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TBI Running Hot

Not all L05 heads are 76cc. 76cc heads only came on 4 bolt HD 350s 3/4 and up trucks. If you have a 2 bolt main 350 you should have 64cc heads
But who knows what heads jasper put on your engine. Only way to tell for sure is pull the valve covers and check the casting numbers in the lifter valley. Or look at the casting marks on the front of the heads. 64cc Heads have 2 parallel casting marks just below the valve covers. They look like captains bars.

Stock timing on TBI engines at idle without the timing bypass disconnected is usually around 18-22 degrees. If you cant find the timing with your gun set at 25 degrees it seem a little high to me.
You did set the base timing with the timing bypass disconnected. RIGHT?
 
I didn't realize there was a difference in L05 heads. I know the block is 4 bolt because it came with no pan. I ordered the motor for a 1990 K3500 because I knew it would be a 4 bolt main motor. I would presume then that the heads are 76cc but like you said who knows what they slammed on there.

I did do the bypass when I set the timing. With the chip it is really touchy. If it's not a zero degrees with the bypass it either idles too fast (advanced) or surges (retarded). It seems like something as small as a degree will make the difference.

I didn't go moving the heater core hose yet because I've determined it would be a pretty good rig to do so. I did however come up with a brain fart and noticed that the coolant sensor that runs the ECM is directly next to the thermostat....so I plugged my laptop in with WINALDL and watched the temp fluctuation. Looks like my presumptions were right (if you trust the sensors) because if you just hop in the truck and drive it cold the gauge quickly runs up to 240deg where the sensor for the ecm is still running about 120deg. In other words there is lag time from when the thermostat area gets hot and the heads are hot. I tried both banks because I have sensor in both heads and the results were the same. Now, if I simply let the truck idle up to warm the lag is very minimal..something like heads 190deg when thermostat reachs 170deg.

One other anomally I noticed performing this was that until the thermostat did open the belt on the water pump was under a ton of load. Not really squeaking but kinda like a flat tire on pavement noise...well without the thumping. Soon as it opens noise is gone. If nothing else this tells me that that thing is building a ton of pressure before it opens.
 
Sounds like a problem I was having on A new GMPP crate motor with vortec heads. The problem I had was that the engine was building up a lot of pressure under the thermostat and keeping it shut. It would heat up so quick it was ridiculous. Turns out with the vortecs they have no coolant cross over, so there was no way to alleviate the pressure under the thermostat by being linked to the water pump. I ran a hose from the bottom of the intake to the water pump, fixed the problem. I had one heater core hose running from the intake, and also to the radiator.Eventually to get rid of that little weird looking hose I capped off the radiator and ran that one to the water pump. I have been running it that way for a long time now and works great.Before that I tried every thermostat imaginable, even a MR. Gasket HI-FLO 180*, that worked but ran the engine soo cold that it was building up carbon and fouled out plugs. Don't do that.

Try moving your heater hoses around and see if that helps any.
 
try puttin in a 160 t stat or just run a stat with all the guts removed so there is still some restriction
 
when ever i do an engine swap, and i have done to many to count, and all were sbc's. when i have all the coolent removed from the system and then go and refill the cooling system i dump in 4 liters of 50/50 and then fire the engine, let it run for a bit and gradually add more coolent, while doing this i rev the engine, and also squeeze the coolent hoses every so often to help move the air out of the system. when you said that you had a big burst of water come out the rad cap, likely what you have was a case of hydrolic lock, meaning air in the system, run the motor with the rad cap off for a while but don't fill the rad right up to the top.
 
Ok, well i just got off the phone with Brian from TBI chips and he offered me some insight on the topic. He said typically he doesn't see this behavior, but he has in the past. He isn't quite sure what causes it internally (core shift, crossover flow etc) but that's really an aside. The problem as he explained it is that the chip does run an aggressive curve, but, but, it runs a much more agressive curve when it recieves cold coolant temperatures form the ECM sensor (because it can get away with it when cold). Stepping back a bit, my ECM sensor is in the intake manifold not in the head (I looked at my '87 and the ECM sensor is in the head, there is no-way the '90 sensor was ever in the head because the leads are super short and the ground goes to the coolant neck) and I have already determined that the heads are way too hot before that sensor get up to temp. What he recomended was to move my ECM sensor to a head port thereby keeping the ECM from advancing the timing. I think this may well be a plausible solution. All else fails he said log it with ALDL and he'll re-burn a chip that will run cooler. I don't how the guy finds the time but that is a AOK response in my book.
 
Does anyone know if there is a difference between the temp sensor for the ecm and the temp sensor for that gage found in the heads on these motors. The one for my ECM has 2 wires, but one is a ground and I'm guessing GM did this because it's in an aluminum intake? I was wondering if I could simply use the single wire coolant sensor I allready had in the head to test this theory.
 
pseudomike said:
Does anyone know if there is a difference between the temp sensor for the ecm and the temp sensor for that gage found in the heads on these motors. The one for my ECM has 2 wires, but one is a ground and I'm guessing GM did this because it's in an aluminum intake? I was wondering if I could simply use the single wire coolant sensor I allready had in the head to test this theory.
Click to expand...

The coolant temp sensor and the water temp sensor are different sensors and cannot be interchanged.
 
The ECM monitors the voltage that goes through the ECM temp sender, which is why there are two wires...a constant voltage "feed" and a "return". Same reason TPS uses multiple wires.

Gauge sender is simply resistance to ground.
 
Well, definitely made "a difference" but I wouldn't call it the end all. With a 170deg stat I still tapped 190-200 degrees from dead cold w/no warm up. I've decided I'll have to live with a holy thermostat for now, so back to an 1/8" hole in a Stant 180deg heavy duty. Truck runs flat as a board at 180deg with this setup. No spikes, no cycling so I guess I really can't complain. I'm just wondering what happens if a piece of calcium or something ever plugs the hole? Well, hopefully we have a new power plant together before then.
 
was the fan replaced at all? could be a standard rotating fan causing the problem. had that happen in the burb. should be a reverse rotating fan. if its pushing air out the front its the wrong fan. sounds like a sweet motor other wise.
 
It's got both an electric and the factory fan. Both are pulling air through he radiator. Should have no problems cooling when they both come on. The motor pulls good, too bad for these problems.
 
my 90 k5 did the exact same thang and the only thag that i could get to stop it from runnin hot was like you said was to drill a small hole in the T-stat.
 
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