2008 Tahoe Hybrid Engine Temp Rises in Auto/Stop

[Dirtrunner702]

Hello!

The engine temperature needle goes past 210 when the Tahoe enters into Auto/Stop. The temp levels out and stays right at 210 when the engine runs. Coolant reservoirs are where they should be at.

My first thought is that the little auxiliary pump motors that are in-line with the mechanical water pump hoses may be shot but wanted to ask if anyone else had seen this issue and if it was the auxiliary motors. I went to look up the replacement motors, but they are labeled as Drive Motor Inverter Cooler Water Pump. I'm not sure if that has to do with keeping the Engine coolant flowing when in auto stop or not.

Any insight would be appreciated!

-EDIT
I realize that there is an electric motor underneath the coolant reservoir so perhaps thats the culprit?

 

[j91z28d1]

there's 2 I believe. one flows the coolent in the separate hybrid system but is hard to tell which is which between the 2, the inverter cooling system and the other is in the normal cooling system to keep it circulating during auto stop. I thought it was for heater but it may also help with heat soak which might be what you're seeing.

I haven't paid much attention to temp gauge except when it's been cold and heat running. I am pretty sure the temp dropped while in auto stop and the hater blasting.

if I get out in it later today I'll watch and let you know.

just as a guess since you're not getting a code for the inverter temp, I'd say that one is fine. if you can test the other one, that might help. might even be a fuse for it? I've not gone down the rabbit hole on the pumps. yet since mine haven't failed and I have a stack of parts to replace common failure stuff soon ish. but it is possible a good 2 way scanner like the tech 2 could activate it to test with the engine is off key on. but again not sure.

 

[j91z28d1]

-EDIT
I realize that there is an electric motor underneath the coolant reservoir so perhaps thats the culprit?

I'm pretty sure that's the inverter pump. if you follow the hoses. I think that comes down off the smaller side of the overflow, which is the hybrid stuff. it doesn't run thru the radiator to cool. it has its own cooler in front of the radiator for it but used the same overflow tank just a split one.

 

[j91z28d1]

so I was bored so I pulled up the manual, I couldn't for the life of me find the electric coolent pump anywhere, wiring, replacing nothing. I know I've seen it on my truck but the software only shows the 2 hybrid inverter water pumps. ones at the middle of the radiator between the fans and the other is drivers side of the radiator. no clue why it has 2 back to back, unless to make sure if one fails you still have a back up. seeing as these trucks do nothing if the hybrid stuff goes down. both of those are on anytime the key is on and wired in parallel off fuse 6.

but I don't think those effect what you're seeing at all. if you look at the belt driven pump, to the left is a electric pump in a heater hose. I can't for the life of me find wiring or reference to it in my software and it's not on the non hybrid ones. I believe if this pump isn't working, it might cause heat soak when it goes into auto stop.

I'd start there, test for power and maybe look for a fuse. if find a diagram I'll post it up. a test that might tell you something is to run the heater, yeah I know it's summer and brutal but maybe at night for a bit, once up to temp turn the heater on max, let it get nice and hot, then go into auto stop and if the air cools off after a few mins it probably means that pump isn't circulating water when the engine isn't running.

here's a pic, it's hard to see without removing the air intake, but you can peek down and see it.






I forgot to ask, but what Temps are you seeing when you see it climb and are you just seeing the dash the gauge move or are you seeing it on a scanner?

 

[Dirtrunner702]

Thanks so much for the input!

The more that I researched I was able to put together that the pump under the coolant tank and the one farther down the line towards the driver side are only for the hybrid component cooling. I'm sure if those failed you would get a warning or message.

The pump that is in line with the heater core hoses may by my culprit. A few months back I was in that area when I found a short in the loom. I made a post about it on here too. I remember seeing the cabling looking a little twisted to the little pump connector. I sort of remember the little pump being somewhat noisy as well. I will be doing some of the tests that you suggested and report back!

Really appreciate the info, brotha!

 

[j91z28d1]

good luck with it, I think I might have found that pump diagram, it's under the hvac, if so it runs off fuse #4 on the aux fuse box.

I don't know when it is supposed to run thou. I believe they called it the aux heater pump.

