Coolant Problem on 2.7L Tacoma

Hello everyone,

I have a 2005 Toyota Tacoma 2.7L with 290,000 miles and experiencing a coolant system issue. I have to add coolant to my truck about once a week. I noticed that even when I let the truck run for a long time with the heater on and the radiator cap off I still see bubbles coming from the radiator fill port. The bubbles never go away even after driving a small bit and topping the coolant off. I do not ever see any coolant on the ground after the truck sits for a while. I've done various troubleshooting tests and am still stumped on what the source of the issue is.

First, I used a combustion leak tester which came up negative, i.e. the color of the test liquid stayed blue. I made sure that the truck was at operating temperature before using the combustion leak tester. Next, I then used a cooling system pressure tester and put 1.1atm or 16 psi of pressure on the coolant system. I did not see the pressure drop after a couple minutes and did not see or hear any issues with coolant leaking from the radiator, hoses, water pump, or coolant bypass pipe. Note, the coolant bypass pipe was replaced by my dad with the new metal version maybe 8 years ago. I don't see any seepage by the water pump or the weep hole as well.

When I go on a drive and then check the coolant level I can hear and see the coolant go into the expansion tank. The problem is that the coolant from the expansion tank doesn't go back into the radiator or at least that's part of the problem. I just checked the expansion tank after a drive and see that it's a little overfilled and thus the coolant didn't go back into the radiator.

Maybe there is an issue with the exhaust side or something because there's always a small amount of white smoke when I first open the radiator cap after a drive. If I go on for a long drive around an hour or more the truck will overheat and then I'll see that the radiator and expansion tank is low. It seems that there is something wrong with the coolant somewhere when it passes through the engine block. Does anyone have any ideas? This is such an odd issue. Thanks!

-Matt

 

Do the bubbles increase with speed when you give raise the revs?

 

This. If the answer is yes.... I would say head gasket.

 

Hi Tirsod,

Yes, it seems that the bubbles do increase when I raise the revs. Here is a video I shot today.
https://www.youtube.com/embed/6S-Z-iOJk0w

 

I had very similar symptoms, including overheating, and my truck would do this after driving for awhile:

https://www.youtube.com/watch?v=qg4BuFaHqWc

Turned out to be a failed radiator cap. It actually disintegrated and fell into the radiator, I didn't notice for awhile that the guts were gone. $15 and I was back on the road. 75,000 miles since then.

I now keep a spare radiator cap in the truck. Such a cheap part but it can leave you on the side of the road.

 

Any issues after yours ate bottom portion of the radiator cap? Mine just did this yesterday

 

No. Well, not after fixing it I mean. Within a week I yanked the radiator, turned it upside down, and out fell the cap spring and a few other cap pieces.

There was a hodgepodge of different coolants in there from the overheating incident so I did a full drain and flush anyway, so the radiator wasn't much extra work.

 

Also this just looks like normal behavior as the water pump ramps up when you rev. I see the flow increasing but I don't think I notice a difference in the bubbles. It also looks like pure water to me, which since you have the cap off is going to be boiling at 212F (could this explain the bubbles?). Proper coolant under a proper 15 PSI boils at like 260F or something. I'm not sure about the bubbles though or why they're there.

 

In most cases, they are a direct indication of a head gasket problem.

 

I would agree, but he already tested for exhaust gasses in the coolant, which was a negative. Coolant not returning to the radiator from the reservoir is the tell for a bad radiator cap. The water boiling at low pressure, and pushing past the bad cap caused the bubbles.

 

But looking at his video that was posted the coolant isn't even steaming, heck it doesn't even look hot. Look at Andrew's video in post # 5 and it has a lot of steam in the overflow bottle.

I would change the cap just for giggles I suppose as it is cheap, but....

 

I would in most cases agree with my statement as well. Lol

 

This is more directed towards the OP than you. I just watched both videos. Hadn't at the time of my response. Jimmyh, stated it clearly. Plus, the 1st video, although somewhat helpful, is with the rad cap off. Cannot build pressure. Can't raise the temperature enough. Were it a pinhole headgasket leak, it would be much harder to tell, testing without the radiator cap on.

Seen a few older Tacomas, simply age alone, where the radiator cap has failed, such as @andrew61987 had mentioned. Cap had residue around it. As well as splashed elsewhere. Immediate thoughts were head gaskets.

We can all agree that start with cheap first.

A good radiator cap, compared to one that is 15 years old, will let us and OP know, if there are bubbles in the overflow. Only after the system has been bled.

 

I'm with the radiator cap first, then head gasket crowd.

If the radiator cap doesn't do it, a compression test is next I think.

On the one head gasket issue I had on a 4cyl the spark plug and piston top had been 'steam cleaned'. Easy thing to look at with one of those cameras that attach to your phone.

 

If the headgasket was leaking, wouldn't one of they cylinders be squeaky clean?
pull the plugs and see if any of them are really clean.

best of all, its free!

 

Hey guys, thanks for all your responses. I should mention that this issue has been occurring ever since I replaced a failed thermostat. Well at least that's what my dad and I thought was the problem. After replacing the thermostat, we put fresh coolant in the truck. After driving back home for about two hours the engine overheated and I pulled over to see coolant/water exiting from the expansion tank, (the lid was blown off but still connected by the little hinge.) My dad came to the rescue with water and I was able to make it home. I then bought unmixed coolant and put that in my truck as it would leave the expansion tank over time. Ever since then I have to keep putting coolant in my truck about once a week depending on how much I drive. Also, after replacing the thermostat we also replaced the radiator cap. I really don't think the issue is the radiator cap but I might as well replace it just to make sure. Whenever I pull the radiator cap off when the tuck has been running for a while I can hear and see a little bit of gas escaping from the radiator. I'm just really confused because the exhaust gas test didn't come up positive and I tested it two times, the second time at operating temperature which is how it should have been done in the first place.

Do you guys know where the temperature sender unit is at on these 2.7L trucks? My Dad spoke to his buddy and he was saying that there could be a small leak via the temperature sender unit. I'm going to have the truck looked at by a professional if I can't figure out what the issue is but I'd like to really figure it out on my own for the experience.

 

Here is the location you seek rear of the engine behind the intake manifold:

 

Even though the block test passed it could still have a slow headgasket leak.

 

Or a leak that only shows up when hot

 

Thermostat is in correct, right?