Bizarre Radiator Coolant Issue

I just got done reading the thread "Pink Coolant Leak" and my issue is similar, but not quite the same.

Please read ENTIRE post to know what the symptoms are and what I’ve replaced during troubleshooting

I’ve been working on automobiles for about 50 years. You might call me a middle to upper class “backyard” mechanic. I have an issue with my 05 Tacoma Prerunner 4.0 V-6 (160,000 miles) that I’ve never seen before and seeking advice. The engine is NOT overheating and temps run from 186-196 (sometimes if sitting at a red light for too long it goes to 200). Historically, the coolant in the reservoir has always remained steady at halfway between upper and lower fill lines.

SYMPTOM: excessive coolant in reservoir and bubbles coming into reservoir, (especially after a long drive), positive pressure in radiator, even after sitting for two days.

Back in late 2020 I replaced both main radiator hoses and the thermostat (not OEM), drained the radiator, and both engine coolant drains until it was empty. (The fluid I drained was as clean and pretty as the new stuff, so I know I didn’t have any rust or corrosion). Then I topped off the radiator with coolant, and with engine running, heater on full, I re-filled the radiator to the top, (with Toyota coolant from the dealership) and filled the reservoir so coolant was half way between upper and lower level lines.

About 2 months later, (Jan / Feb) when looking under the hood I noticed that the coolant in the reservoir was almost at the top cap and bubbles were coming out of the “inlet tube”(?) to the reservoir. After the engine cooled down, I opened the radiator cap, and cannot see any radiator fluid in the radiator itself. (Pressure in radiator pushed coolant into reservoir until it could push no more?). I removed the “excessive” radiator fluid from the reservoir and put it back into the radiator, where it filled it back to the top. (an indicator that I’m not losing any coolant.) Take the truck out for a long drive and the reservoir is full again. After a few days of this I began troubleshooting.

If you open the radiator cap after letting the truck sit overnight there is positive pressure, (not much, but enough to hear when releasing the cap) so I’m pretty sure I do not have a leak in the system. Also, I’m not losing any coolant, (having to top off / refill) so that indicates no leaks.

Fearing I had a head gasket leak, I took my truck to a shop where a “Block test” was performed to determine if any exhaust gases were in the radiator fluid, and it indicated there was NONE.

I replaced the radiator cap (non OEM) and no change in symptoms.

I replaced the hose from the radiator to the reservoir to eliminate any air leaks (preventing fluid from being drawn back into the radiator when engine cools)

Replaced the fan clutch (OEM) and ONE TIME ONLY after sitting overnight the coolant was lower than half way in the reservoir. (Thought I had resolved the issue! But it has reared its ugly head again) The new fan clutch has the same “stiffness” when engine is cold or hot, and does not feel any different than the old fan clutch. (Not sure if I got a DOA part?)

On my thermostat, I do not know what the position of the jiggle valve is (if it exists). I’ve read where it’s supposed to be at 6:00, (some say 12:00, but that’s an argument for another day), but in those articles “their” temps are the same as mine, so I’ll assume (yes, I know) that mine is a 6:00.

I’m at a loss, unless I replace the radiator cap and thermostat with OEM parts, and verify the position of the jiggle valve. What’s the possibility that I still have an air bubble somewhere and if so, how do I eliminate it? (Sure wish “they” had put a Schrader valve at the uppermost position!). If this does not help, where could that excessive pressure be coming from?

I’ve had some tell me since It’s not overheating, not to worry about it. But I want it to perform properly. We’re coming into summer here in Florida and I don’t want any surprises!

Thanks in advance for any advice, tips, or suggestions.

 

You have a a head gasket leak.

Yes, I read the whole post. Gases don’t always show up in testing.

 

I concur. A compression test sounds like a good idea. It seems it's not as bad of a leak to where it is overheating but it will become an issue. 05-06 are notorious for head gasket leaks.

 

Well, that's disappointing, but not unexpected. My shop stated that if it was a HG leak, my temps would be a lot higher and I wouldn't be able to drive. "will.i.was" thank you for confirming that in your reply.

So, is it ok to continue with driving it until it becomes a bigger problem? Not interested in pushing the envelope, but if it does not need immediate attention, would be nice.

Thanks all!

TB

 

I am not second guessing if you have a head gasket leak or not but I will send along a link to a bleeder kit that works great to get excess air out of the cooling system. Even if using it does not solve your problem it is a nice tool to have at a reasonable price. Using this kit was the only thing that worked on a 2005 Nissan Altima with excess air in the system.


