[2fordtrucks]

My 79 Bronco will run in the "M" range for a while and then go past the "L" and hover there for a little and then shoot back to the "R". In the NORMAL. I know it is normal to run in the normal range, but why the fluxuation? Is this a sign of a bad thermostat? Also, if you have a plugged catalytic converter, will this make the engine run hot? Thanks. Oh, it is a 351M with a 4bbl carb with no egr or air pump, dont have to have emissions for this old of a vehicle. It does still have a old cat on it though. Thanks for all your help. :shocked :slap :chili:

 

[ESC]

Check your coolant level. I've seen this with air in the system.

 

[2fordtrucks]

Thanks. I checked it yesterday, it seemed normal, but should I check it while it is running and warm?

 

[Gub_Ni]

Yes, take the radiator cap off then start the truck and wait for it to heat up. It's normal to loose some coolant, but if you loose a lot then it's air bubbles making it overflow. Fill it about 80% and continue to let it run for awhile so the themostart opens and closes and you get a total flow of the system then top it off and close the cap. Also it's fairly normal to flex on the temp, but that's too hot. Get a lower temp thermostat b4 you cook the engine.

 

[Lonestar_Bronco]

Replace your sending unit as well. My guage was doing something like that. the needle would go to the top of the range and sit there. Sometimes, the engine was still cool. I'd pop the hood and feel that the uper hose was still cool. I'l echo what GubNi said, be careful not to damage your engine.

 

[2fordtrucks]

I was going to sell the bronco after I got frustrated with it, but with this kind of help, how can I. You guys are great. I look at these forums everyday and try to help when I can. Thanks a lot.

 

[Lonestar_Bronco]

It does still have a old cat on it though.

You don't need it, do you? if you're worried about it having possibly collapsed, replace it with pipe.

 

[Gub_Ni]

You don't need it, do you? if you're worried about it having possibly collapsed, replace it with pipe.

Somebody has been drinking again! Without a thermostat in the winter the engine would never warm up and the carb would be running on choke all the time. That would mean 2 gallons to the mile, no heat, and no power. In the summer depending on where you live you might get away with it.

 

[2fordtrucks]

Somebody has been drinking again! Without a thermostat in the winter the engine would never warm up and the carb would be running on choke all the time. That would mean 2 gallons to the mile, no heat, and no power. In the summer depending on where you live you might get away with it.

I think he was talking about the cat converter. At least I hope so. lol. :beer

 

[Fixer]

Check the radiator for cloged fins,but pay atten.to the middle of the rad,if it has a viscous drive fan hub the bymetal spring wont pick up the heat until it really starts to get hot then it will kick in and cool off,and go thru the same cycle.

 

[2fordtrucks]

OK, I ran the truck with the cap off this morning and let it warm up. It ran for about 15 mins, and the temp never went above the "M" on the gauge. I could see the steam coming out of the top of the radiator but the coolant level never changed. The truck did not run hot. I put the cap back on the put it into 4 low and moved it forward and backwark just playing, hehe, and the temp went up a little but not much, and still no change in the coolant level. Oh, the level was about 2 inches below the cap.

 

[Gub_Ni]

That seems ok, could you see the coolant circulating?

 

[2fordtrucks]

no, I was looking for that, but after it warmed up all I saw was steam coming up. so some coolant had to be circulating for it to steam up.

 

[Gub_Ni]

With the coolant at that level you should see it gushing from the left into the center. I don't think you let it warm up enough or your thermostat isn't fully opening. It may take 30 min.

 

[Lonestar_Bronco]

I think he was talking about the cat converter. At least I hope so. lol. :beer

Yes, I was. You can see that by reading my entire post.

Have you checked or replaced your thermostat recently? Also, do you have antifreeze in your system? It sounds as though there was so much steam you couldn't see the coolant. This should not be the case if the temp guage is only in the "M" range.

 

[2fordtrucks]

I do not think the thermostat is operating properly. With my limited time I have, this weekend I am going to repleace it. I drove it about 10 miles this morning and it got up to the "M" range and I jumped out and checked it, no movement but some steam. I figured it should be moving where I can see it. The thing is it gets up to between the "M" and "A" and then goes back to the "O" and "R" range. Strange. I think a new sending unit is in the works to.

 

[Lonestar_Bronco]

I do not think the thermostat is operating properly. With my limited time I have, this weekend I am going to repleace it. I drove it about 10 miles this morning and it got up to the "M" range and I jumped out and checked it, no movement but some steam. I figured it should be moving where I can see it. The thing is it gets up to between the "M" and "A" and then goes back to the "O" and "R" range. Strange. I think a new sending unit is in the works to.

Sounds like a plan. Both of those parts should run you under 12 bucks. :thumbup Good luck