So when I was working on replacing my oil pan gasket a few weeks ago, I decided that since I had things apart I would go one step further and remove the radiator for a flush. No issues there.

But the steel hose that runs across the top and acts as the return line for the TB was plugged full of sludge. I mean, really, really bad. I tried clamping the rubber part of the hose onto the end of my air gun, and at 125 PSI this sludge would not budge.

So I decided to go ahead and delete the hose. I hear guys on here all the time talk about deleting it- or cutting off the TB line anyway- and I didn't see the problem. It's not like I can't get a replacement later on down the road.

Anyway, I've noticed a couple things since then, and I don't really see the TB antifreeze hose making that much of a difference but I need opinions.

First, the upper manifold only, is not as hot as the rest of the engine. Prior to the change, the upper manifold would be just as hot as the rest of the motor.

Second, it's taking longer for the motor to warm up.

Just curious if the TB hose delete has something to do with it or if there's something else I need to be looking at.

 

The TB gets a steady supply of engine "coolant" all the time with this hose in place and when the engine is at operating temp that means this fluid does more heating of the intake than cooling. You would think that is bad but the fact is this helps get the engine up to operating temp faster and also helps maintain it at that temp and this improves fuel efficiency. This supply of hot fluid is also nearly manditory in cold weather conditions to prevent throttlebody freezing.

On this vintage motor the location of the engine air temp sensor in one of the front intake runners also plays a part in how the EFI computer is programmed to go into closed loop. Because of this sensor location and the presence of coolant in the TB air temps are higher and more uniform than ambient temps.. usually in the 130-160deg F range. On later trucks this sensor was moved to the air box and as a result the computer will be programmed differently than it was for the early trucks, and I suspect removing the TB coolant lines has less negative effect on these later models.

 

Alright, thanks. I'll work on getting a replacement line then. Hard to believe that such a small hose makes such a big difference.

 

***UPDATE***

Okay, so I got a new line running from the TB to the neck of the radiator this morning. I had some errands to run so I figured what better way to see how its operating.

It's still running cold.

I let it warm up for probably 5 minutes before I took it out [its getting cold in this part of the country], had a few minutes of in town driving before I had it on the interstate. 20 minute drive at 60 mph- the needle didn't even move past "C." But I thought, maybe, just maybe, it's possible that my temp sensor went bad, so I'd just watch it and see what happens.

Got to my first destination, parked it for maybe 1/2 hr, then drove it more on the interstate. About another 15 minutes at 65 mph- needle still didn't move past "C."

Hit up my 2nd destination, parked it for about 10 minutes, then when I first got in it and fired it up, I was letting it idle for a minute as I was trying to respond to a stupid text message [I HATE 'EM! ] and I noticed the needle moved just barely past "C." But then as I headed home, the needle fell back below "C."

My guess is the thermostat is stuck open- I don't know what else it could be. Prior to removing the line the engine would get up to temp within 10-15 minutes depending on how soon I started driving it; and now that the line is replaced it's running cold. I don't know what else it could be. I know it's running cold because several times I checked the temperature of the heat and it was luke warm at best.

But, and this might be unrelated, but I used to be able to hear coolant dumping into the heater core after startup and the thermostat opened for the first time. I can't say for sure when it quit doing that because I honestly wasn't paying attention, but I did notice on todays drive, I didn't hear that. Is it possible the heater core is partially or fully clogged?

Thanks again- you guys !!!!

 

bump! bumpity! bump bump!

 

hows your heat? My 88 5.0 did the same thing. and it was the temp sensor

 

Like I said, I think it's a stuck t-stat, I'm just looking for confirmation.

 

Gonna ask the stupid question, someone's gotta might as well be me, are you sure its full of coolant?

Low coolant would have the same exact effect.

If its full, you know it is then yea time for a new T stat.

 

Well I just got home from work so I can't check it now but I will before I go to work tonight.

I guess I figured if it was low it would be running hotter.

I'll let you know.

 

The dash temp gauges on these trucks always read low, but the motor should maintain temp after warming up if the thermostat is working properly, so it sounds like yours may not be. I replaced the dash gauge temp sender on my 5.0 with one from a parts store and my gauge now stays around the middle or straight up, I know the engine temp is normal so I guess this sender is calibrated a little differently.

Note that not getting enough heat in the cab is almost always due to a a clogged heater core or blocked diverter door inside the blower box and is often unaffected by the t-stat operation once the motor is at operating temp.

 

Understandable, but I find it hard to believe that the needle would be reading below "C" even if the gauge is reading low. Plus, as I said, I did notice that when at a stop light or just idling, the needle would rise some and then drop back down as soon as I put the truck in motion again. This tells me the engine is trying to build heat but it's not working.

I'm aware of that, and it's possible that's the problem with mine because, like I said, I can usually hear coolant filling it every time it's run. But even assuming the heater core has been partially clogged for a while, say even before I removed the TB line, I never had a problem with getting good, hot air into the cab.

Also, danr1, I checked the coolant level a little bit ago, and it was less than 1 quart low, so that's not it either.

To suddenly have the engine running cold and not get hot air into the cab when neither one has been a problem before points to a stuck open t-stat, so that's what I'm going to check first. I was just looking for 2nd opinions and now, if that doesn't turn out to be the problem, I'll know what else to look for.

Thanks again guys.

 

I have never had the throttle body ever freeze on any of the cars i removed the tb heater on. Got a bit of performance outa them too. if your getting low heat or it takes forever to get heat in the cab it is probably a stuck open stat,but ive seen them stick more closed than open. Ive had trouble venting the air from the system on my truck bout every time i drained the coolant, so i'd double check the level in the radiator. If you change the stat make sure you use a dab of silicone to hold the stat in to put the neck on.

 

I've been having similar problems with my 96 5.8. Heater not getting hot and temp guage reading at about the N.(it used to read at the O-R) I've change the t stat 4 times with no improvement. I had a lazer temp guage on the block reading about 180. Have been told to back flush the heater core and maybe the temp sending unit may need replacement.

 

Stuck open t-stat indeed.

I got it changed today. I'd forgotten that last time I bought one I bought a "fail safe" stat from Murray products. If you're not familiar with them, if they fail then they stick open to prevent overheating. Most certainly what happened. I'd guess between that and the winter cold the engine was running really low.

Thanks again for the advice.