I drove mine today, the truck said it was 106 outside and it stayed dead middle of the gauge, never moving auto stop or running. but with the ac blasting it only auto stopped few mins, maybe 3 or 4? before cranking. the ac was pulling 12amps. I've not seen it pull that much before. it drained the battery pretty quick.

 

[BG1988]

Hello!

The engine temperature needle goes past 210 when the Tahoe enters into Auto/Stop. The temp levels out and stays right at 210 when the engine runs. Coolant reservoirs are where they should be at.

My first thought is that the little auxiliary pump motors that are in-line with the mechanical water pump hoses may be shot but wanted to ask if anyone else had seen this issue and if it was the auxiliary motors. I went to look up the replacement motors, but they are labeled as Drive Motor Inverter Cooler Water Pump. I'm not sure if that has to do with keeping the Engine coolant flowing when in auto stop or not.

Any insight would be appreciated!

-EDIT
I realize that there is an electric motor underneath the coolant reservoir so perhaps thats the culprit?

DON't let it go into auto STOP

use M4 only tell the electric water pump is replaced you will risk damaging/warping the engine block and inverter ..

could be a faulty thermostat as well dirty radiator

the engine should cool down when in autostop (at lest from my experience)


do both fans spin on high when the A/C is turned on?

 

[j91z28d1]

just to come back around to this.. I saw mine do this today once.

hot restart, outside temp was reading 113, diving a bit and outside temp dropped to 105. more what the actual outside temp was.. stopped at a red light a few miles down the road, was in auto stop for a while, and noticed the temp gauge above the 210 mark. never seen it move.. before I grabbed the scanner and got it connected the light turn green and it dropped right back down as soon as it started.

only time I've ever noticed. drove the rest of the trip with the scanner up and it never did it again.. it would get down to a low of 195 on the highway, and when I stopped. including a drive thru that went thru the full battery it never moved again on the dash. scanner would move up a bit when stopped in auto stop, from 195-199 when driving to 208 at lights engine off. but that's not enough to move the dash gauge at all.


so yeah, interesting. the dash gauge moved a good 1/4inch passed the middle 210 mark. I will try to look deeper into it. just wonder if it was a hot restart kinda heat soak thing. maybe it doesn't actually run the water pumps when in auto stop?

does yours do it every stop or just under certain times.

 

[j91z28d1]

so this was an interesting one.. i took a few minutes to check it out.

long story short, my coolent/heater pump was not working. after some head scratching, I realized my relay was in backwards. how weird. I definitely didn't do that.

just for info, it's a negative controlled relay from the hvac module pin 11. the fuse #4 in front of the the relay will have power when the pump is on but not off. the pump does run any time its in auto stop. but here's the weird thing, when the engine is running, or key on engine off. there's pos 12v on the turn on terminal of the relay block. this is confirmed by the tech 2. under hvac module, go down to hybrid stuff, then look at data. it will tell you when the engine is running that its shorted to + and then when you go into auto stop, it says OK. you get a ground on that terminal and the motor runs. tech 2 reads the same with the relay in, out or backwards. so it's not a feed back thing so it knows it's on. there's no dtcs for this. unless your coolent temp spiked to high and set that one.

I got nothing for that.. but mine definitely wasn't running before, it is now. I will keep an eye on it. but I doubt I'll see a temp spike now. unless there's a reason someone flipped the relay haha.

see pics of tech 2 screen. OK is when the pump is running, the shorted to B+ is anytime its off.

to get into auto stop with hood open, you can command it with the tech 2 or just use a screw driver to latch the hood latch. just don't forget to release it before slamming the hood haha.

 

[Dirtrunner702]

Hey all!
I completely spaced to reply here what I ended up finding the cause of the problem to be.

My thermostats rubber portions had fallen apart and were very brittle. It was allowing water through and causing the system to not work properly, as soon as I took the housing off, there it was clear as day. Removed, flushed the coolant out of the block and heater core, installed a new OEM thermostat and gasket, completed the coolant fill up procedure and the issue went away...
I have since made a note to always consider the very basics before doing anything else on this thing!

Appreciate all your input, you guys are a true gem.