Put in new temp sensor and thermostat also flushed system.
Temp reading on dash constantly says LO. Even when car gets hot and water backflows from Radiator to overflow. After flushing system when refilled Antifreeze started the car and after a couple minutes the Antifreeze started coming back up out of the Radiator instead of pulling down into system

 

Are you sure the thermostat is opening?

 

Thermostat is working and is brand new 180° just put it in today.

 

OP...hard to tell what you're actually saying....but as the engine warms, coolant is supposed to "back flow from the radiator to overflow".

 

I have a 86 serpentine belt engine someone told me that there's 2 different water pumps depending on if you have serpentine system or multiple belts and that the pumps rotate in different directions but not sure how true that is or how to tell which pump is on the car. But it does seem like when the car is running the antifreeze pumps out of the car

 

I understand it will back flow to reservoir but not to the extent of overfilling it and steam from under the hood

 

Its actually pretty hard to put the wrong water pump on a C4, the pulley has a different bolt pattern then the others. Sound like you have air in the system, I like to pull off a heater hose when filling the system to purge air out of it.

 

there is no stock 86 with multiple belts

 

It is possible that there is a small rupture in the head gasket allowing exhaust gasses to enter the
cooling system. This will force super-heated coolant into the reservoir, and then into the over-flow
bottle. If the siphon system is not working, that would confirm a ruptured head gasket, or at least,
air entering the cooling system.

There is a simple test kit available at most auto stores that will test for exhaust gasses in the cooling system.

A ruptured head gasket doesn't mean there has to be coolant in the oil, or coolant out the tail pipe.
It could just be exhaust into the coolant.

 

I'd start by checking or replacing the radiator CAP....then I'd test for combustion gasses in the coolant.

 

Your car is an '86, right?

Surprised, I'd suspect the temperature sensor first. Measure the temp at the water hoses, base of the sensor and radiator.
Heck, top pipe to the heater core too. Bet they are all over 130F easy, sensor should show something, even if sitting in air.

 

From what i have found out so far this 86 has or had 3 sensors one under plenum beside thermo housing. One between 1 and 3 plug and one between 6 and 8. Between 6&8 gives temp reading on dash. 1&3 kicks on fan. Under plenum must talk to ECM. I wired fan to a switch so can turn on and off whenever. Previous owner took out sensor between 6&8 and put in a plug so i ran wire over and behind distributor and hooked it to NEW sensor between 1&3 now i actually get a temp reading on dash. Now just wanna check that reading is accurate and i believe got some air in the system so gotta jack it up in front try to resolve that.

 

Please be specific, how hot is the engine coolant at the thermostat outlet when the "car gets hot"? Use an infrared thermometer (the "point and shoot" type) to measure the temp at the thermostat housing, or on the hose just out from the thermostat housing. It's important to know the actual coolant temperature.

The gauge reading "LO" sounds like a bad coolant temperature sensor or the wrong coolant temperature sensor for the gauge. That's the one on the head between #6 and #8 plugs. I believe the correct sensor is AC Delco 213-4793 or GM 88865046.

I also think this sounds like air in the system.

Best way to fill that block with a thermostat that doesn't have a "jiggle pin" or small hole drilled in the flange is to pull the coolant temperature sensor right by the thermostat housing. Then fill the thing with coolant until the coolant comes out the hole for the temperature sensor, then install the temperature sensor and finish filling the radiator with coolant. There are other alternatives, but that's the easiest way I've found when using a thermostat that has no "bleed hole"/"jiggle pin."
To the last point first, there's no need to jack it up to get the air out. Simply remove the coolant temp sensor by the thermostat and fill it with coolant until it runs out that hole, then reinstall the sensor. Easy peasy. A

Wiring the fan to a switch is usually a really bad idea. It's a good way to overheat the engine, or to damage a fan motor by leaving it running at highway speeds.

The sensor for the gauge is AC Delco 213-4793 or GM 88865046. The stock radiator fan switch is AC Delco D1852B/GM 14043276. However, that switch has a very high "turn on" and "turn off" temperatures. It turns on over 230°F IIRC. A better choice for the radiator fan switch is AC Delco D1855B/GM 14043275 which turns on at 215°F and back off between 200°F and 205°F. Tell the guy at the parts counter you have a 1990 Camaro with the 5.0L engine to get that sensor.

If you want an override switch to turn the fan on anyway, you can tap in to the wire at the switch on the head and run that wire to a switch and ground the other side of the switch. Turning on the switch grounds the fan relay and activates the fan. I do not recommend running without a coolant temperature switch in the system to activate the fan, though. Even if you remember absolutely every time (you will forget), you could have someone else drive the car who isn't used to it, or who you forgot to tell about the fan switch, and overheat the engine with serious consequences from that.

Also, the 180°F thermostat may cause more issues than it resolves. The PCM is set up for a 195°F thermostat. It may run rich and could even set codes with a lower temperature thermostat (especially anything lower than 180°F). Even if it doesn't set codes, if you still have catalytic converters, you'll likely have those running much hotter with the lower thermostat temperature, which can cause the temps under the hood (and under the floor) to increase with the lower temperature thermostat.

 

No, no, NO. Why do people say this crap?? It won't run rich. It won't set codes...even below 180. The cats won't run meaningfully hotter -if they run any hotter at all. Under hood temps won't be higher. Where does this **** come from?

