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Overheating problems 81 ford 4.9
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heinz57
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Aug 8, 2014, 5:30 PM
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Overheating problems 81 ford 4.9
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 All of you have been a big help to me in the past and I really appreciate it. I'am back with the same vehicle, 1981 Ford F-350 auto, 4.9 inline 6. BHG from overheating (long story) and replaced it and it is still overheating. Did block test, compression test, no milky oil, no smoke at tail pipe, not losing coolant, idles fine, no leaks, burped radiator, have set timing by vacuum gauge (17IN/Hg Denver at 5,000 + feet).
Replaced water pump, cap, thermostat, all hoses and flushed radiator. It will idle all day long and not overheat. Drove it today early AM and it did not overheat. Drove back PM 85-90 degrees and and overheated in about 10 miles. I have probably missed a few things and that's why I'am here. I cannot figure out this POS.
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Discretesignals
Ultimate Carjunky
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Aug 8, 2014, 5:59 PM
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Re: Overheating problems 81 ford 4.9
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You check the radiator for blockages? Flushing a radiator with a water hose might not be good enough because the radiator is a parallel flow type heat exchanger. That means you might have some tubes plugged up, but the water can flow through the non plugged up tubes. Plugged tubes will reduce the capacity of the radiator to dissipate heat, especially when it is hot outside and the engine is under load.
It is also possible that poor performance from a poor performing radiator caused the head gasket to blow. Something to think about.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Aug 8, 2014, 6:08 PM)
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Tom Greenleaf
Ultimate Carjunky
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Aug 9, 2014, 3:29 AM
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Re: Overheating problems 81 ford 4.9
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Lived "mile high" for about a year. YOU HAVE LESS DENSE AIR at altitude so heat exchange must be tip top. Try Idaho Springs @ 7,500 ft. elevation and worse again!
Those are reasons to add cooling ability to new OE never mind old now and may need to even boost it more depending on use and load you may put on it. Again - expect 20+ % less capable air to exchange heat at 5,000 ft. elevation give or take,
T
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heinz57
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Aug 9, 2014, 7:31 AM
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Re: Overheating problems 81 ford 4.9
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Thanks for the quick reply. First I ran Prestone flush thru the radiator while in vehice then I removed the radiator and soaked it in CLR overnight, flushed with water and reinstalled. Could find no evidence of blockage. With cap off I can see good flow thru radiator core. Could a blocked heatercore cause the overheat? Have not checked it. Listed timing only to show that I could eliminate it as a cause. Have checked with local mechanics and 17 IN/Hg is pretty normal for this altitude.
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Tom Greenleaf
Ultimate Carjunky
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Aug 9, 2014, 8:31 AM
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Re: Overheating problems 81 ford 4.9
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Forget the Hg # as that's a number a mechanic would expect for manifold vacuum not really the point. We live in pressure but don't think that way - just take my word for it.
So you have less air pressure than sea level as said ~20% (guess) such that you need all the cooling ability up to par more than a vehicle at lower altitudes. The air flowing over radiator is less "thick" if you will so can't or doesn't have the same ability to cool the radiator but enough still for normal things even just plain breathing it only a problem with a health issue really.
OK - this is an in-line six which by nature each cylinder has at least two sides near air and end cylinders have three so just that helps by design. BUT! Water pump is in the front and the back cylinder is 6 cylinders away from it and the idea is mix all the coolant inside engine to be about the same. Hence it's designed such the water pump (about all on anything) is always pumping whether going some coolant to radiator or mixing inside engine from cold right on up to properly warmed up. Ability for radiator cap on this to hold pressure is now more important than ever. Note you must see cooking times for high altitude as water boils at a lower temp some per each 1,000 ft. so not as hot but boiling.
Looked for parts to see how this engine for a truck mixes coolant and came up short of dependable info. With that I dare say the heater core is likely taking coolant from front near water pump (warm) and returns thru back as a by-pass and mixes coolant. In that long an engine it could boil in the rear and be fine up front till a boil over and if it isn't holding pressure could be quite quickly in warmer weather added too.
Heater should work and if it does blow hot or both hoses at least warm when off it's flowing but no harm IMO if flushing it back and forth for flow also and should really.
