; so it's not all bad these days.
Just my two cents, but I would rent the coolant pressure test kit from the parts store. Take off the intake tube and the cover over the throttle body, clean all of the coolant that has puddled, pressurize the system and look for leaks. It isn't a terrible job to remove the lower intake, but I wouldn't do it unless I was sure that was where the leak was coming from.
The coolant pressure tester is your friend. It's a simple and easy test. And it is very effective for finding that type of problem in most all cases.
I'm with MadMikey on this one. Test it before you shotgun a repair at it.
With the coolant pressure test it's not like you have to be a highly trained tech to weed out some difficult electrical problem. 9 times out of 10 the coolant leak will present itself like you turned on a water fountain to take a drink.
So nobody can say I didn't listen to good advice:


Unfortunately, the result isn't encouraging. I pressurized to 16 psi, which is the pressure indicated on the cap.

No audible dripping or hissing; however, the area on top of the lower intake manifold, which was dry prior to the test filled up. It just seeps out of there.


In normal use, the loss of coolant is very slow, and there are absolutely no signs of coolant in the oil. So it doesn't need to be fixed  today. But iit'll have to be done...
Well that would be intake manifold gaskets. The injectors on the 3.8 go into the cylinder head, so that spot is where the lower intake meets the head.

That's my thought unless a second test leads to different results. I just need a few days to regain my

It's really no disaster. It's perfectly fixable. And frankly, I'd be way more upset if it leaked into the oil, which it doesn't.
Check the head and intake surfaces, I had severe pitting after only 3 years on the coolant. If you don't clean out the pits and fill them, it leaks under the new gasket. :( I had to pick it out and backfill with rtv. rust sux, even if it's aluminum rust, lol.
If you get a friend over to pump the tester while you watch then it will help find the leak. Of course dry everything first. But it does look like the gasket is leaking at the coolant crossover. Not a horrible job, but just takes time.
If you get a friend over to pump the tester while you watch then it will help find the leak. Of course dry everything first. But it does look like the gasket is leaking at the coolant crossover. Not a horrible job, but just takes time.

Drying it isn't even necessary. Just driving a bit dries everything up. The puddle only forms after driving, and never as large as during this test.

In actual operation, it takes months until I actually have to top of the bottle. Of course, likely that'll become worse as the leak grows.

What bothers me a bit is a big-ish puddle that formed on the ground during the test. Coolant was dripping down at the back of the engine.
That was either this leak, assuming the engine is angled slightly downward toward the back; or there's another leak back there which I couldn't see.

Similar threads