Do we realize that on the journey to 195°F, the engine passes through all the temps, from ambient to 194°F?? Do we also, realize that the factory stat on all LT1 cars is a 180°F? And during that operating phase (anything below the "magical" 195°F), does any of the things described above, happen? NO! They don't. And why don't they? Because the tune that is in the ECM from the factory is obviously calibrated for those things to NOT happen.

 

No. There is only one WP, no 86 with mutiple belts.

 

CTS is in front of the engine, and is the ECM's sensor. If the coolant temp is pausing at t-stat opening, the t-stat is working fine.

I would replace the radiator cap with a new one and burp this system. Let the car warm up with the cap off, until the stat opens, at that time use your hand to open the throttle to about 2K rpm or have someone in the car do it, at that time the RPMs will suck the water down, fill it to the top and put on the new cap.

If it is still immediately overheating after that, then i'd suspect a head gasket failure. But I would make sure the space between the radiator and condensor is cleared out of debris.

 

Let's address this from the last paragraph first.

"Do we realize that on the journey to 195°F, the engine passes through all the temps, from ambient to 194°F?? ... And during that operating phase (anything below the "magical" 195°F), does any of the things described above, happen? NO! They don't. And why don't they?"

Yes. You do realize that an engine that leaves the factory with a 195°F thermostat is designed to operate with the coolant temperature in the range from 200°F to 215°F as "normal operating temperature," right? And that if all is working properly and the cooling system is adequate (may not always be true in the C4), an engine with a 180°F thermostat will generally run with a "normal operating temperature" between 185°F and 200°F. On a cooler day, it may never reach anywhere in the "normal range" for a 195°F thermostat. The issue isn't whether the PCM can operate the engine at coolant temps below 195°F, the issue is that it tries to build the coolant temperature up to about 200°F, and with a 180°F thermostat, it may operate entirely in the "warm up" part of the cycle, trying to build the coolant temperature up to "normal operating temperature.

"Do we also, realize that the factory stat on all LT1 cars is a 180°F? .... Because the tune that is in the ECM from the factory is obviously calibrated for those things to NOT happen."

Do you realize that the LT1 engine used a different calibration setup in an entirely different PCM? Do you also realize that the OP here has a 1986 model with a L98 engine, not the LT1 engine? The PCM for the LT1 was calibrated to operate properly with a 180°F thermostat. I doubt that the OP wants to do an engine and PCM (and wiring harness) swap just to use a 180°F thermostat.

Yes, if you re-calibrate the L98 PCM (change the calibration and burn a new EEPROM with the new calibration), you can adjust the calibration for a "normal operating temperature" in the range for a 180°F thermostat. Without changing the calibration, the L98 PCM will try to warm the engine up to an engine coolant temperature of over 195°F.

"No, no, NO. Why do people say this crap?? It won't run rich. It won't set codes...even below 180. The cats won't run meaningfully hotter -if they run any hotter at all. Under hood temps won't be higher. Where does this **** come from? "

If you want to make a bet here, and take actual measurements with both thermostats in the same L98 engine in the same car with a stock PCM calibration, I'll take your money. I've won this bet several times before with several different engines and vehicles.

The reality is that there's no benefit to a 180°F thermostat in a C4 with a L98 engine and a factory PCM calibration. It will cause the thing to run rich and the cats to run hotter. It may or may not throw any codes, but it's not optimal.

The biggest cooling system improvement you can make in the C4 with the L98 is to replace that radiator fan switch with one that turns on at 215°F instead of letting the engine coolant get to 235°F before the radiator fan turns on. Changing that switch actually reduces temps under the hood, and it can improve performance because the engine isn't running up into the "overheating" range of the calibration where the PCM starts taking active steps to cool things down, even if it does result in a reduction in power. That starts happening over about 240°F , which IMO is too close to the fan switch turn on temp with the stock switch.

 

^That^ folks, is some of the greatest horse **** that I've see written on these here forums. It's right up there with Leesvet claiming that the fuel pump doesn't run during cranking. Yikes.

Operating range is establised by GM: ~195 to ~230, by the stat and the fans.

Engines will run FINE, from about -40°F to about 250°F....there are cells or modifiers in the factory map for ALL of that range. The engine can do it!

I have an '89 L98. What bet are you willing to lose? What exactly do you want me to measure? Mine has a 160 stat. Runs ambient temps up to about 175. no CEL, no codes, no issues....runs fantastic. Shall I let you know where to send the money?

NOTE: I never advised, encouraged or suggested to the OP to run a 180°F stat. If I did, please quote where I did that so that I can correct it. HOWEVER, since you questioned the benefit of one, the benefit is more power. Engines make more power at cooler temps. Why do we own Corvettes? Power (among other reasons). So...that is your benefit.

IDK WTF "the biggest cooling system improvement" has to do with your conversation here. If you want to burn your fan out early, have at it.

Finally....have you EVER modified anything in any car?? B/c if you're THIS afraid of a T-stat change...holy ****, man. Geezus.

 

Two more things:

Really. Is this **** for real?? An engine/ECM/harness swap in order to run a 180 stat. That is beyond absurd. I'd be embarrassed to type that garbage out and post it. Yikes.


And HOW is the ECM going to try to accomplish this feat...exactly?? Other than turning the fan on, of course....






.

 

I wasnt trying to stir up crap with my post was just looking for suggestions.