low temp reading

[Slooptin]

took the truck out today (89 c30 454 700r4) and got it up to speed but the temp gauge never got above the mark between 100 and 210. Is this normal or is it a problem with the temp gauge/thermometer?

 

[1987 GMC Jimmy]

took the truck out today (89 c30 454 700r4) and got it up to speed but the temp gauge never got above the mark between 100 and 210. Is this normal or is it a problem with the temp gauge/thermometer?

Go to Harbor Freight and get you a little non-contact thermometer, point it at the side of the cylinder head close to where the sender threads in, and see what you're getting at full warm up before you proceed any further. Ideally, you should get close to 195*F if you have the correct thermostat, but if it's actually running 120-135*F, your thermostat maybe sticking open. If it runs at the correct temperature, you're more than likely looking at a problem in the green wire that goes to the gauge, or your sending unit is bad.

 

[chengny]

took the truck out today (89 c30 454 700r4) and got it up to speed but the temp gauge never got above the mark between 100 and 210. Is this normal or is it a problem with the temp gauge/thermometer?

Couple of thoughts:

1. That mark would represent 155 F. 155 isn't normal but it isn't really that far off.

2. How did you seal the sender threads? The sender is ground path is through it's body and then into the head/manifold? (I don't know a lot about BB's). Excessive teflon tape application will raise the resistance to ground and the cause skewed (low) readings at the dash indicator.

3. Check that there is no coolant flowing around the t-stat. By that I mean at the outer edges - rather than through the valve disc as designed. If the water outlet is sealed to the manifold with a gasket that is too thick, there is no clamping action on the t-stat flange. Then the body of the t-stat is free to rise slightly due to the pressure/flow of the coolant under it. Coolant is allowed to flow out of the engine prematurely (before reaching operating temp) and then the problem is made worse because it is cooled even further as it transits the radiator.

 

[Slooptin]

well, I changed the temp sensor in the cylinder head with a new one and problem solved!
Although now, I'm seeing that it is overheating after i drive it around, especially in stop and go traffic. Anyone have any ideas as to the cause before I start running through a laundry list of potential culprits?

 

[1987 GMC Jimmy]

well, I changed the temp sensor in the cylinder head with a new one and problem solved!
Although now, I'm seeing that it is overheating after i drive it around, especially in stop and go traffic. Anyone have any ideas as to the cause before I start running through a laundry list of potential culprits?

I'd say you probably need to replace your fan clutch because it gets hot when you stop and all that ambient air isn't whooshing in. Especially if it's a thermal clutch, which I'm assuming it is. You can get it for cheap online. One of the first things I did when I got both of mine was to flush the cooling system. A flush kit is three dollars at Walmart and a very good investment. Even in a clean looking radiator, all kinds of dirt and goop came out. If that doesn't get you in the ballpark, I'd throw a new thermostat on there, and if still not cooling good enough the water pump. All of these pieces are super cheap and good preventative maintenance. Also, make sure you don't have any leaks, you have a good radiator cap, and there's no air in the system.

 

[chengny]

well, I changed the temp sensor in the cylinder head with a new one and problem solved!
Although now, I'm seeing that it is overheating after i drive it around, especially in stop and go traffic. Anyone have any ideas as to the cause before I start running through a laundry list of potential culprits?

What symptoms are you seeing - that would lead you to believe the engine is overheating? Are you relying on the dash indicator? If so what does it read when at the highest point? When it reaches that peak temp, does it stabilize there - and kind of move up/down just a bit?

The temp gauge of an overheating engine will peg out full high and stay there. Then the radiator cap will pop, coolant will blast into the recovery tank and steam will come out everywhere from under the hood.

A good simple test is to pull the t-stat and watch the gauge while driving around. The engine should run cool - indicated temp shouldn't even reach normal (it will probably hang around 120). If that is what you see, try a new t-stat.