Engine starts to overheat once AC is switched on

Hey guys,

I am having another issue with my truck. I just got done replacing my clutch and last rear u joint. No more clutch whine/cricket noise and drive line vibrations! However, I now think I might have an even bigger issue.

My trucks temperature gauge almost always stays above a third, but below half. The rare few times it went to half or a tiny bit above were many years ago pulling the tug boat over the Cascades range. Well, it now constantly shoots towards the red after a mile or so with the AC on. The temp gauge won't move with the AC off, but it starts to fly once I turn the AC on. Coming to a stop, giving it some gas, and turning the heater on drops it to half very quickly. But it will stay there or get higher until I stop driving. This all happens in town at speeds around 30-40mph. Have not driven above 45mph since this started happening.

The coolant level, although very dirty, has remained the same. Has been for months. The engine oil is clear on dipstick and under fill cap. No leaking coolant on the ground. No coolant smell or white smoke from exhaust. However, the coolant gurgles after I shut the truck off. The overflow container fills up and then recedes after it cools down. It still did this after replacing the radiator cap today.

I started the truck cold with the radiator cap off. After 15mins with the AC pumping the coolant started to overflow out of the radiator! No bubbles, just slowly came up and out. I slammed the cap on and watched the temp gauge. It stayed below half.. I then drove it for almost a mile, still with AC on, and it shot right up!

Please do not tell me its a head gasket... Could it maybe be my thermostat is staying closed or not letting enough fluid through and that cause the overflow and it to over heat? The top radiator hose is extremely hot after all of this. The bottom hose you can touch for a few seconds.

Sorry for the long post! Let me know what you all think.

 

first off coolant should never be dirty, there is nothing in there to get it dirty so if its dirty, its contaminated with sediments that can clog your radiator and engine as well as ruin your water pump and its not going to cool properly. that said, I doubt the coolant is your problem.

its going to be a clogged radiator most probably just by your description of dirty looking coolant.

you should still check the radiator fan clutch is working ok but step one is pull and flush your radiator in the opposite direction of normal flow to see if it can be unblocked. chances are its just some of the bottom rows clogged up but that is enough to restrict flow and cause overheating under load. when you think you have flushed all the crap out of the radiator then flush it in the normal direction of flow and see if it flows freely. now fill with fresh new coolant and test drive it

 

Thanks for the response, keakar! Yes, it definitely needs a flush. I believe the color is from rust build up. The old radiator cap had some built up on it. To be honest, i could have topped it off with regular water back when I first got it (young and dumb). I'll admit, I have sort of neglected the coolant since then (almost 10yrs ago). Not very thorough flushes since then. I usually only check how full and ignore the color. Always full.

The fan roars upon start like it always has. Longer when its cold out and about 5 seconds on a mid summers day. Seems to increase with rpm increase, too. But it could be on its way out. 231k original miles on it.

With the age of the truck (1996) I will probably replace the radiator completely. The radiator hoses as well and the thermostat. I am banking on the system being gummed up and not able to handle the added stress/heat caused by the AC running. Is that a common cause for whne this rig acts like it is? To be safe, I am having it tested for a bad head gasket this Thursday. $40 dollars that I hope tells me the gaskets are fine.

 

Yeah, replacing the radiator and thermostat should help. Sounds like the thermostat may not be working right because the needle should get up to about halfway and not move around.

All the heat the AC takes out of the cabin ends up in the condenser in front of the radiator, so having the AC on will make it that much harder for the cooling system to work.

Even if the coolant still looks good, it loses the corrosion inhibitors after a few years. In older coolants they lasted 2 years. Newer coolants claim to work for 5 years. So even if the liquid in there still cools the engine, the head and block will start corroding and eventually lead to a blown head gasket. A few months ago I replaced my badly corroded and pitted cylinder head. There was also a a fair amount of corrosion around the cylinders on the block surface.

