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Mysterious coolant leak

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Jan 9, 2021, 7:33 PM

Post #1 of 2 (457 views)
Mysterious coolant leak Sign In

Mysterious coolant leak? on 2004 tundra 4.7 v8

I’ve been having this issue for about a week now, and I’m starting to get stumped
Hoping anyone here has any insight on direction I should take, any help is appreciated.

So about a week ago I was driving and I noticed my temperature gauge spiking up to full and almost instantly dropping back down to normal, did that a couple times inconsistently before I was able to pull over and check things out, noticed my coolant was low topped it off with water, everything went back to normal and I assumed it was a leak.
After looking all over for a leak I couldn’t find anything externally. I checked my oil cap and noticed white milky sludge in the cap, instantly thought it was a head gasket so I got a block test to check for combustion gases in the radiator it passed that test. I looked further down the oil fill and noticed the oil in the engine is clean and so was the oil on the dipstick, assumed it was just from short drives in a humid area (pacific north west). So I took it into a shop and had them do a pressure test and lift it up to see if they could find any external leaks. They said it held pressure and couldn’t find any leaks externally and that it must have just been an air bubble or a bad radiator cap so I replaced the cap, topped off the coolant and a few days later I was low again. I decided to get some UV dye to put in the coolant and my own pressure test kit, when when I did the pressure test I pumped it to 16 psi and over the course of 10 minutes it dropped to 14. No visible leaks anywhere.
My next order of business is to pull all the plugs, pressurize it and check the cylinders for coolant.
Other notes: white smoke/steam from tail pipe is only during startup and once it gets to operating temp, goes away.

My questions for you guys is

-what are all the ways coolant can enter combustion chamber ?

-if coolant is getting into the combustion chamber will there always be sign of exhaust gases in radiator?

-how long should radiator pressure test hold pressure and at what psi?

-if it was a head gasket or something with the block would it be driving/idling/and operating normally for the last week?

-anything else you think I should check before I start taking things apart ?

Tom Greenleaf
Ultimate Carjunky / Moderator
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Jan 9, 2021, 7:52 PM

Post #2 of 2 (447 views)
Re: Mysterious coolant leak Sign In

S lot to read I do too much of that too. Oil milky under oil fill cap?
Yes it's NW US is wet, humid and cold at night engine block condenses moisture. May be normal for this time of year and back some.

* No evidence in oil of combustion leaking into cooling system? There may not be and it doesn't always do that. Add to that the sniffer tests of coolant IDK if I trust those.

So, hidden coolant leak with spiking temp gauge - hmmmm? Maybe fan(s) don't kick on or real late? Just this part begs the question how much coolant are you needing to add? Bet none yet.

* Smoke out exhaust only while cold. Normal you knew that didn't you? Fuel makes warm water vapor you see it when cool or cold it does go away.

Back to spiking gauge: That is the warning need to see fan work it's late IMO. Sometimes asking for defrost will force many on if that works next is either air in system making sensors late or switch to trigger fan is faulty and late.

If no coolant loss pressure testing is also expanding hoses so reading can drop but just once then stay there so alone that's not conclusive of anything by itself,


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