Overheating/slow heat issue

[aran]

Arrrrg, I've searched this forum over and over with mixed results, several threads with similar issues end with no conclusion(which drives me nuts, post an update on what your resolution was!!!!).

Anyhoo, 94 FZJ80(275k miles), sat for several weeks, when I started driving it again, it starts to overheat, or reach the red, never actually overheats(I know from hours of searching that our gauges are more like a reference point), so I'm not sure how hot it is actually getting, but seeing the gauge in the red is bothersome. A seemingly corresponding issue, or maybe coincidental, is that the heat won't kick on until it is really warmed up, blows cold air then heat kicks on like normal after 6-8 minutes of driving. I'm not getting any weird, sweet coolant smells, runs like normal, coolant and oil look ok. I have a thermostat and gasket on the way today, and was just wondering if anyone had any thoughts on other possible issues? Should i just replace the stat and report back before jumping down this rabbit hole?

I'll post an actual conclusion when I get to the end of this mess for future generations consumption.

 

[Malleus]

Does it ever cool down during operation? If it does, I would lean towards the thermostat. If it doesn't, that's not the problem.

I would suggest assuming the heater problem is coincidental, and proceed form there, fixing one problem at a time. The cooling system was designed to be sufficient without the additional heater core volume, so even if it doesn't work (that is, your heater valve doesn't open properly) your engine operating temperature shouldn't be affected.

 

[aran]

Does it ever cool down during operation? If it does, I would lean towards the thermostat. If it doesn't, that's not the problem.

I would suggest assuming the heater problem is coincidental, and proceed form there, fixing one problem at a time. The cooling system was designed to be sufficient without the additional heater core volume, so even if it doesn't work (that is, your heater valve doesn't open properly) your engine operating temperature shouldn't be affected.

It does seem to cool down some, or at least the needle bounces around some, going up and down erratically for some time, eventually staying in the upper area of the gauge. I've never driven it long enough to see if it actually overheats.

I'm reading more now, and I'm going to flush the system, do t-stat and a few other PM items I've been putting off and report back this weekend. I have several oil leaks, dist o ring, oil on tcase(hoping speedo o ring, prob upper pan though), and a blown out center muffler, which I will be replacing when it arrives. I also noticed a bunch of random stuff that needs to be fixed, like purge tank line is just hanging out, o2 sensor fell out of cat(no idea when/how that happened). It's a mess right now and I need to catch up on a bunch of stuff.

 

[baselfish]

also forget not yer water pump....

indeed if you are going to break / drain h20 system - put in a t-flush and new tstat - whislt you are up in there-
might think about the water pump....

does sound like your heater core may be "clogged" as well - and that is an easy flush too - with some clr and tubing -
which may solve that issue....

tstat logically does seem like the most likely culprit - but as you have researched - it can be a vexing issue...

Bf

 

[western flyer]

It sounds like you have been searching MUD. When my FJ-60 had symptoms like yours if was a clogged radiator. A flush may not be enough. I had my rad rodded which ended the symptoms. I eventually replaced the rad.