1987 Chevrolet 350 tbi high idle

gmbellew · Nov 27, 2021

if your running hot with a proper thermostat, your fan clutch may be getting weak or your radiator may be partially plugged up if the hoses are OK.

iamtherealJayy · Nov 27, 2021

I’m pretty sure it ended up being the upper radiator hose, I changed it too since it was older when I threw in the 160 t-stat. It was pretty hot outside so I wanted to keep it cooler, but now in winter I’m fine with it running 195, it never overheated on me it just took too long for the thermostat to open and the gauge was reading roughly 230-235ish before it would drop and it never gave me trouble I just didn’t like it getting up there because you really had to watch it and make sure it came back down.

AuroraGirl · Nov 27, 2021

There are two operation modes for CCC System: closed loop and open loop fuel control. Closed loop fuel control means the oxygen sensor is controlling the carburetor or throttle body delivered air/fuel mixture ratio. Under open loop fuel control operating conditions (wide open throttle, engine and/or oxygen sensor cold), the oxygen sensor has no effect on the air/fuel mixture.

On some engines, the oxygen sensor will cool off while the engine is idling, putting the system into open loop operation. To restore closed loop operation, run the engine at part throttle and accelerate from idle to part throttle a few times.

In the morning when the engine is cold, if the system keep the air/fuel mixture at the 14.7:1 ratio, the engine wouldn't run very well. When the engine is cold, it has to have a richer mixture. An automatic choke is used to give the engine a richer mixture until it is up to normal operating temperature. In addition to the choke, a temperature sensor located in the water jacket of the engine is used by the ECM to monitor engine temperature. When the temperature sensor signal indicates that the engine is cold, the ECM will ignore the oxygen sensor signal

@Rusty Nail isnt wrong when he said the thing about the coolant temp. Its the truck trying to warm up, the idle. your ECM wants it at temp and it cannot get to temp.

AuroraGirl · Nov 27, 2021

iamtherealJayy said:
I’m pretty sure it ended up being the upper radiator hose, I changed it too since it was older when I threw in the 160 t-stat. It was pretty hot outside so I wanted to keep it cooler, but now in winter I’m fine with it running 195, it never overheated on me it just took too long for the thermostat to open and the gauge was reading roughly 230-235ish before it would drop and it never gave me trouble I just didn’t like it getting up there because you really had to watch it and make sure it came back down.

air in the system.

AuroraGirl · Nov 27, 2021

Remember you can check the open vs closed loop status by simply doing Field Test Mode by grounding the two pins you use for the codes WHILE the engine is running and then driving. The flashing will correlate to the status. And your truck at idle is going ot have a cold catalyst according to its calculations so it will probably show open loop. Try driving and seeing what it does . Quick accel will be open loop no matter what

gmbellew · Nov 27, 2021

I don't know what the exact CTS and O2 sensor temperatures are to hit closed loop. but it is less than 160 degrees on the CTS if the O2 is up to temp. I'll try to pay attention next time if I think about it.

iamtherealJayy · Nov 27, 2021

I just went on a fair journey running about 60 for maybe 6-7 minutes straight after the thermostat had already opened and it was up to temp and all of a sudden I checked the gauge and it was reading 210, let out of the throttle and it instantly started going down. It is still running the 160 thermostat and hasn’t given me any problems in several months. I don’t want to go back to a 195 if it’s going to start running hot again.

gmbellew · Nov 27, 2021

210 isn't what I'd call hot. a 195 degree running temp is only 15 degrees away from 210 under load in hot weather. 230 and up is starting to be hot.

the thermostat sets the minimum temperature. your radiator and cooling system, in conjunction with ambient air temp and how much load is on the engine, determines the maximum temperature.

iamtherealJayy · Nov 27, 2021

Hitting 210 with a 160 t-stat is a bit hot in my opinion, Since it’s around 50° outside currently. I don’t know why all of a sudden it would get up in temp like that. I reckon I’ll do a 195 and re bleed the system since it’ll loose a little coolant while changing the thermostat. Hopefully no more running hot and then I can start checking the iac for issues. I’m going to get a can of carb cleaner while I’m getting the thermostat and start by cleaning the iac.

skysurfer · Nov 27, 2021

What's the history on your radiator?

iamtherealJayy · Nov 27, 2021

Radiator is less than a year old, truck got parked for 6 years due to overheating(they thought was head gasket) it was lower radiator hose, I have replaced lower and upper hose and the radiator and heater core. The only coolant hoses that have not been replaced are the heater core hoses. I picked up a 195 thermostat new gasket and gasket maker just incase. Also got carb cleaner to clean iac tomorrow since it’s now been dark for several hours. I’ll disconnect the battery as suggested while changing thermostat then bleed cooling system and see if idle comes down. If not move on to cleaning iac and possibly replacing.

AuroraGirl · Nov 27, 2021

iamtherealJayy said:
Radiator is less than a year old, truck got parked for 6 years due to overheating(they thought was head gasket) it was lower radiator hose, I have replaced lower and upper hose and the radiator and heater core. The only coolant hoses that have not been replaced are the heater core hoses. I picked up a 195 thermostat new gasket and gasket maker just incase. Also got carb cleaner to clean iac tomorrow since it’s now been dark for several hours. I’ll disconnect the battery as suggested while changing thermostat then bleed cooling system and see if idle comes down. If not move on to cleaning iac and possibly replacing.

I forget if these trucks use a jiggle pin
but if they do make sure its pointed the right direction.

If they dont, drill a small hole on the flange of the thermostat so air can bleed faster. Also how are your belts, they turning the water pump ok? You using green coolant riight? Might be worth cracking a block drain if SBC has a block drain which im actually not sure because I am thinking about my car.. I assume it does. See if debris is setting in there

iamtherealJayy · Nov 27, 2021

All three belts are less than a year old, yes green coolant 50/50 mix, I flushed system when I got it and used concentrate equal parts with water from Walmart so no minerals in it, but after changing thermostat etc I started using the prediluted since I wouldn’t know how much I needed. I’m not sure it has a block drain.

AuroraGirl · Nov 27, 2021

iamtherealJayy said:
All three belts are less than a year old, yes green coolant 50/50 mix, I flushed system when I got it and used concentrate equal parts with water from Walmart so no minerals in it, but after changing thermostat etc I started using the prediluted since I wouldn’t know how much I needed. I’m not sure it has a block drain.

Did you use demineralized water or distilled water? Ones better than the other but both are fairly fine in this situation.i would get a coolant tester and verify your mix is reading right on the thing.

Rusty Nail · Nov 28, 2021

Been a pritty good show SO FAR but, where's the pix man?

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1987 Chevrolet 350 tbi high idle

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