I recently replaced my radiator due to a crack it had in it, but it seems that my temps are going from a bit hot to a bit cold. It will go up a bit, then down for awhile, then up, but quickly down. I replaced the thermostat a few months ago, and am not looking forward to doing that again. I just wanted to get some advise first. I also check the water level each day and it is all teh was up. 1988 Bronco, 302, aod 115kmiles

 

Sounds like you have some air in the system yet and it still needs a good burping. Park the truck on drive up ramps or a positive incline and remove the radiator cap (while it's cold) and allow the truck to run about 20 minutes with the heater switched on. You might have to to this a second time after it cools down all the way from the first try.

 

Is there a way I can do a "burping" if my heater core is not connected? When I bought the truck it was bypassed. But that seems like what I was thinking.

 

Yes, you can burp it with the heater bypassed. If the heater hoses are now a loop, just make sure the loop isn't stuck up high where a air pocket could sit.

 

Im going to try this now. But Im not sure if it maters,but both tubes ar cut, and bypassed.

 

Then make sure the ends are as low as possible so that no air is trapped in them.

 

 

It could be signs of a head gasket starting to leak, but don't fret Are you losing any water all? When you first start up cold check your exhaust for excessive water coming out. I had the same thing going on; swinging temps, never really warming up. I have resigned my self to replacing all the gaskets on the top half of the motor but not till snow season is over. Mean while I got every thing stable with some Barrs Stop Leak, I know there are those that do not condoan its use but for trouble shooting and a temporary fix you can't beat it. Ford V8's as old as ours are well known for there ability to leak water and leak exhaust in to the coolant.Just keep an eye on it and plan for some gaskets pretty soon...

 

That sucks. Would I notice water on the ground or anything like that? Or just exhaust.

 

does it get hot enough to cause the engine damage? It shouldn't, and if it doesn't then drive it for a while and the air bubbles will work themselves out. A couple bubbles in the line won't cause the engine major damage.

 

 

That is pretty normal for having just drained and refilled with coolant. It will work itself out after driving it for a while. I was worried about mine for a while after I did my water pump and thermostat, but a few road trips and it's consistent now.

 

"That is pretty normal for having just drained and refilled with coolant".

Don't take it personal (jb1390) but I would have to disagree with the conclusion. The systems are pretty much "self venting" and should require no specially procedure or run time to get a stable temperature at the dash.

"Would I notice water on the ground or anything like that? Or just exhaust".

It depends on the engine, I have wittnessed (very recently) water peeing out between the head and block, thought for sure I had to park it till I tore it down fortunatley I didn't. That type of leak is not what is causing the temperature fluxuations though it is related. Let me explain; When these engines age and I'm not referring to wear but by the number (thousands) of thermal cycles from Cold to Hot to Cold. This can cause many of the bolts to lose there torque values. Also contributing to this is the gaskets. As the engine heats and everythig expands the gaskets are compressed to a greater degree, natually when the engine cools down they have far less pressure on them due to the contraction (shrink) of the metal. When everything is new the gaskets are resiliant and can compensate for the tiny changes, over time though they lose this ability due to chemical changes of the material. Eventually leading to very small leaks (weeping), leaks you would never notice unless you made a study out of it. However as time goes on things usually accelerate especially if the cooling system is neglected. The engine produces exhaust that is readily converted to an acid. When these (Non-condenseable) gases find there way to the cooling system (over & thru gaskets) now you have a nice little acid bath acting on the gaskets which are already old & brittle. You see where it's heading.

Back to the temperature, (background the gauge that you read on the dash is what is known as a "Thermister" (Thermal Resistor). Due to the type of material the probe is made out it has a peculiar trait; As the probes temperature increases it allows a greater electrical current to flow thru (internal resistance decreases), which is backwards of most materials. It is this change of current/voltage that is read on the dash as temperature.

Recall the exhaust gases that were finding there way over to the coolant, As a side benefit these Non-condensable gases circulating in the system can/will cause other problems;

First- Gases due not have the same "thermal conduction" properties as the coolant which means the Thermister Probe will not "read it" the same as the coolant , usually read allot less.

Second- In sufficient quanity the Non condensable gases can/will cause the water pump to cavitate, rendering it useless (made for water not gas). Due to changes in engine speed, temperature and leak rates though the pump will pump but typically "in surges".

So then about the coolant temperature "low & fluxuating..."

Does any of this make sense?

 

Those temperature gauges are unreliable for the older ford trucks (and mine was acting up). took mine out and put in a good mechanical one, and the temperature on my truck was fluctuating for a few days, now it's down to normal. For this burping procedure, wouldn't it be necessary for the thermostat to be open, preferably all the way, for the air bubbles to make their way through? It seems like you'd have to drive it to open the necessary pathway to allow the air to travel. This sounds like exactly what happened to me and others with the 7.3 idi right after changing the thermostat. Maybe something is different on these engines... check for water on the ground and around the gaskets. The exhaust making it into the engine theory-wouldn't the system be constantly venting to allow the exhaust to escape? Also, doesn't exhaust pressure-due to a blown head gasket normally blow the tubes off the engine? The only way exhaust could make it into the coolant would be to leak around the head gasket, or through a cracked head (or cylinder wall, but this is very very unlikely). It also seems to me that this is a problem for an 88 with 115000 that my 89 diesel with 166000 would be experiencing this problem to a far worse degree, because compression in a gasoline engine is nowhere near compression in the diesels. Just thoughts, please correct me if I am wrong.