Weird cooling system issue

If anyone could run any fresh ideas or has had similar issues? Any ideas this has got me stumped.
2004 v6 4wd 160k

Before it was only when idling my temp would climb like crazy then after letting it cool as long as I was letting the radiator catch airflow it would stay cool. Now it’s happening even while driving where out of no where my temp will start to rise. The radiator and condenser are both clean from debris/bugs. Been fighting this issue for a year now intermittently. No oil in radiator no water in oil pan. I have burped the radiator multiple times now using the funnel method while the heater runs. Letting it run for 30-45 minutes til no more bubbles are coming up. I’ve replaced the water pump once; the fan clutch, radiator cap, and thermostat all with OEM twice now. And I can’t track down figure this out. Is there hidden air in the system? Am I missing something. I’ve been trying to figure this out for a year now and it was never as bad or constant as it is now before it would happen every so often maybe once a couple months now it’s every other day that I’m not comfortable driving around even in town.

I don’t know if this is relevant but I do occasionally get AT temp light when I’m doing an incline that causes the auto to shift a lot. Usually what avoids that is staying in 2nd or 3rd depending the speed I need to go.

 

Does the fan work?

 

The fan does spin that’s why I was wondering if maybe I’m getting air from somewhere I can’t see and causing the fan to not get water behind it to be able to kick on? I have a spare clutch I’ll be swapping o it tomorrow but the one in there is the second oem in the span of a year I’ve replaced “just in case”

 

Try pressure testing the cooling system and see if you lose pressure after it sits a while

 

Pressure test. If thats good hope mechanic in a bottle was never used. Could be all the crap finally blocking the cooling passages.

 

Had a similar experience with my '86 pickup(22RE) , I recall trying everything, like you are. A friend said try and park it uphill, with the radiator cap elevated, take the cap off and let it idle at temp. , watch and see the air bubbles come out. I thought yeah right, but tried it, and after a while of watching bubbles in the radiator filler neck, they quit, put the cap back on, took it for a ride, no more temp gauge bouncing around. So yeah you might have air lock going on somewhere. It sounds dumb, but it worked for me. Good luck

 

thermostat?

 

Sound like you’ve replaced the key components except radiator, correct?

Have you ever used a cooling system stop leak product?
Ever use non-OEM coolant?
Are you losing coolant at all? Have you tested coolant for combustion gasses?

 

I have never used stopped leak leaks on any car I’m second owner but bought with very very low miles when it was still just about new. I’m waiting on adapter for my stand pressure tester for my radiator. Should be coming in tomorrow. I will be also trying an uphill burping as previously suggested. Will update tomorrow. Thanks!

 

Headgasket leak?

Also the AT temp switch trip point is quite high. By the time you get the light, the fluid is already cooked and some transmission damage may have already occurred.

 

OP, have you confirmed the coolant temp sensor or associated wiring is giving good info?

typically when they fail, they’ll fail to zero, but it you gat an intermittent high resistance (poor connection/corrosion) it could register as higher than actual temp.

aside from that, or a partially clogged radiator you’re probably looking at a head gasket leak.

 

I actually haven’t even thought of it might just be the temp sensor but I’ll check that out too if the pressure test later today doesn’t show anything. Thanks!

 

W/ head gasket wouldn’t I be finding water in oil pan when I took that off or oil in coolant when I drained it? Because I found neither. but I always thought that’s how you could tell. Please do correct me if I’m wrong though as I’m still stumped.

 

Okay so update ran pressure test. On both my new cap and that was good and then on the radiator/system and held pressure for an hour and at around 3.5 hours since I left it at lunch to come back to after work it had started dropping slowly but that was after a few hours and could be from the tool? Will be doing a hill burping next.

 

You don’t always get coolant into oil. Head gaskets can fail a number of ways, coolant to the cylinder or oil passage are two failure modes. They can also leak combustion gases to the cooling system, which displaces coolant resulting in hotspots and overheating. Presence of hydrocarbons in coolant is evidence of head gasket failure. Hopefully that is not the case.


Re-reading the original post… at you only overheating at idle? If that’s the case, I’d probably be looking at a blocked radiator. Also, use a
Scan tool with live data to watch coolant temps. If you see rapid changes in temp, or implausible values, it probably the temp sensor.

 

yes only at idle. No visible blocks but maybe taking a light pressure washer to wash it out just in case. I will be investing in live scan so I can actually watch my temp. All I have currently is a cheap obd2 tool for codes.

 

That’s a good sign that you’re probably not dealing with a head gasket.

Don’t use a pressure washer on the radiator, it will easily damage the fins, potentially making your problem worse.

When the water pump, or thermostat were replaced, did you see any indication of sludge or scale in the coolant passages?

The internal passages in the radiator are very small and can easily be blocked… this is why I asked about the stop leak and coolant. Coolant incompatibility is a real thing, and the wrong coolant added by a previous owner can create sludge that can block coolant passages.

 

No, because the head gasket area doesn't see oil. Effectively all the head gasket does is to separate the coolant from the combustion chamber. Leaks occur due to the coolant eating away at the gasket material. The overheating could be caused by the combustion gases getting into the cooling jacket.

 

Update: okay so did a pressure test on both my system and the cap. Both were good. System held pressure for an hour. Replaced my fan clutch and the problem seemed to go away for about a week. Driving was normal and fine and that’s with my AC going almost 24/7. Then last night it just started happening again. I’ll try the hill burp as someone else suggested. I did test my temp sensor and it’s working.
One thing that still confuses me is this is only an issue when I idle for anything longer than a moment. Like at a stop light I’m good. But in bumper to bumper traffic. Or at a drive thru it’s climbing.

One other thing to note is my fan clutch before I wouldn’t hear it engage when it was warming up. And this new one I don’t hear it engage either when it gets hot? I don’t know if maybe I got some really bad air in the system not allowing it to heat to engage?

edit: just thought maybe the water pump isn’t transferring the heat? Because the old fan clutch wouldn’t engage and now this new one won’t either? Both were OEM and had good resistance when cold.

 

It looks like I’ll be picking up a combustion leak detector as well then to see if this is the cause of my issue I feel I’ve exhausted almost everything else.

 

With the engine idling, open the radiator cap and see if you get a lot of air bubbling out. Do this when the coolant is cold, like on a cold start first thing in the morning.

 

So it looks like it has a combustion leak

 

^Time for a lower-mileage used engine. Tacomas had this engine up until 10 years ago (2015), though I think you'd need to block off the exhaust manifold air injection ports.