Disappearing coolant

No visible leak. Negative block test/dealership (and myself)/coolant resovoir. PSI/ 15psi held 10 minutes/dealership/pressure test. Changed oil in Dec, normal. Drained 1 cup from oil pan today- normal in color. Coolant still disappearing. Full resovoir 12/17, now at 1/3 full. No coolant loss in the past.

 

Was the engine warm? Sounds familiar. I never saw any water in my oil either. But the oil level did rise but only on the morning of head gasket failure. What year Taco is this?

 

I had a similar issue but mine was because the radiator cap failed and it was escaping from the reservoir.

 

may need more than 15 PSI..

 

A 10 minute pressure test isn't long enough, IMO. Several hours at least with a good tester, overnight if possible. Depending on temperature swings overnight, anything more than 2 psi down is a red flag to me.

I had a 2.7L go T/U with a bad HG. Primary symptom was a rough start along with sweet smelling exhaust at startup. It otherwise ran fine with no overheating or boilovers. The leak into cylinder 3 would happen overnight, and that's how I confirmed - with an overnight test on a pressurized system.

 

Headgaskets are odd on Toyotas, they will only leak under certain scenarios.

You need to pressure it and watch each cylinder with a boresecope. It won't show combustion on a tester.

Another method I use is coolant funnels. If there's tiny bubbles its almost always a HG.

https://www.youtube.com/shorts/_oWXDmrs96c (my video of the bubbles)

 

Get a coolant funnel amd put on radiator. See if it bubbles. My coolant never made it to the oil but was sucking air in from exhaust side. Probably being burnt off. With exhaust.

 

I have a different engine (4.0L) and had the same "disappearing coolant" issue. I could not see any visible leaks anywhere. I also did a block test and it passed. I did pressurize my radiator and did not notice any obvious drop in pressure. It was only until I inspected the cylinders with a borescope that I found out that I had a head gasket leak. Even if I left the radiator pressurized over night and it did drop a few psi, I don't believe I would still feel confident in assuming the head gasket was bad unless I had visible confirmation of coolant leaking into the engine.

 

Thanks!

One online video showed using boroscope while pressurizing the radiator, and could seek a tiny drip into the cylinder, but dealership, won't usu boroscope unless fails radiator pressure test.

I drained ~1/3 cup oil from oil pan yesterday, oil looked normal, but thinking of trying the boil test. Place 1/2 teaspoon of oil on a heated pan or foil and if bubbles, there is water/coolant in the oil.

 

It burns it doesn’t mix with the oil.

 

Will look online to see how coolant can burn off on the exhaust side and not contaminate the oil. With these aluminum engines, is it worth the trouble replacing the head gasket?

 

Will use the coolant funnel too to see if bubbles like in the video provided.

 

Yes it's worth it to replace the head gasket.

What's your mileage? Did you check the water pump as well?

 

I assume it is similar in concept to the open deck design of the 4.0L V6. See below.

 

114, 000 miles 2006. 2.7 L 4 cinder regular cab.

 

No leaking from water pump. Temperature almost at halfway. I think use to run just a little cooler. No overheating.

 

What about pink crusty residue around the weep hole on the WP?

 

No, but will use a flashlight and look again. No, not seeing any crust at all on the water pump.

I was getting pink crust at both ends of the hose that connects radiator to the coolant resovoir, and replaced the hose and radiator cap, in November. Now I'm seeing a white crusty streak down the fan cover below the coolant resovoir, but dealership said its nothing. How could it be nothing. I wonder if the coolant resovoir might have a small crack somewhere.

 

I pressurize each cylinder with a leak down tester...put a funnel in the radiator...if leaking coolant will bubble or rise

 

Another thing to check is below the thermostat housing on the driver side of the block. See if your truck has the plastic coolant bypass pipe no. 1. Maybe that's slowly leaking? more info here
https://www.tacomaworld.com/threads/water-bypass-pipe-no-1.201053/

If your coolant is being pushed out of your radiator and into the overflow reservoir, its typically either a bad radiator cap, or a bad head gasket. Mine would fill the reservoir more when driving on the hwy. After pulling off and leaving it running, you could see bubbles in the overflow reservoir