so should have pay a shop to burp my heater core see if that does the trick ?

 

No. I don't think too many shops quite know what to do.... If they cant just hook it up to their machine, or whatever, and "fix" it......

Backflush the heater core if you haven't already, that has worked very well for me.

 

how do you bakc flash the heater core ?

 

Take both hoses off. I used another section of hose to extend the one that hooks to the intake manifold into a bucket, then stuck my garden hose up to the one that attaches to the steel tube at the water pump. Flow water thru there at as high a pressure as your hose will manage until it runs nice and clean. Flushing both directions a couple times won't hurt you...... just end with reverse flow. (applying pressure to the hose that hits the water pump) When you are satisfied with that, hook the hoses back up, trying to lose as little fluid as you can manage. Then, just burp the cooling system as usual, and make sure you coolant protects down to the appropriate temp.

 

just following up: I finally removed the lil brass plug and put a sensor in it's place.. my FI has two sensors in it now- one being used, and another threaded in but with no wires connected... I took it for a spin and the temp needle moved up a touch- from running around 1/4 to running around 3/8 or so.. I don't know if this will solve this riddle or not, but I'll come back and report either way..

I kinda forgot about this until I had to clear two 1281's in two days..

by the way- instead of putting in a brand new sensor, I used the one from my old keg just to see if it is/was the sensor itself.. Of course, the only way to do this and absolutely know is to put the old sensor in the hole I put the new one in when I originally installed the thing- and move the newer sensor over to the previously capped port.. dang it.. I didn't think of this until just now.

 

interesting, i burped my hose and it took like a 1/2 gallon of coolent and i have heat now. its just the needle to the temp bothers me a bit for it ot decides to overheat.

 

fwiw, my gauge reads the same as yours sheriff, but... mine was after fixing my plenum. I blamed the gauge difference partially on the slight corosion on the sender (which came right off with some carb cleaner), and slightly cooler t-stat.

 

You could get some boiling, or close to, and dunk just the tip of the sensor in it and see if the gauge reads correctly. You could use a hot plate to keep the water near to boiling. If you have to push more of the sensor in the water than what is sticking out from the F1 to get a proper reading can you get a longer sensor with out mucking things up?

Also, take an resistance reading while cold, run engine to operating temp. If there is not at least 200 ohms of difference the sender is not reading correctly, or is defective/dirty.

 

well, damn... I ran it about thirty miles this morning, and the temperature issue remains.. I'm putting on the wide band a/f soon, and I'm wondering if running rich is to blame...

 

I hope this is the last post I have to make on this subject...

I burped the system today.. I mean, I burped the hell out of it..

I reverse flushed the heater core, and I ran it until it was clear.. I worked as fast as I could to get it back together with as little fluid loss as possible.. I fired it up with the cap off, and let it idle for every bit of an hour with the front elevated while I took a phone call.. Every few minutes I went back out to it- and about 1/2 hour into it bubbles started emerging..

Still, I let it idle..

When the efans kicked on, the level dropped- and I put pure coolant into it (to cut the pure water in the core).. it took a good half gallon before it was over with.. An hour into it (I know this because of the timer on my phone), it finally stopped dropping below the neck of the radiator when the efans kicked on, so I put the cap on it.

Another ten minutes pass, and I'm still chattering to some dame.. I walk over and squeeze the top hose to see if there is decent pressure (I needed to know my heater core hoses weren't going to blow off under pressure).. There was pressure.. No leaks..

The defrost has been on high since all of this started, and I've been minding the temp gauge closely. It's been very predictable as far as gauging when the efan kicked on, and it's (catch this) about the same as BEFORE the FI.. And, glory be to Allah, I have floggin' HOT air coming out of the vent- not luke warm, floggin' HOT..

I don't know if the issue I faced is similar to the issues you guys face, but I'm leaning toward this- the sensor probe in that manifold must have NOT been completely submerged.. there is no doubt in my mind that the engine has ran at temperatures similar to the keg, but no matter what I did with the probe it still registered cooler.. It doesn't anymore. It registers similar to the way it did before the gapper, and the temperature probe in my radiator that operates my efan controller agrees with the temp sensor/sender, and I have relative comfort that the engine isn't running hot..

synopsis: If there is ANY air in your cooling system, it's my new contention that it will find it's way to both your heater core and to the raised area where your temperature probe for your sensor/sender lives.. and read inaccurately..

if anyone has followed this thread and the things I've done, I'll also add this- I have two temp senders in my manifold now.. One is monitored, and the other is just plugging a hole.. they both agree on the temperature of the truck.. It wasn't a bad sensor/sender..