This just needs more things to be good then lower altitude that's all. Fan clutch warm engine shut off should NOT coast by hand easily or much at all. Many are inadequate. As thermostat opens and warm air flows thru radiator this clutch should be type that senses the warmer air to hot and pull hard and you should about hear, feel the flow being aggressive vs right after a cold start up and when oils in those calm down near free wheel if colder as they aren't needed to work much.
* System must hold pressure regulated by radiator cap on this. That's just expansion of coolant and each lb. of pressure raises boiling point 3 degrees F. and keeps coolant liquid not boiling or vapor which doesn't transfer heat if that occurs inside and unseen even at rear first possible on this design.
* Radiator flow you saw is good but truth is if you see that it's not full! It should be so full it about spills and recovery bottle take the extra and returns it with range of temps, expansion and contraction or warming and cooling down. It matters big time! If never full at radiator there's a problem. Fill it. Warm up till top radiator hose gets warm, shut down, wait till no pressure felt on upper hose and fill again if opened or drained for any reason till it stays full. If not say so and we can chase down why not from simple to other problems unknown right now but already since you saw the flow it wasn't full so for that moment not good if it stays that way.
* Notes: Do NOT overuse antifreeze! + ? You need it but too much doesn't transfer heat well. Generally 50/50 mix and should measure close to protection of -34F or so.
* This and older vehicles should or would have come if place of destination was Denver (perhaps whole state) have had high altitude emissions and just maybe extra cooling as in more fins in OE radiator. You could ask for better ones for replacements for anywhere on trucks especially. If you can still read it, a sticker should say it meets high altitude specs but mostly for emissions.
In short to check or do: Heater core know to flow as intended. Coolant that stays full at radiator. Fan clutch known working and pulling plenty of air when warmed up and warm outside. Add that temp gauge on this layout should set at one spot when warmed up and not change unless long run into and higher into mountains, trailer or load but still stay close if all was well.
Last: Not being full if you left it that way isn't a great sign and could be easy or could be head gasket not staying tight as I'm near sure the head bolts on this exact engine were known to stretch and are not reusable if removed. Don't worry yet until this issue doesn't show up and system will not stay full as already said,
T
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Discretesignals
Ultimate Carjunky
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Aug 9, 2014, 9:49 AM
Post #6 of 14
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Re: Overheating problems 81 ford 4.9
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You won't be able to see clogged tubes at the lower half of the radiator looking through the radiator fill neck. The only way it to see down there is by pulling the side tanks off. You might see flow, but it might be only at the top half of the radiator. All the corrosion and junk settles to the bottom as in the pic below of a partially clogged up radiator.
If you have a radiator shop in your area, have them rod it out and test it for leaks. You won't be wasting your money and saving your engine by having it checked out anyway.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Aug 9, 2014, 9:56 AM)
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Tom Greenleaf
Ultimate Carjunky
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Aug 9, 2014, 10:53 AM
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Re: Overheating problems 81 ford 4.9
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True of course DS - you won't see that. In my area the good old radiator shops are about done and long time ago just sold you a whole new one for fixing an old one especially ones with plastic end tanks but OP check on that in your area and price it out.
Those shops could acid the whole thing well and know it was good if fixed and sold new where I am,
T
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heinz57
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Aug 9, 2014, 5:08 PM
Post #8 of 14
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Re: Overheating problems 81 ford 4.9
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OK I did as you asked ran engine ater filling to top, made sure overflow was 1/2 full, let cool down and radiator was still full. Never ran it unless it was filled up. Currently running only water due to over heat. Did once pull t-stat once and ran w/o for short time and still overheated. Heater hoses both are hot. Heater blows hot air. 81 does not have fan clutch. Truck was bulit in Canada to meet CA emissions standards at that time. Radiator is oversized for the F-350 with auto. Re-did the block test and nothing leaking into cooling system. Compression was 119-121 on all cylinders. New water pump and new v-belt. Wondering if maybe I have wrong belt? Going to check this. Bought this van in 1997 and it has always run a little hot. Easy to vapor lock and finally added electric fuel pump and it has helped over come that problem, but never has it overheated like this. The time it blew the HG the front pulley on the cam came off and I thought the alternator went bad and paid no attention to the heat gauge untill I got to the garage and it exploded in steam vapors. So it was not the radiator that caused the BHG.
