Coolant level slowly going down over a month or two

AKSION4YA

MEMBER
2005 TOYOTA TACOMA
4.0L
6 CYL
4WD
AUTOMATIC
130,000 MILES

I have topped off my coolant reserve container two times now. Each time after one to two months it will go from the "max" level down closer to the "low" level, again after close to two months. I had a very minimal amount of white stuff in oil filler cap, in last year have had none though. Also, no white smoke out exhaust and no sweet smelling exhaust. No leaks can be located on engine or on pavement also spark plugs looked normal. I have to add roughly three quarters to a regular glass amount of coolant about every two months. Truck does make an unusual noise (kind of a faint knocking sound on cold start up that can only be heard inside truck with doors closed/radio etc off, but then goes away after about a minute.

Hoping this is not a head gasket issue, if it is what would be a good price point to have it corrected (labor/parts) so I know I am not getting ripped off?

Any other causes I may be overlooking for such a slow coolant "disappearance"?

3 Replies

STEVE W.

MECHANIC
13,452 POSTS

Two most common invisible coolant leaks = Head gasket and heater core.
Two tests that you can do to determine which is the issue. One is a cooling system pressure test, it is basically applying 12-14 psi of pressure to the system and then watching to see if the pressure drops. Then you look for the leak. To make this test easier you can buy a UV dye that you add to the coolant. Then you look for the dye in the exhaust or in the AC drainage water or around the cooling system areas.

The other test looks for combustion gases in the coolant. Because the system is sealed there should be none. This test uses a fluid that changes color if those gases are present.
Both of these items are available as loaner tools at places like Advance and AutoZone type stores.

This shows some ways to test.
https://www.2carpros.com/articles/head-gasket-blown-test

this guide may help as well

https://www.2carpros.com/articles/car-is-leaking-coolant

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Tuesday, October 24th, 2017 AT 2:13 PM

STREAMWALKER

MEMBER
1 POST
2005 TOYOTA TACOMA
6 CYL
4WD
AUTOMATIC

'05 Toyota Tacoma; 4L, 6 cyl. 4WD. 63,000 miles; coolant changed at 45,000 miles. Thermometer placed in dash heater vent shows 140 degrees maximum in driving mode; at idle, temperature drops to 105 degrees within 3-4 minutes (outside air temperature approx. 30 degrees). This 35 degree swing from 140 to 105 is excessive according to mechanic. Note that during idle, temperature guage remains constant which lessens suspicion of thermostat. Coolant level has remained constant, no visual leaks, no unusual noises, no fluctuation in temperature guage. All of which lessens suspicion of water pump. Heater core was flushed, no blockage suspicions; coolant flow is good. Diagnostics indicate sensors are functioning properly. First, do you agree that a 35 degree swing is excessive? If so, what are your suspicions? Thanks for the input.

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Thursday, November 2nd, 2017 AT 9:50 AM (Merged)