Chasing Overheating Issue...

Hey everyone, second time posting but long time listener.

I am chasing a seasonal overheating issue for two years now and could really use some help before I loose what hair I have left. I have a 2015 Tacoma 4.0 and live in AZ. Here is the story...

Mid July two years ago I was sitting in the kids schools parking lot waiting to pick them up when I noticed the A/C getting warm. Looked at my Ultragauge and notice the temperature was upwards of 215* - 220*. Immediately turned the heat on and revved it up to lower temperature. After doing some testing I found that the truck will overheat only when in drive and the A/C on.
I performed a cooling system pressure test and after 30 minutes and lost 2 PSI (engine cold). After consulting with a Toyota tech friend he said it might be a head gasket but start with the cheaper fixes first. I replaced the thermostat with no change then proceeded to replace the fan clutch, radiator, radiator hoses, radiator cap (tried stock and TRD) and water pump. At this point still no change. Finally, I accepted my fate and decided to do a head gasket. I discovered that #6 cylinder had a minor leak and replaced both head gaskets. Since this task I have a new set of symptoms..

When in drive and A/C on the temp will take a long time to go up but will accelerate if I drive on the freeway and then go to surface streets and stop. In town my truck will run at 199* - 203* while on the freeway it will be between 204* - 208*. Also the ambient temperature does play a role in this as well. It seems that if the temperature is 95*ish or higher than the truck has cooling system issues. I did just replace the engine temperature sensor, tensioner pulley and belt 2 weeks ago. All parts that have been replaced are Toyota parts. After the recent replacement of parts I redid the cooling system pressure test for 2 hours and did not drop 1 PSI.

This truck has stumped everyone that has looked at it. It has a BRAND NEW cooling system, could it be something outside the cooling system causing trouble? I basically at the point where I am throwing parts at it hoping something fixes it lol.

**On an interesting note, when draining the coolant into a pan I have noticed a ring of sand in the liquid that formed at the bottom of the pan (pan was thoroughly scrubbed before use).

 

To start simple, is the system fully burped without any air?

Everyone says these are hard to fully purge all the air out. I did a drain and fill on my coolant a few weeks ago using the

$19 Lisle 24680 Spill-Free Funnel, Standard Adapters, 11 x 7 x 7"es

Lisle 24680 funnel and all seems to be good so far.

 

I assume you used the OEM coolant pre-mix at least 2 gallons.
Did you open the block drains on each side and flush all the old coolant and crap out?
Does you dash gauge show a big change in temp too - is that how you saw the overheating?
If only when in drive with AC on does the idle increase as it should (AC off then on try it) handled by the ECU.
Someone should know that circuit on TW and what to check.

 

I feel that it is purged of air, heater is blistering hot. I used a funnel just like the one you mentioned. Jacked the front end of the truck up so the radiator fill was the highest point then got to operating temp. Revved up to 3k rpms until bubble stopped coming out into the funnel and heater was super hot. Let the truck cool down with funnel on.

 

- Yes, only Toyota parts and coolant have been used.
- The dash gauge only moves when it gets to about 220*. I have seen it go up to the 3/4 mark before I did the head gasket. I use my Ultragauge to give me a more exact engine temp.
- Yes, I can feel the idle change and I put the rpm readout on the Ultragauge and saw a 200 - 250 rpm difference.

 

If it’s only in drive as well, are you able to view trans temps? Does the truck have tow package (trans fluid line runs through the radiator to cool it off)?

Possibly the trans is somehow getting too hot and inducing too mucin heat into the cooling system.

 

The truck does have the tow package. Trans temps are about 180* - 200* in town and can get up to 230* climbing hills on the freeway. I was thinking that as well but it is just a 8" small diameter tube. Can it transfer enough heat to over take the cooling system? I can always delete the radiator connections and connect the tubes together to test it.

 

No those ATF temps are fine IMO for the ambient conditions you are in down there. I wouldn't mess with that.

Another simple suggestion: Is the rad plugged with mud? If you do any sort of regular off roading youll be amazed how much silt and fine mud can collect between the fins of the radiator. The AC condenser takes the brunt of it, but that still restricts airflow. Start with a regular garden hose and try to spray from back to front (easiest if you take the whole fan and shroud off).

 

I do a good amount of off roading and hose out the condenser/ radiator every time I wash the truck. I test this idea by putting a flash light on the engine side and looked through the outside, could see the light clear as day.

 

95 deg ambient is hot af. Your cooling system is doing everything it can to keep engine temp around 200.. sounds normal to me

 

95* is nothing for AZ, we are projected to be 118* today lol.

 

It still should be able to stay at normal temps in that.

 

Agreed, it was doing it before just got to figure out what happened.

 

Did you try a leak down test on both heads? Are you losing any coolant? When you jacked up the front end, are you sure no air got caught in another high point such as the heater core resulting in still having air in the system?

Simple questions, but they may help someone else out too. I know these air conditioners aren't the best when not moving in high temps due to the non-electronic fans.

 

I didn't do a leak down test, was debating on it as the cooling system held 18 PSI for 2 hours when I did a cooling system pressure test. Coolant levels are staying consist, I have my reservoir marked for hot and cold coolant levels. I cant guarantee that there was no air in the heater core lines but both hoses were super hot and heater was pumping out some blistering heat. I can try to crack open the heater core line splice ever so slightly and see if I get any air out.

I was wondering if it has anything to do with the A/C as the overheating issue happens when it is on. A/C blows really cold though...

 

Coolant temp around 200 with A/C running and it's 95+ outside is asking a lot of the cooling system. Hell, living in AZ is asking a lot of the cooling system

Cooling temps fluctuate, there's a reason the gauge doesn't move until 220+

Just because the thermostat opens around 180-190 doesn't mean the temp is going to always stay at 180-190

 

What about your AC compressor? That seems to be the only variable left, but it would seem odd to me that any additional drag beyond normal would cause overheating.

The sand is somewhat interesting. If there was casting sand left in the block, maybe it accumulated in a particular spot and is blocking some flow somewhere? That would be nearly impossible to find, and I'm assuming there have been flushes of the system during the other parts changes.

 

I live in Tucson - we are having the same heat wave minus about 5ºF. We are slightly higher elevation. If I drive with no AC at 105ºF the temp stays down below 190ºF. Ordinarily stays at 184-186ºF up to about 100ºF ambient. AC in slow moving city traffic at these current ambient temps - starts to climb.......

It would help if there was a little more fan flow in this outfit and I would buy one if it were a straight replacement. Not interested in the Toyota "additional fan" fix.

 

V6 Coolant Change how-to

I took this from the above post which is an excellent read by the way. In the picture I linked, you will see a large hose. That hose needs to be squeezed while the engine is warming up to burp the air out of the system. It will get hot as the engine is warming up so you might need to use some mechanics gloves. Also, I have heard of people drilling a small hole with the smallest drill bit, like a 13/64th, through the top of the thermostat to allow air to flow back even if the thermostat is closed. I personally haven't done this. Lastly, are you certain that 'stop leak' hasn't been used in your coolant? You mentioned something like sand in the drain pan. Stop leak is like tire slime, it'll get you to repair facility but the damage it does to your system typically is more than the benefit of the stop leak. It clogs up the passages in your radiator.

I like posting Chrisfix videos since he's pretty easy to follow along if your mechanics skills are in question.


It's not specifically for the Tacoma, but the principals are the same. We do have the block drains on each side (if you're V6) so reference the link above.

-J

 

you can always go out and get high flow dual electrical fans and put them on