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HELP ! Losing coolant, but no leaks?

Hey Guys, its been a long time. I am currently driving a 98 Buick with the 3.8 V6 and 120,000 on the clock. The car runs 100%, and its paid for :slight_smile:

My problem is I seem to be losing coolant, at the rate of about the entire overflow in 2 weeks (I only drive on avg 15-20 miles a day). The problem is I have no leaks. I even went so far as to pull the spark plugs and they all looked good (none of them looked “steam cleaned”). I put florescent dye into the rad, and I can’t find a drop of coolant anywhere. The intake gaskets have already been done on this car, and I triple checked around it with the die.

Rad, and hoses all check out, no dye in the oil, no dye at the heater core/AC drain under the car, the core plugs are fine, around the head gaskets seem fine as well… I CANT FIGURE THIS OUT !! I am 100% losing coolant, but I can’t find hide nor hair of it… ANY suggestions would be appreciated !!

I know I can keep adding coolant, but I like my cars as leak free as possible and if it is something bad, I want to know about it now not later.

Thank you in advance

The first thought that comes to mind is that the coolant is getting pushed out the reservoir overflow tube when the engine warms up because of a bad radiator cap. A pressure test won’t show this, because one has to remove the radiator cap to do the test! You can test a radiattor cap with a thermometer, a hotplate, and a Pyrex vessel. Simply hang the cap into the water, turn the hotplate on, and see what temperature the T-stat opens at.

Hey Mountain good to see you are still around. I forgot to mention the pressure test, when pumped up to 15 PSI it feel to around 10 or 11 PSI after about 10 or 15 min. I was told it is possible I did not have a good seal at the radiator. The overflow line (from the rad to the overflow container) was pinched off at the time of the test.

Still though if I am losing coolant with die in it would I not see it somewhere around the over flow if this was happening??

Did you use the UV sensitive dye?

There are other possibilities.
Unless I miss my guess, that era used a radiator and a tranny cooler both in the same package, and if there’s a breech between the two portions than coolant under 15PSI could get pushed through the breech and into the tranny cooler. How’s your tranny fluid been?
Also, have you been smelling any sweet smell when the heater is on? You could have a miniscule leak in the heater core. You could if you desire pressure test this loop seperately from the rest of teh cooling system. It’s a simple matter of disconnecting the heater hoses and testing there. You’d have to jury-rig a hookup, but that’s pretty simple.

Yes UV sensitive dye (I work at a Honda dealership and they have all of the UV lights and eqipment)… I did check the oil and trans fluid for signs of the dye and came up empty on both counts. No smell of antifreeze, no white smoke while running, dry floors, no dye under the car at all (looked all around the pass compartment as well)…

Keep the ideas coming !!

I’d still pressure check the heater loop seperately.

But I admit that I’m stumped. If I think of anything else I’ll post.

It is a slow leaks about an overflow in 2 weeks and no dye marks.
The leak may be happening from the bottom hose or radiator drain. It may be happening only when the car is hot when you drive and the coolant is under pressure. Try checking it when it is hot, under pressure and while the engine is running.

The coolant pressure test is obviously showing a coolant leak. The system should not lose pressure if there were no leaks. Since the leak is not external, it may be getting burned. Maybe the intake gaskets leaking again?

Did you check the exhaust for any traces of UV? Another thought is to repeat the pressure test, pull the EFI or ECU fuse to de-power the fuel injectors, and coil, and, after 10-15 minutes into the pressure test when the pressure drops, turn the engine over a few times. Then pull plugs and check for traces of UV dye on the spark plugs. If the leak is slow enough, it may be getting burned before it can drop into the crankcase.

Do you have a check engine light on or any misfire codes stored? Notice any rough idle or misfire momentarily on cold start-up?

You have a plastic upper intake, correct? These are problematic in that directly behind the throttle body there are 2 small coolant passages adjacent to the EGR inlet to the intake. Hot exhaust eventually cracks the plastic to the point that a small amount of coolant can enter the inside of the intake. Not enough to cause any problems at first, but as it progresses, well, I’ve seen them hydrolock.

