tpluttig

Greetings all,
I've got a real "bean scratcher" of a situation I could use some help with.

I recently had some mechanical difficulties with my '94 4-cyl. pickup (4WD,MTX). I lost the drive belt for the alt./water pump. I managed to get it limped back home but it was overheating pretty badly as one can imagine. Thank God it was only about 10 degrees outside! It also appeared that I drove it far enough to fry the battery as well but that's another story.

So here's my question/dilemma...
I got a new belt on it. At first, it ran hot to the point of overheating & I wasn't getting any heat in the cab. I let it cool down & checked the fluid level & bled the system. Then the engine temperature gauge was reading a little on the hot side but within limits & I had heat inside. Then, it started running really hot again but I still had heat. So I picked up a new thermostat thinking the other one got cooked. I took it out again today for a test ride to see what it would do and now it seems to be running a little under temperature but with plenty of heat inside.

I have to admit the I'm not much of a mechanic. One thing that seems strange to though is that the lower rad hose isn't getting hot. Is this the way it should be or do I have something else going on here? I guess I thought the hose would be almost as hot as the upper. One other oddity I noticed is that the control lever for selecting fresh air or recirculating doesn't seem to work any more either. Any possiblities that these are related? I don't know if the sensor got smoked & that's why it's all over the place? Is there a way to check the coolant temp sensor?

If anyone has a suggestion on where to look or I should be concerned about larger problems, please do let me know. If there's one thing in life I have a hard time dealing with, it automobile problems. Thanks in advance.

jadcock

The lower hose is the supply to the engine and the upper hose returns the hot coolant to the radiator. The coolant filters down through the radiator, theoretically losing a LOT of heat in the process, and returns to the engine through the lower hose, obviously via pressure from the water pump. This hose will naturally be much cooler than the upper hose. I never really thought about how hot it should be...cool to the tough, or just warm, etc. If your temperature is steady according to the gauge and you're still getting heat, it sounds like you escaped irrepairable damage to your engine. Good move changing the thermostat!

By the way, the initial overheat situation after you got the belt back on was probably caused by a large air bubble in the system...I bet the coolant wasn't really boiling. The gauge was probably reading the real hot air in the bubble. The heater core may also have been dry...which is why you initially had no heat. Sounds like everything is back to normal there.

How do you know the fresh/recirc selector isn't working? Do you hear no change in the "tone" of the fan. You can usually hear the HVAC system get somewhat "louder" when in recirc mode. You can also usually hear a mechanical "thunk" as the door switches from one position to the other. On my truck, it's pretty noticeable. I seriously doubt, if it really is malfunctioning, that it was caused by the engine overheat.

__________________
Jason Adcock
Always Tread Lightly!
1995 4x4 XE King Cab - 189,000 miles
1997 Cadillac Seville - 141,000 miles

Bror Jace

Many modern cooling systems, with their circuitous routing are notoriously difficult to bleed and require running with heat and A/C on while bleeding in a certain sequence, depending on model.

One thing you might want to consider doing is a used motor oil analysis to check the soundness of the headgasket after the (possible) overheat. It'll be about $20 depending where you go. I use these guys:

http://www.blackstone-labs.com/

Even traces of coolant will show up ... and cause accelerated wear, especially in the main bearings.

__________________
--- Bror Jace

tpluttig

Thanks for the information & advise. I will look into the link to get my oil tested. Hopefully I didn't muck the thing up!

To clarify my situation a little bit, I actually have not changed the thermostat yet. When I took it out for the last 'test', that's when it seemed to running at around it's normal temp. Plus I've run it now a couple times for more extended periods & it seems fine. Maybe I shouldn't be worried but it just seemed wierd to a novice like myself. I guess I had thought the lower hose would/should be warmer than it was, but again, I'm a novice.

As for the control lever problem, mine used to make the big 'thunk' when I would switch between them plus there was a fair amount of resistance in the lever itself. Now there's no noise & the lever just flips back & forth. I'll have to look into what's going on behind there. Please note that I do have a Chilton's manualto refer to also. But to be honest, I'm starting to develop a rather negative opinon of it. It doesn't even make mention of where the dumb thermostat is located & how to get to it to replace it. If somebody knows of an "Auto Repair for Dummies" book out there let me know. I think I would know what my limits of talent were if I had a decent reference.

But I digress. Thanks again for the tips. this is a great place to look for help!

tp

jadcock

That does sound like the recirc lever got disloged from the control arm for some reason...meaning the lever you control obviously isn't moving the door anymore. I believe you'll need to remove the front panel and radio to get to the rear of the HVAC controls, but I'm not certain. I hope someone else can help you out here.

__________________
Jason Adcock
Always Tread Lightly!
1995 4x4 XE King Cab - 189,000 miles
1997 Cadillac Seville - 141,000 miles