There is a UV dye you can add to your coolant. Run it a bit until you feel confident it has fully circulated and then break out a UV light. Find where it is glowing and keep going until you find the highest glowing point and your leak should be there.

 

Tracing a leak with a dye and an ultraviolet light is very effective. If you still have a problem finding the source of the leak, use a cooling system pressure tester. You might also look closely around any hose connections around the engine. A crusty deposit at a hose nipple is a prime point to investigate.
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Mine had a pinhole leak at the top of the rad that left a small stain down the side of the rad.... my buddy had exactly the same leak... so slow I only noticed it by the dropping reservoir level.

Of course, any part of the system can leak...

 

Apparently I had a small leak on some kind of plastic part near the thermostat. I will be picking up the car and talking to the mechanic next Monday, I'll get the name of the part and post it then.
-Chris

 

Sorry for the delay. He said the part had different names depending on the supplier, but it was basically the plastic part with the thermostat housing. He said it was a tiny leak along the seam when the part was formed.
-Chris

 

Thank you for all the replies. I will try the UV dye method. I have used it with great success to find A/C leaks but never tried it for coolant leaks.

Chris - I will be interested to see the solution to your problem as my drip is located below the thermostat housing but I can't gunpoint the exact source.

 

If it's a hard part and not a hose, you might put a half-tablet of Bar's Leaks in your coolant. Do it at the radiator neck where the cap is. I've had good luck with this in the past. Don't use more than you need since it can abrade the water pump impeller over time.
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Problem appears to be solved. I tried the UV dye method but couldn't locate the source of the leak. Because the only coolant related part that was above where I saw the drip was the plastic part that houses the thermostat and also all the hoses connect to, I assumed that this might be the source of the leak (Thanks Chris for pointing me in the right direction). The manual refers to this piece as the"Water temperature control assembly". Parts suppliers call it the "Water crossover". It goes between the two heads and houses the thermostat. Both radiator hoses connect to is as do the heater hoses and throttle body coolant hoses. To remove the assembly, I removed the battery, battery tray, the whole air cleaner assembly. I also had to disconnect all the hoses, a sensor and unbolt the engine harness. The assembly is attached to EACH head with two nuts and one bolt which require a 12mm socket. Once you have removed all four nuts and two bolts, you can wiggle the assembly off. I thoroughly cleaned all mating surfaces and replaced the two formed rubber gaskets that go between the assembly and each head and an O-ring that is at the center of the assembly and connects the assembly to a "mystery" pipe. Put it all back together and no more leak!

This was not a fun job. The Hyundai service manual was of little help.

 

I'm sorry to report that the problem was not solved. The leak is back. It only seems to leak when it is stone cold.

Plan B is to remove the battery and battery tray so that I can see into the area, then pressurize the system when the SF is cold. Maybe then I can actually see the source of the leak rather than just guessing.

 

I had the same problem. The coolant expansion tank would be low every 3-4 weeks. I never saw a leak evident, or drops on the pavement, but one morning I did see a drop of coolant on the bottom of the engine.

I had to take it to the dealer twice. The first time they replaced the T-stat housing under warranty. It did not fix the issue. Additionally the CEL began to come on intermitently so I took it back.

Like your experience, it is only evident when it sits cold overnight. It was so slow that when warm it evaporated.

The second time the dealer asked me to bring it the night before, gave me a loaner Sonata, and they looked in the AM and saw the a drop of coolant on the bottom of the bell housing. They then did the dye test and found the synthetic intake manifold was cracked. It was fixed under warranty and has not returned. BOth the leak and the CEL were from the manifold issue.

Fortunately it was all under the Hyundai US warranty.

 

Thanks Bill for your reply. I certainly hope that my manifold is not cracked. I would guess that it would quite an expensive part and my SF is out of warranty. I changed the spark plugs a while ago which requires removal of the upper intake manifold. I don't recall any coolant passages in the part that I removed.

I just received the adapter for the radiator that will allow me to pressurizer the cooling system but have avoided going out and working on the problem because its been really cold outside here in Michigan.

 

I think I have the leak solved this time. The hose that goes between the heater and the "Water temperature control assembly" was leaking at the "Water temperature control assembly" end. I probably could have just put a different clamp on it but elected to go with a new replacement OEM hose. So far no coolant loss. I'm keeping my fingers crossed.

 

I replaced the hose with a new one and coolant loss was reduced but still had some loss. I borrowed a boroscope from a friend and a pump with adapter that would allow me to pressurize the radiator when the engine was cold. With the system pressurized and using the boroscope.I could see a tiny leak on the underside of the plastic pipe that connects the two head, houses the thermostat and the parts book calls a "Water temperature control assembly". This, I believe, was the part that Chris was referring to in a previous post. The leak was at a mold seem. With the part off, you could barely see the crack. When I had this off before to replace the gaskets, I looked it over carefully and never saw the crack.



I replaced the part and have had no further coolant loss now for over a month. Interesting that this part is available from aftermarket suppliers. This would suggest to me that it is a part prone to failure to justify manufacturing it. Also, I looked at my friend's 2007 Santa Fe with the same engine and the piece is made of aluminum. I guess Hyundai decided to save a few pennies or a couple of ounces.

 

astr - I'm glad you found the leak and fixed it! I'll keep this in mind if my 2010 develops a similar leak.

One item of note - your friends 2007 Santa Fe has the older 3.3L engine and not the 3.5L engine that yours has. I guess when Hyundai designed the new engine they cut a few corners on cost.

Cheers!

 

a...One item of note - your friends 2007 Santa Fe has the older 3.3L engine and not the 3.5L engine that yours has. I guess when Hyundai designed the new engine they cut a few corners on cost.

Cheers!

I went back and checked with my friend. His SF is a 2005, not 2007, and the badge on the back says 3.5l. Was there an earlier 3.5L?

 

i have a slow leak on my 2010 v6 as well and i will need to try and diagnose.

 

Put it under pressure and look. May need to remove air intake to see. Dye is not the easiest way to go. Pressurize the system.

 

It is fixed. See Post #15. And yes, I had to pressurize the system while the engine was cold to find the leak. It wouldn't leak when hot. I did have to remove the air intake, battery and battery tray to see the leak.

 

Is this the thermostat housing?

 

It is the plastic pipe assembly that runs between the two heads and all the hoses connect to it. It also houses the thermostat. Rock Auto refers to it as the Thermostat housing/Water outlet. Hyundai call it a Water Temperature Control Assembly. I call it an expensive engineering mistake.