Since you said the coolant looked dirty, I'd say flush the cooling system out with one of those cooling system flushes according to the directions. Then flush it a couple times with water, like fill with water, let it heat up to circulate, then drain and repeat. After it's coming out clean, then replace the radiator if you're going to. Fill with distilled water and coolant or use the 50/50 premixed type. You might also want to do the last flush with distilled water. Locate the engine block drain plug to drain the system better. On the 4 cylinder it's near the water outlet from the block. Not sure about the 6 cylinder.

 

Thanks for the directions and advice! If the head gaskets check out okay tomorrow then I will try to get the parts ordered. I have a long trip home very soon (2300 miles) so I will replace rather than reuse. I would rather be safe than sorry!

 

Well, head gaskets checked out okay! I do need a good flush, new thermostat, and a new clutch fan. I figured/hoped those 3 things would end up being the causes to my temp problem. Can anyone recommend a good clutch fan? I am an Amazon prime member if anyone knows of one to get off there. Thanks!

 

this one fits your truck - https://www.rockauto.com/catalog/ra...com+Search+for+HAYDEN+2671&blanktemplate=true

always compare prices but rockauto.com usually always has the best prices and very fair shipping rates

 

I didnt read all the replies but my thoughts. A complete flush could loosen up junk keeping a leak from being a leak. Also I might just change the thermostat and radiator cap. You can change the fluid without doing a cleansing flush. I don't about belts in the first gens ? Is there a single belt. Is the compressor turning normally. Is the belt slipping. Just eliminate the little shit before throwing bank at it.

 

Thanks keakar! I appreciate the responses from ya. That is pretty dang cheap compared to what can be had locally. Two options at AutoZone. $90 and $120. I am not worried about doing the t stat. I have done a few. I have never replaced a fan clutch though. It sounds like it is 8 bolts/nuts? 4 holding the clutch fan to the pulley? 4 more holding the clutch to the fan? Seems pretty simple. However, I read that the pulleys can come out of alignment? That doesn't sound good to me ha

Yeah, I am a little worried about junk loosening up too, rbishopp. I am keeping my eye on it. I think I will replace the t stat and reflush again right before I head back west. Cheap to do and it would make me feel a lot better.
There are multiple belts for the 1st gen 3.4l. I replaced my belts a few years back and maybe 30k ago. Current belts have no glazing and no cracks. None of the belts squeal. I hear my new clutch throw out bearing engage over the sound of my belts/pulleys ha

 

from what I understand its real tight and a knuckle buster, so since your flushing it anyway, pull the radiator so you have room to work and make your life easier

 

Yeah, it looks to be a tight fit. I don't have too big of hands though so that usually helps me. I am debating about replacing the radiator now. I might just flush and change the thermostat. It just depends on how bad the coolant looks coming out. Then I will go from there. I will save the fan clutch for last. It still roars on start up, but not like it used to. It also didn't roar when the temp would rise above half. Just quiet the entire time. I am assuming once the gauge had hit 3/4 the way up that it would be hot enough to roar? ha

 

Good to hear the head gaskets are OK. My point about the corrosion is you don't know if or how much corrosion you already have from not changing the coolant, so be sure you keep up with changing it on a regular basis going forward to prevent any more corrosion.

 

Yes, I will keep up on changing it from now on. Especially since I'll have access to tools, lifts, shops, ect again starting soon.

Does anyone know the torque specs for the 8 bolts when replacing the fan clutch? I think it was something like 60+ in/lbs for the ones holding it to the engine and 50+ in/lbs for the ones holding the clutch to the fan?

 

download the FSM in the sticky threads, they give you all them details and more

 

The repair manual says to hold/squeeze the belt while loosening the nuts that hold the fan clutch to the pulley, but I found that hard to do. I had to fit a closed end wrench onto the bolts, then carefully tap the wrench with a medium sized hammer. It's a tight fit with the plastic fan blades in the way, but they eventually came loose. Take it slow and don't strip the nuts and create a big problem.

When tightening, I'm not sure how anyone can apply the proper torque with a torque wrench because the fan is in the way. I replaced the nuts just so if I ever had to loosen it again the nuts would be in new conditions (not starting to strip at all).