ak170b

First off this is a great forum, up until this point I've always found the answer by searching threads. But now this problem has me stumped.

Truck: 91 xcab 4x4 V6 200,000 miles

Problem: Truck has always run on the hot side, just shy of red line, but produces very little heat, no heat at idle.

Resent work: Last year the front main seal went so I replaced the oil pump, water pump, timing belt, and the appropriate gaskets and seals. This fall when it got cold and I turned the heat on fogged up the window and smelled antifreeze (I knew both the rad and heater core leaked but it was tolerable until now). The radiator was boiled out and repaired and the heater core was beyond repair so replaced with new (heater core replacement instructions in the Toyota factory repair manual are lacking, but I got it done). Also, on installation I took extra caution in reassembling all ducting and valves to ensure they were working properly and sealed.

So, after assemble the temp was hotter and the heater less (burped the system made sure there were no air locks) still nothing, pulled the water pump and thermostat, tested and inspected both working fine and look fine, so reassembled and still same problem. So, pulled the hose going to the heater core, started the truck no flow increased throttle and it flowed but not very aggressively. Then drained every thing and blew air through all the different routes, seams to be no apparent restrictions to flow anywhere. I'm running out of ideas. Sorry, about the wordiness but more info is better, right?

Any ideas are appreciated, thanks Paul.

Bigblock

What about the T-stat?I'm picky about them.They're also easy to replace.Get it from the dealer.If that don't work I would pull the intake and see if the large heater pipe has a restriction.I'm sure you have already ruled out a guage or electrical problem!Do the hoses or pipes actually feel hot to the touch.Does the water valve work?Hoses will also collapse on the inside and plug.How long does it take the engine to show normal temp?Shouldn't be over 5-10 min max.You may have a restriction to the guage branch of the system(one of the small pipes branching off the main heater pipe under the intake).
Bigblock

ak170b

Ya, put in a new yota t-stat, gauges and electric are good, hoses are hot have had all of them off at some point they are good, I also drained all the antifreeze and blew through the different runs, like the heater pipe, heater core, checked the valve, and return line, all are ok. I'm thinking now there's a restriction in the water jacket some where. Looking at the cryptic coolant route drawing in the yota repair manual looks like coolant goes threw the t-stat strait to the center of the water pump (inlet) then there are two smaller water pump outlet holes that go straight in to the block (water jacket) then after circulating through there exit either to the rad or heater circuit. So, if the t-stat hasn't popped water should just circulate through the heater circuit looks like the heater return pipe dumps in to the water pump intake. After driving it today the temp is running a little hot as long as your moving but soon as you stop the heater slowly gets colder and the engine temp rises. Well, I think I'll tear it all apart again tomorrow, check out the return pipe and some of the coolant passages, a buddy has a nice video bore scope my be I can find some thing with that.

Thanks, for the input 3yotys, I'll update as thing progress.

Paul

jpmountainboy

remove the t stat and just give it an extra minute to warm up. just hammer out the guts and leave the outer ring to keep the seal in the rubber part. I got tired of mine failing and have had no problems since removing it.

TNRabbit

I've never had any issue with my truck overheating; it's got the factory radiator,j fan, & OEM thermostat. If you're overheating, something is wrong somewhere. Are you certain you're getting ALL the air out of the systtem? Park it uphill & let it run from cold to hot & add coolant/water until no more will go in.

Another thing to check is if your radiator is plugged.

jpmountainboy

when I re-did my engine I couldnt get all the air out with any of the tricks, and yes the water was not circulating because of it, so thats when I removed the guts from the thermo to get it going. I ran it with the cap off and slowly kept adding until it stopped going down. air can get caught way up in those heater hoses off the bypass and I just couldnt get it out even on a big hill with a jack under the front.

SEAIRESCUE

A soft/old lower radiator hose will collapse under power, not idle. Also, I would highly suspect the job done on the old radiator. When they leak, replace them. The T stat should be the type with the little jiggle valve in the center as it minimizes air traps in the system. There is a cable from the inside that controls the heat valve under the hood. Is that free and working properly? Most near top of rear firewall area.

My $0.02