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Tom Greenleaf
Ultimate Carjunky
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Aug 9, 2014, 5:48 PM
Post #10 of 14
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Re: Overheating problems 81 ford 4.9
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? Comments and questions mostly:
*Never run just water unless to make it another exit to deal with. Needs some antifreeze ASAP.
* Never take out thermostat, this engine more than most! The larger hole pump will just cool front and back overheats but satisfy gauge but boiling anywhere it's overheating. Thermostat wide open allows water pump to continue mixing coolant temp inside but not when missing.
* Seems time to just take radiator out to a shop for fix or replacement in the cards.
* Why no fan clutch? Just a fixed fan or is it electric? Has to have a good fan no matter how done. If this is ordered new w no A/C might be a fixed fan or was that way. It's been altered some if only fuel pump and hope that was well thought out such that it will shut off in a collision for example.
* It's not really as underpowered as some. 1981 was a bad smog year, Calif. emissions now in high altitude makes it worse if new and for the sake of lower emissions power took a hit on most everything.
Overall it should be a good serviceable engine. Overheats never good and less likely to blow head gasket than many but the long engine wants to be same temp (any do) more than others. Should have HD components available for plenty of things for cooling especially.
Hey - what was OE at the age almost isn't trustworthy now as seems things have been changed.
Whatever your block test is for a head gasket could have failed and don't rule it out so fast.
THE RADIATOR MUST HOLD PRESSURE AND MUST STAY FULL HOT OR COLD - ALWAYS. Close guesses are that thermostat was a 192F OE and should be and pressure cap 15-16lb rated and they can be tested too. If dirty they can allow pressure, coolant out to reservoir but not suck overflow back or if plain failed. Cheap enough to toss for good new and don't cheap out as a good Stant isn't that expensive if you don't think it's right. Hose to recovery bottle is cheap too and can cause problems with finding low coolant at radiator so toss that too if not sure - dirt cheap but use real clamps if cheap now being careful of necks at radiator and tank.
It was made to work all around even for where it is. When is doesn't something is less than adequate that all. For extremes like hauling or always heavy loads altering or adding items fine for anywhere.
Be good to this thing as it could last some good time in 'Rado (CO) as if like when I was there cars didn't rust as salt wasn't allowed on roads!
Tom
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heinz57
User
Aug 10, 2014, 8:51 AM
Post #12 of 14
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Re: Overheating problems 81 ford 4.9
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Try to answer some ? Yes did wet test on cylinders and no increase in compression. Used block tester kit (OEM Block Tester) from Autozone the first time and to double check used one fron Orielly's loaner tool program. (blockchek.com) Fluid did not change color and to check this I put it under exhaust and it immediately changed color. (Blue to Yellow)
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Tom Greenleaf
Ultimate Carjunky
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Aug 10, 2014, 9:11 AM
Post #13 of 14
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Re: Overheating problems 81 ford 4.9
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No increase with "wet" compression test vs dry! Something didn't work right for that test IMO for an 1981 especially.
Hey - it's overheating suggesting it can't transfer enough heat for a reason you have to find - duh, such is why you would come to a place like this and even get assorted ideas.
Well, here's another. If no condenser in this check by feel the temp of the radiator by hand engine just shut down. Harder from engine side but try the same as best you can around shrouding. You may feel cold spots suggesting blocked tubes for any reason. Should be tube and fin one side to the other and hose in warm to cooler out as you go over and down. If already some HE design the flow can go like a maze but doubt it on this. This one with tanks off which you really shouldn't do you could see all the way thru,
T
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Hammer Time
Ultimate Carjunky
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Aug 10, 2014, 9:59 AM
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Re: Overheating problems 81 ford 4.9
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You can take those blue fluid block testers and pour them into the toilet for all they are worth. They are not reliable at all.
I've been diagnosing overheating problems and blown head gaskets for many, many years and have had many known head gasket problems that never showed up with those foolish testers. There is only one reliable test for a head gasket and that is using an exhaust analyzer to sniff for hydrocarbons at the radiator cap.
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