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Discussion Starter #1
About a week ago my 1990 RRC which normally reads quite low for temp suddenly shot up to 1/2 way within a few seconds after first warming up for a few minutes and driving half a mile. The temp rise was almost instantaneous. Seemed odd, about a mile later I get a leak from my lower hose which has been intermittently leaking for a week every few months this past year. Was bad enough, and instant enough to spray coolant on the belts and get the alt belt squeaking for a min. Pulled over, leak stopped and temp returned to a 1/3. Now half the time during the past week the temp gauge will shoot up to halfway usually during the end of my commute one way or the other and I will usually spring a leak in the same hose in the same spot which will almost always stop within a min and the temp will stabalize.
I was thinking Head gasket could be cause of heat and pressure increase cause they do go hand in hand on this particular problem. It just seems weird that the temp will rise so suddenly and stop at about halfway(usually). Ive had one longer trip(about 40 min) much higher speed where I pushed it a bit just to see if I could trigger the problem. Temp stayed real low the whole time and didnt do anything wierd at all. Once i pulled in to the driveway at my destination it sat idling for a min and suddenly temp shot up to halfway out of nowhere and it sprung the leak again. Topped off coolant, restarted a min later and all was fine, temp at 1/3 no problems, no leaks.
In my particular situation, I try to pull over now whenever possible as soon as I see it do its wierd rising temp thing to check for things under the hood and ive noticed the upper hose is usually at a reasonable pressure but the lower one is usually pretty hard at that point.

I have NO other signs of a head gasket leak, No coolant in oil, no white smoke, nothing.

So somewhere I have a big buildup of pressure between the lower radiator outlet and the water pump. And whatever is causing that is most likely the cause of my temp issues. Really that is the big question here which I think will be the answer to my problems. Either some blockage in the engine, head gasket sending pressure and heat the wrong way, water pump not working correctly?

Gonna change my thermostat now and top off. Also I did notice that my fan clutch seems a little weak so I'll be replacing that next. So basically don't know if problem is excess heat causing pressure or loss of pressure causing heat, or heat and pressure coutesy of the head gasket.
And by the way, It has been single digits to teens here all this whole time, Problem started about when it got real cold.
 

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Ok, Replaced the thermostat in 10 degree weather. Not much fun but not really a tough job and my engine was still a tad bit warm so that helped to make it bearable.
Refilled the coolant and started it up, warmed up pretty much how a normal vehicle would instead of the usual running cold situation.
Let it idle for at least 7-8 minutes, Once the thermostat opened the temp went up to just under halfway at a normal pace.
Let it run like that for 5 min, upper and lower hose have a normal pressure, 5-10 psi, both of them warm.
Took it for a 10 min drive and temp never went past halfway and lower hose did not seem to be building up tons of pressure like it was.
Carpooling tomorrow but will have a longish ride on sunday to see what it does.

I'm not getting my hopes up, but it seems like it may have helped at least, Please post a reply if any of you have any thoughts or suggestions.

I tested the fan clutch and it does seem fine after all, after getting hot it turned freely with engine off but I realize now that if it sits in the heat for 20-30 seconds it does start to do what it is supposed to, So I guess when i checked it before it was pretty cold just due to the outside temperature.

Also I tested the old thermostat in pot of water, It starts to open at about 160 degrees F. and is fully open at about 200 degrees F. Does that seem normal?
 

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And yeah I have anti-freeze in there but to be honest, I should have had a higher ratio cause the mix was a little weak. It never froze but i bet it came close. This past summer I got into the habit of just adding water every time it decided to leak and I switched to adding straight antifreeze around oct but I didnt really have any reason to add anything in a while cause it hadnt been leaking.
 

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Discussion Starter #5
Update, New thermostat seems to be functioning exactly as it should but still have same leaking/pressure problems. Instead of the up and down temps everything has seemed to level out. Starts cold, 5 plus mins later thermostat opens and temp rises fairly quickly to halfway and stays there pretty solidly. Problem is lower hose still leaks usually after I finish my drive or towards the end. Could be normal pressure causing existing leak to spray out or could still possibly be pressure from leaking head gasket. Either way I do feel better so far knowing that the temp seems to be stable while running and not rising dramatically for any reason. Next step will be either replacing bottom hose and see what pops next and/or having coolant checked for signs of combustion gas/hydrocarbons. Will keep everyone posted for the benefit of future readers with similar problems. Any suggestions/ tips are highly appreciated, Thanks!
 

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Coming out the lower hose where it joins the rad? You need to seal that leak first and foremost and then see if you are still losing coolant/temp/pressure problems.

Have you been mixing coolant types?
 

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Discussion Starter #7
Thanks for the reply Rufant,
I don't always buy the same brand of coolant since it always leaks fairly regularly but its usually prestone, always green and always ethylene glycol based. Although PG is prob better for an aluminum engine (at least according to VW).

Just ordered a lower hose from atlantic british and shoud have it wed. Great prices there by the way.

Still no overheating, just leaking every trip from pin hole in lower hose, up high by the water pump. Hopefully it is just leaking at normal pressure. I guess you are right, I won't get anywhere by guessing and I just have to replace that hose that I know is leaking before I can really make any accurate diagnosis of the cooling system. Should have hose installed thurs morning and will update after that. Thanks again!
 

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Ok, I replaced the Lower radiator hose on christmas eve. I flushed the system with water about 5 times before filling with new coolant at about a 60% coolant, 40% water mix. Everything pretty clean, radiator has good flow, no contamination visable in coolant. Changed oil right after that and absolutely No water in oil whatsoever.

Lower hose had a hole big enough to jam a screwdriver through, it went in at an angle so it must have been sealing itself from time to time! No more leaks, no insane pressure buildups like I thought.

I guess what happened was the coolant once under enough pressure was spraying out causing a lack of flow, drop in pressure, and was spraying directly on the fan belt up high at the water pump! Those combined explain my near overheat symptoms. I wouldnt be surprised if it was causing the water pump belt to slip too. I never noticed any belt slippage until it was bad enough to get the alternator belt to slip. I always knew the leak was there but could never find it because the belts would soak the whole engine compartment making it impossible to spot the source of the leak.

Truck is now warming up perfect, cooling itself perfectly, and warming the interior exactly as it should with no leaks at all! So I guess I got lucky this time, will keep my fingers crossed and if I hadnt caught this problem I'm sure I would have fried the head gasket.
Thanks for the advice guys, and good luck to future roverers reading this post!
 
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