94 massive overheating

[Jonno]

Hi all,

I haven't seen this problem described on the forum archive. The other day I happened to notice my temperature gauge was almost red lined. I put the heater to max and it dropped a bit but was still above the 'L' in NORMAL. A few hours later I put some more coolant in (the reserve was low) and started it up but within 3-4 minutes the temp was starting to rise abnormally again.

I shut it down and noticed a drip coming from what I think is a flushing kit adaptor that was put on. I tightened it and figure the coupling may have gotten a little loose with the big over heat earlier. When I tightened it, I got a face full of coolant so the system seems to have pressure.

Here's what I have checked (not with any fancy tools):
1) System seems to have good pressure
2) System has coolant
3) Rad cap fits snugly
4) No oil in coolant
5) Doesn't look like water in oil
6) Top water hose on rad is very hot so I think that means the thermostat is working, ya?
7) Fan works and is in good shape
8) Rad fins are not blocked and seem in good shape

I guess that's it. I haven't found anything on the internet or repair manuals that explain how the temperature can get so hot so fast and stay there. Please correct me if I'm wrong, but if the top rad hose is hot, the thermostat is fine, correct? There's no funny sound as if the water pump is gone but could that be the problem too?

 

[bronco_lou]

How is the lower hose, I had a truck and the hose was soft, the water pump was sucking the hose flat and stopping all water flow.

 

[Jonno]

Thanks for the reply. I was not able to test the truck today. I'll take 'er for a quick spin tomorrow and see what happens to the lower hose. If it's hot an not collapsed, that would indicate (I assume) that the coolant is flowing through the rad. I wonder if the thermometer is faulty and it's not really overheating at all?

When I last ran the engine last night, I tried it with the rad cap off to see how warm it got and it started to overflow within a few minutes so I stopped that plan.

 

[ItsA5Spd]

How hot was the upper Rad. hose? If it was too hot to hold onto for more than a few seconds, that's too hot. Could be the piece of junk gauge from factory.

 

[brendank]

I would swap out the thermostat.

 

[Jonno]

Yes, the upper hose was scorching. Plus when I first noticed the temp when driving, I turned the heater and fan to max and it felt like a hair drier in my face.

I was wondering about the thermostat but if the upper rad hose gets hot, doesn't that imply that the thermostat is opening? Also, when I start the engine with the rad cap off, the coolant starts to overflow which probably indicates the thermostat is starting to open.

However, it's a cheap part to replace so I could try it.

 

[Jonno]

Okay, now I think it might be a thermostat. I did another test run from cold. The other day I thought the thermostat was opening because the top rad hose was hot. However, today I found that it's not hot. When the engine was showing a temp in the upper normal range, where it doesn't usually get, the tube was still cool.

I shut the engine off and squeezed the upper hose and heard water flowing back through the overflow line. That hose was warm. Also the lower rad hose was warm.

Is it possible that the thermostat is not opening (either at all or very much) and the hot water I eventually see at the rad cap and top hose is just some hot fluid that naturally flowed from the lower rad hose?

I have a 4L V6 with A/C. The thermostat looks tight to get at. Anybody have an opinion on how easy it is to replace?

 

[brendank]

It just seems like a thermostat problem to me. If it was working one day, and then all of a sudden the next day it just started overheating, that screams thermostat not opening.

It's a fairly tight space, but you can do it without really taking anything else off. I work with a 1/4" rachet, some extensions, a small socket, and one of those little swivel u-joint socket adapter thingys.

Should take a 1/2hr max.

 

[Jonno]

Cool! Thanks for all the advice guys. I bought the parts so as soon as the rain stops I'll head outside and start the work. Or I'll make space in the garage to actually fit my truck inside

 

[cocoasranger]

When I was changing my thermostat I tossed the old one and the new one in a pan of water on a hot plate. The old stat only opened half way and only after the water was at a rolling boil. The new one opened quickly and was full open way before the water boiled. Not sure it proved anything, but it was fun.