Sounds like you’ve looked at all the common problems. Maybe it’s time to pull the plenum.

It’s possible to have a pressure loss between the pressure tester and radiator. I’ve seen this more than a few times. You might consider wiping the connection surfaces down with a cold, heavy grease as this can help stop any pressure loss. Stick the grease in the fridge for a few hours if need be. (Yes, this can cause disgruntlement with a better half.) :slight_smile:

What about the pressure cap? These can be a hit and miss thing sometimes and maybe coolant is being lost on an erratic basis while the car is at speed on the open road.

We had a Subaru in once with a coolant loss complaint in which everything checked out fine; multiple times.
Come to find out there was a narrow window (between 7 and 8 minutes) in which the pressure cap would allow the radiator ot puke anti-freeze for about 20 seconds or so.
It would not do it at the 5 or 6 minute mark or when in excess of 8 minutes. A new cap solved that.

Glad to see you’re still around GS. It’s been a few years.

Thanks guys for all of the ideas, I have a bad feeling that ASEmaster hit the nail on the head. I have had a misfire at start up 3 times in the last month (always cyl #6 which is closest to the EGR valve). I assumed I had a bad plug wire (even though they were only about 4 years old and 30,000 miles) as it always seemed to happen on humid mornings, and would go away after about 30 seconds of running… I did a full tune up on it last weekend and have not had a misfire since, no codes no nothing. Also a bad intake would explain the lack of leaks, and complete lack of evidence of a bad head gasket…

Let me ask you this, can I assume that if I remove the air intake, and open the butterfly on the throttle and shine the UV light in I should see the dye in the intake right??

I am leaning away from the rad cap only because I am not getting any dye around the rad cap at all, and even if it was venting coolant every now and again I should see dye residue around it.

Thanks again guys

OK answered my own question on shinning the light thrugh the throttle body, there is a mettle mesh screen right at the front of the body, I cant see thrugh it… Besides removeing the throtle body, any other ideas how I can see what is going on inside the intake? I just want to shine the UV light in there and see if I see the yellow dye.


The mesh shouldn’t cover the entire inlet below the TB. You may be able to see something with a borescope.

When I pull the air intake elbow off the TB, the mesh screen is right there, and it does cover the entire inlet. I wonder if I can remove it with out damageing it… One of the techs has a borescope, but I would not be able to get it past the mesh.

Your’e going to have to warm the engine to operating temperature, remove the throttle body and pressurize the cooling system to inspect and see if this is in fact the trouble you’re having. Here’s a link I found Googling 3.8 plastic intake egr:

ASE, thanks I found that blog yesterday… It was very helpful… As a follow up I just got a new intake, the local AdvanceAuto matched’s webprice of $78.00 so it should be a cheap fix… Lets just hope this is the fix, i know my fingers are crossed :slight_smile:

I will tell you this much they as well as some other local autoparts stores had this in stock, which just goes to show you that they must fail all of the time, because I know these guys don’t carry things that dont sell at the store level.

Actually the frequency of this repair seems to be declining in recent years–at least for me, I think a lot of them have been replaced already. Did you get the kit complete wih PCV valve? Make sure the PCV o-ring is in place. And don’t break the MAP sensor switching it from one intake to the other. :slight_smile:

To: The same mountainbike,
I don’t understand putting a pressure cap in water and heating it. It opens by pressure , not temp.

Boiling water creates steam pressure…

hi all, I’m also in need of some help with a coolant issue.
I have a Peugeot 307 1.6 hdi sport 2006
I’m losing coolant at a rate of a full resovour every 3hours,
All the usual checks have been carried out, the head gasket is fine, no coolant in the oil or oil in the coolant, nothing in the exhaust vapour, no visible leaks of any kind within the engine bay. The car has recently had a new EGR cooler and coolant tank sensor.
I’m at a complete loss here please help