EPAUTO Spill Proof Radiator Coolant Filling Funnel Kit
by EPFamily Direct
Learn more:

$23 EPAuto Spill Proof Radiator Coolant Filling Funnel Kit

https://www.amazon.com/dp/B01I40ZQWE/ref=cm_sw_em_r_mt_dp_BNJ3Q7SJPS4NNS1TZ2K5?_encoding=UTF8

 

I believe there is also a weep hole for the thermostat that needs to be upright to allow for the air to be bled completely out. I would double check the position on the thermostat as well.

 

I would replace the rad cap with an OE cap (I know you have replaced it twice already)....the fact that you can let the engine sit overnight and there is still pressure in the system the next morning, and the overflow reservoir is over full, not letting the vacuum created as the system cools to draw coollant back into the radiator, suggests to me the cap is not working as designed.

 

Almost sounds like when the truck is hot it’s putting fluid into the expansion tank as it should. But when the vehicle cools it’s sucking air instead of coolant back into the radiator.

Is the tube from the radiator to the tank fully inserted (to just slightly above the bottom) of the tank? Also look so at that tube. It could have a pinhole or crack nearer to the top of the tank.

 

Seems like a HG leak to me. Unfortunately it is an expensive repair. I have not done one on a Tacoma and believe that it certainly may be beyond "shade tree" mechanic skill, but if you have the tools, time, and inclination than it will be worth the trouble to do it yourself. First though I would try a sealer. I have used K-Seal in the past on several vehicles with really good results. I know that some (many?) will tell you not to use any kind of sealer, but as you can't be more broken than broken, a $ 15 fix vs a 1500 head gasket replacement seems worth a try. Good luck!

https://www.kseal.com/products/k-seal

 

Therein lies the rub. I've read that the manual states "12:00", but others report a drop of 10 degrees with the weep hole at 6:00. It would be interesting to see where mine is currently. Perhaps I'll investigate this weekend and report back....

 

I've been thinking the same, but believe I never create a vacuum, instead, the cooling system has a positive pressure. But, I could be wrong. (It's been known to happen!)

 

I believe the tube is clear (no obstructions). I was thinking along these lines and using the overflow hose disconnected at the radiator, used a syringe to pull fluid up into the syringe to verify it was not obstructed. I cycled fluid through the line just as a good measure. No obstructions. Hose was also replaced to eliminate any air leaks preventing the vacuum (IF I have one) from working properly.

 

I have the tools, time and talent, but not the inclination. (NOT trying to be sarcastic), I'm not convinced I have a leak since two days later I still have pressure in my cooling system. Run the engine today, let it sit two days, loosen the rad cap and I get a "hiss", (pretty sure it is positive pressure, but no way to actually verify it!)

I'll replace the rad cap with OEM tomorrow and report back.

 

Thanks all for your inputs! They are very much appreciated!

TB

 

If you are familiar enough with twin cams (shade tree levels) working on a longitudinal RWD V6 is not bad.

I've met a lot of people who surprised me taking on their traverse Hondas with rear piston ring problems. Cheapskates, LOL.

edit: It's your headgaskets (prob. just 1 right now) I would bet on it.

 

- non-OEM thermostat [and gasket]
- non-OEM radiator cap
- didn't read manual or ask someone about where the jiggle valve should be

 

It certainly can pay to check cheap things first.

 

Didn't know about any jiggle valve until I had this issue. AND, what's your input as to the direction? 12:00 or 6:00? Seems there is still confusion about it even on several websites. Do I go with 12:00, even if it causes the temps to go up by 10 degrees? Or do I go with 6:00 for the lower temps? (This is the conclusions I've come to reading various threads on the subject.) Yes, I know the manual says 12:00, but even Toyota can encounter a type-O once in awhile. I'm not interested in the 12:00 vs. 6:00 argument, but like everyone else, was there ever a definitive answer?

 

If your replacement non oem radiator cap is a Stant, it’s probably good. But who knows these days. Brands you’ve trusted for years will sell out, now your buying a Chinese part.

It sure sounds like an issue with the radiator cap not performing correctly.

 

if you have a plugged over flow hose or bad rad cap, the rad hoses will be collapsed (indicating vacuum created as system cooled down)
if you squeeze the upper rad hose before opening the rad cap and its hard, it would be pressurized which can point towards faulty cap too, I have never seen a bad head gasket that created pressure in the rad hold that pressure over a couple days...pressure has to drop to zero because of rad cap

another trick to confirm compression gasses entering rad system is hook up a rad pressure tester, (dont pump it up) start engine raise rpm if pressure gauge rises quickly or needle move back and forth rapidly you have a headgasket/compression gases issue.