QuestionQUESTION: Hello, I have an 88 GMC Jimmy (full size) with a 350, auto w/OD and A/C. On warm days my heater blows very hot air and on cool days it is lukewarm. I have changed everything from a water pump, t-stat, fan clutch, new radiator, hoses, everything but a heater core. I ran water from a garden hose through the core and got water out the other tube, couldn't tell how much water because it would come out both tubes (not a good seal with a nozzle). My heater box under the dash gets hot when it's working right and all hoses seem to be equal temp. I notice my temp gauge will go a little over 210 and drop back to maybe 190 and back to 210 a lot. Usually when driving at highway speeds the gauge reads 210 and when I come to a light and stop it goes down to 190 or so. I can't find a heater control valve, should it have one? The parts store shows one. I can hear a hissing sound when I slide the control from floor to vent and so on. And I hear the door move with sliding the cold/hot control. The coolant is full and new (50/50 mix). Thanks for your time.
ANSWER: Bobby;
Hi well it sounds like you have a leak or air in the cooling system .you should do a pressure test on it. also have you changed the thermostat.I would check the pressure first.
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QUESTION: Hello, I finally got to do a pressure test and found my bottom heater hose at the firewall (the one going to the back of the intake) started to leak. Now, will that cause the truck to suck in air to the system? I'm not sure if my heater core or heater hose is leaking. It never leaked under normal running. It came out with a constant drip. The clamp is tight. Thanks
ANSWER: Bobby;
Hi well if you are not holding pressure it will cause all types of cooling system troubles.no-heat, too much heat-over heat. if I were you- I would tighten or replace the hose, than go and get a can of BARRS STOP LEAK- add it to the rad. and follow the directions on the can. it might just stop the leak if you have a small one. And for less than 5.00 it is worth the try. ok
let me know how you make out. GOOD LUCK !
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QUESTION: Hi, It is NOT holding pressure!! I left the gauge on the system for an hour to an hour and a half. It went from 16 and right now it is at 9 psi. So would that make my temp gauge fluctuate? I do get very hot heat and the next time I start the truck it might be cool heat. Plus, my temp gauge might stay right at 210, and then when I pull into my driveway it sometimes goes down to 190. Do you think that this is all related to not holding pressure? Thanks again for the quick response. You will definitly get a good feedback from me.
ANSWER: Bobby;
Hi well you have a leak and with a leak you will have no presshure and no heat or very little and yes the gauge will fluxuate. try the stop leak and check the end of that hose to see if it has a crack but do not twist it off the heater core cut it on the side with a razor and get it off that way than remove a inch or so and put it back on or replace it and try it.
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QUESTION: Hi Roger, You helped me last time so I have other questions. It has to do with a ported vacuum switch. Where exactly does it go, in the water outlet? My 88 Jimmy 350 calls for a 4 port one. The ports are marked as follows, 1,2, HV, M. What would these markings mean? Is the HV for the heater valve? What about the rest? And, where does the heater valve go? Is it inline (heater hose) under the hood? It wouldn't be under the dash would it? Does it even need one? Thanks for your help.
AnswerBobby; Hi - well one hose is in hv than to the heater, than from heater return than back to water pump. ok
I do not have a picture of it, but if you went to the library and looked in a tech book it should have a picture that you can copy. ok or a book store to get the idea.
