One weird overheating problem

[AdamDude04]

95 EB with a 351W

Runs perfectly fine on hot days with A/C on. However, when the heater control goes to hot air to keep you warm in the 40-30 degree weather, you have no hot air, and you overheat.

..overheats when it's cool outside, runs fine when it's hot outside. Thermeostat running fine, and outside temps not cold enough to freeze the thermostat shut..

 

[50joe]

Um, huh. Your sure the mixture is right? The only way I could see that was if the coolant was slushing up. Even still, should thaw out once the block heats up. Damn, thats a good one. :wacko:

 

[AdamDude04]

YepYep correct mixture. Was drained less than a year ago and filled with 50/50 pre-mixture

 

[Bronc76]

Heater core? It could be blocked internally. It could explain why its not heating.

 

[bobstrat]

actually my 95, 351 started acting like that except my heat is unbelievable. i can drive with the windows down at 45 mph in 25 degree temps and am toasty. i stopped driving it, but i'll be looking into it wed. and thur. when it warms up outside. when you say overheat, is that on the gauge or is it displaying physical signs as well? my gauge started spiking hot and then cool off. top hose is warm, bottom hose is cool, yet it never physically overheats. no steam, no extra coolant in the reservoir, no funny bubbling sounds, water pump isn't leaking or making noise and it isn't losing coolant. i don't honestly know if it is really heating up, but the gauge is all over the place and it only started with the cold weather. i'm thinking i'll just replace the water pump/t-stat and drop the radiator off for a professional cleaning since i just bought it in october and don't know anything about its maintenance history.

 

[50joe]

Heater core? It could be blocked internally. It could explain why its not heating.

I was thinking that, but that doesnt explain the overheating when its cold out. Especially if its fine when its warm out. I dont get that part of it.

 

[AdamDude04]

I'm thinking of maybe when the heat is turned on, something somehow blocks the coolant flow?

It runs fine as day as long as the heat isn't on. I assume there is something that re-routes the coolant, at least some of it (enough) and that will cause it to overheat?

The upper and lower radiator hoses feel normal (hot/warm).

If the heater core is plugged..would that cause it to overheat while also providing lack of heat too?

 

[Krafty]

if the heater core is blocked then the flow of coolant would be greatly reduced, so not as much coolant would be cooling in the rad as it would if everything was flowing properly. causing the temp of the engine to climb, my truck did that once but I knew it was from ice, it heated up fast then thawed the ice and its been fine ever since. next time it does this check both heater hoses, if your not getting hot air, and one of the hoses is hot and the other is not. then you have a blocked heater core.

 

[AdamDude04]

Yep.. I checked the heater core hoses in the engine bay.. inline was hot (too hot to touch) and outline was slightly warm, not enough to keep your hands warm in 20* weather tho.

So a simple squeeze of the hose for half an hour, and reving constant at 2500rpm somewhat solved the problem. While crusing down the road, it'll blow hot air. Sitting in traffic like conditions, and go back an forth from warm to hot. But if doing a constant 55mph, hot air.

Sounds like a huge air pocket that wont come out?

 

[Krafty]

have you tried starting the truck and letting it run cold with the cap off for a minute?

 

[AdamDude04]

We did for an hour. There were constant bubbles the entire time until the very last 10 minutes..

 

[Krafty]

then you top it up and do it again

 

[92bronco_in_progress]

We did for an hour. There were constant bubbles the entire time until the very last 10 minutes..

could be air in the system.....are you losing any coolant?...by the way adam i managed to find a couple pics the truck im searching for, posted them up on the thread about it

 

[AdamDude04]

I'm thinking a small crack in the head..inducing small amounts of air into the system.

I'll check out the thread..my friends number is no longer valid..I'll try other modes to find out her new number