Almost met Jesus this AM due to a faulty thermostat!

[SquareRoot]

That's my theory anyway. Maybe someone can give me a sanity check. So on the way to work this morning I am going around a bend in the road at about 45 mph when all of a sudden I had no brakes or steering. Thank the good Lord there was no oncoming traffic in the opposite lane cause I shot into it trying to get stopped. Apparently, when I let off the gas the engine died and I didn't realize it. A dead engine and hydroboost make for a hell of a workout! Luckily I turned the key and she fired right back up and life went on. Wondering what happened, I opened the efi app on my phone to see if something weird was going on with the IAC. Everything looked good, then I noticed the coolant temp. Huh? 149? That can't be right. Nope, the Dakota Gauge says 151. Two gauges and different senders say the same thing. How the H*LL can that be with a 195 thermostat? Now granted, it was 41 degrees outside, which is cold for us desert rats.

I drove the remaining 20 miles to work without issue except for the mess in my shorts however, the coolant temp never got above 158. So-I'm guessing the thermostat took a crap and is failed in the open position? When I got to work, I let it idle and it slowly got up to 197 and stayed there without the fans on.

Am I crazy or is that the only thing it could be?

 

[gmbellew]

not sure why the engine died, but definitely seems like the thermostat is stuck partially open.

 

[squaredeal91]

Wow I've had engines die when letting off but nothing quite like this? I understand you probably have a bad stat but I don't know if that's enough. I would think maybe knock sensor? Or distributor component is now giving you its first warning? Glad it ended well and nothing happened.

 

[SquareRoot]

Wow I've had engines die when letting off but nothing quite like this? I understand you probably have a bad stat but I don't know if that's enough. I would think maybe knock sensor? Or distributor component is now giving you its first warning? Glad it ended well and nothing happened.

No knock sensor. If the temp is below 160 it runs in open loop and based on the fuel map that's programmed. I'm not sure that I have ever tuned the map at this temp before so it might be lean. It's rare to get 40 degrees here.

 

[ChuckN]

Sounds scary! Just glad you’re ok.

Do you feel like it went into some kind of limp mode? That sounds weird.

 

[squaredeal91]

No knock sensor. If the temp is below 160 it runs in open loop and based on the fuel map that's programmed. I'm not sure that I have ever tuned the map at this temp before so it might be lean. It's rare to get 40 degrees here.

That all makes enough sense to be the culprit. Coolant temperature has allot to do with everything lol

 

[HotWheelsBurban]

That's my theory anyway. Maybe someone can give me a sanity check. So on the way to work this morning I am going around a bend in the road at about 45 mph when all of a sudden I had no brakes or steering. Thank the good Lord there was no oncoming traffic in the opposite lane cause I shot into it trying to get stopped. Apparently, when I let off the gas the engine died and I didn't realize it. A dead engine and hydroboost make for a hell of a workout! Luckily I turned the key and she fired right back up and life went on. Wondering what happened, I opened the efi app on my phone to see if something weird was going on with the IAC. Everything looked good, then I noticed the coolant temp. Huh? 149? That can't be right. Nope, the Dakota Gauge says 151. Two gauges and different senders say the same thing. How the H*LL can that be with a 195 thermostat? Now granted, it was 41 degrees outside, which is cold for us desert rats.

I drove the remaining 20 miles to work without issue except for the mess in my shorts however, the coolant temp never got above 158. So-I'm guessing the thermostat took a crap and is failed in the open position? When I got to work, I let it idle and it slowly got up to 197 and stayed there without the fans on.

Am I crazy or is that the only thing it could be?

Yup hydro boost failure is not fun at all!!!!
Had this happen twice on my crew cab. First time, the unit failed and blew its seals, second time the idler pulley froze up and took the belt out. We live on a major highway in Houston, near a major freeway intersection, and were coming out the RV park gate when the hydro boost unit let go. Had to manhandle it outta four lanes of oncoming traffic and down to the other gate, then get it parked where a wrecker could get it the next day.
When the belt broke, we were idling at an intersection; once the light changed, got it into the parking lot and parked, hoping it wouldn't overheat before I got it across the lot to an open area. This is important with 21 feet of truck to park.... Fortunately I was able to figure out what happened, and buy the belt and idler pulley from the O'Reilly's a few blocks away.
More to your point, sounds like a bad thermostat to me.

 

[Vbb199]

Whats the present in/hg or map kPa?
Either at idle

 

[SquareRoot]

Whats the present in/hg or map kPa?
Either at idle

15-16

 

[Vbb199]

15-16

Im trying to think of some other reason it did that other than if it was running below the specified CL temp,its gonna probably be in some sort of OL enrichment the entire time, making it load up and be gassy. But only being a little off from say, 160-190 wouldnt make it run that badly. Is there a target AFR for that thing based on coolant temp?



and with the air temps being real cold, it might be putting more than usual timing in it, assuming the IAT offsets are setup in the EFI.

 

[SquareRoot]

Im trying to think of some other reason it did that other than if it was running below the specified CL temp,its gonna probably be in some sort of OL enrichment the entire time, making it load up and be gassy. But only being a little off from say, 160-190 wouldnt make it run that badly. Is there a target AFR for that thing based on coolant temp?



and with the air temps being real cold, it might be putting more than usual timing in it, assuming the IAT offsets are setup in the EFI.

AFR is irrelevant until it goes into CL above 160. In OL, it's all based on what the map is programmed too. For the most part I have populated that map based on drivability. My guess is it's lean at idle based on temperature. Like I said, today may have been the first time it's experienced these cold conditions so I didn't know it was lean. I'll bump up the idle fuel a bit and see if it happens again. Once it's in CL, the AFR setpoint will do it on it's own. It usually hits 160 pretty quick. Without the thermostat issue today, it has never happened. It's fascinating learning how EFI works.

 

[SquareRoot]

UPDATE:
Just to follow up on this. I pulled the stat out this weekend and threw it on the stove in a pot of water. It opened at the correct temp and closed as it cooled down. Upon close inspection I found a small piece of rubber lodged between the piece that moves and the body. The piece was about 3/8th long and about the thickness of a piece of yarn. It was enough to keep the stat from closing that last itty bit. This is a high flo version stat. I was skeptical that itty bit of opening was the culprit but I replaced it anyway. Afterwards the engine got to 195 and stayed there as it should. One thing I did notice is that the colder the engine the less effective the catalytic convertor is. 150*= stinky, 195*=no stinky.

 

[squaredeal91]

Do you have a aluminum radiator plastic tanks? That's probably where the rubber came from. I remember pulling a bunch of it out of a radiator once that wasn't even leaking, just was coming apart inside.

 

[Sgt Gus]

I've seen my dear old Dad put the Stat on the stove. Glad your ok, scary. I better prepare my daughter for potential situation since it's her truck. Pulled off the t-stat yesterday on our build and had a 180° motorad in it. Think I'll put a high flow 195° ACdelco in when putting back together.

 

[SquareRoot]

Do you have a aluminum radiator plastic tanks? That's probably where the rubber came from. I remember pulling a bunch of it out of a radiator once that wasn't even leaking, just was coming apart inside.

My rad is 100% aluminum. I'm about 98.2% positive the small piece of rubber came from the rubber seal on the inside of the radiator cap. I noticed it had started disintegrating and it got replaced as well.