Temp gauge moves hotter going down highway - Ford Bronco Forum
 
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post #1 of 20 (permalink) Old 02-27-2009, 01:23 PM Thread Starter
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Temp gauge moves hotter going down highway

I have flushed the system, ran a system cleaner for a week, about to replace the water pump due to weep hole leak, new radiator cap, new 195 thermostat, according to the electric aftermarket gauge the temp is around 200-205 degrees when warmed up if you keep it under 50 mph once you hit 60-70 mph the gauge moves to 207-209. The gauge only has a 180 and 210 mark so I am guessing on the exact temps. It has two electric fans on the radiator and no clutch fan which appears to keep the temp under control at idle. Is this in normal range for the temp to rise at highway speeds? everything I know tells me it would rise at idle but this is not the case. I am wondering if the gauge is off because when I check the block with a infrared thermometer the temps are closer to 185-195 degrees nothing appears over 200 degrees. The gauge also is very sensitive because you can actually watch it move as the truck heats up and cools off. I am just a little concerned since I recently bought this truck and fixed a blown head gasket. There was another electric fan on the motor side of the radiator that was not working so I took it off. I dont think the fan would matter at highway speeds. Please enlighten me if the extra fan will help, or if I might have other issues or am I just overconcerned? I am having no other issues otherwise.

What has me puzzled is the rise in temp at highway speeds.

Thanks in advance !!
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post #2 of 20 (permalink) Old 02-27-2009, 01:58 PM
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It's not clear what type of vehicle, year and engine you have.......double check voltage/resistance at Temp Gauge for continuity first....

Fan and belt tension......

It could just be the "temp gauge sending unit" usually located in the lower intake manifold towards the front with a single wire on it which might be giving a false reading.....it's brass with pipe style threads, so be careful if you replace it not to over tighten it or you'll crack the manifold, just until it feels snug with a ratchet...OK ......lol lol use Permatex on the threads and you're good to go.....

Check the T-Stat housing for leaks on the bottom then check all hoses, heater core box AND I would even check all the freeze plugs to see if there is a rusty one that is slow bleeding......just a thought....

Depending on the age of the engine steel, I don't like chemical flushes because they can be a bit harsh and loosen/remove some of the steel scale inside sending it through the water jackets causing blockage and thinning out the steel which might contribute to over heating down the road, I'm not saying that's what happened here but just a heads up for the future just use clean water when flushing the system .........it's cheaper......

With the cap off, if the water in the radiator neck is "racing " when the engine is running it could be an indication of head gasket problems, especially if it happens right away........

Good Luck ~
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post #3 of 20 (permalink) Old 02-27-2009, 02:00 PM
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weird.i would first suspect a bad elec. gauge.(you said the infared them. read closer to normal op. temps.)
ditch the electrical gauge and run a mech. temp gauge.they are rarely off, and will tell you the temp. even after you shut the truck off.
if it ain't the gauge's fault, chunk the elec. fans, and go back to a clutch fan.

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post #4 of 20 (permalink) Old 02-27-2009, 02:05 PM
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What core radiator?
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post #5 of 20 (permalink) Old 02-27-2009, 02:07 PM
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Quote:
Originally Posted by JKossarides View Post
It's not clear what type of vehicle, year and engine you have.......double check voltage/resistance at Temp Gauge for continuity first....

Fan and belt tension......

It could just be the "temp gauge sending unit" usually located in the lower intake manifold towards the front with a single wire on it which might be giving a false reading.....it's brass with pipe style threads, so be careful if you replace it not to over tighten it or you'll crack the manifold, just until it feels snug with a ratchet...OK ......lol lol use Permatex on the threads and you're good to go.....
Check the T-Stat housing for leaks on the bottom then check all hoses, heater core box AND I would even check all the freeze plugs to see if there is a rusty one that is slow bleeding......just a thought....

Depending on the age of the engine steel, I don't like chemical flushes because they can be a bit harsh and loosen/remove some of the steel scale inside sending it through the water jackets causing blockage and thinning out the steel which might contribute to over heating down the road, I'm not saying that's what happened here but just a heads up for the future just use clean water when flushing the system .........it's cheaper......

With the cap off, if the water in the radiator neck is "racing " when the engine is running it could be an indication of head gasket problems, especially if it happens right away........

Good Luck ~
I am pretty sure that using permatex on electric sending units make them send false temps.
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post #6 of 20 (permalink) Old 02-27-2009, 02:18 PM Thread Starter
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This is a 1979 Bronco chassis with the 351M. The body is a 1955 Ford truck. I cannot run the clutch fan due to clearance issues. The best I can tell is the radiator is from the bronco and looks to be three core (stock radiator). I am leaning towards a mechanical temp gauge anyway so I will look at that. I did flush the motor and block with water first and then ran the flush/cleaner (not the harsh chemical type) for one week. This temperature fluctuation occurred with water, flush/cleaner and now coolant. Would the temperature sender be faulty or do they just stop working. I did not think of the sender since the gauge is registering a temperature. I am leaning towards the gauge/sender being faulty, just wanting second opinions.
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post #7 of 20 (permalink) Old 02-28-2009, 03:30 AM
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TdmayfieldIV:

So you don't think the constant hot/cold temperature and corrosion they're subjected to over a long period or that they're made out of cheap brass which costs about $10.00 wouldn't contribute to a false reading.......?

I just swapped in a new 302 long block this Sept.. and mine works fine, I've been doing it for years and never had a problem........besides once you thread the unit in it would thin out the Permatex but leave enough to keep it from leaking and still be conductive, brass and aluminum........

So what would you recommend Brother.........................?
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post #8 of 20 (permalink) Old 02-28-2009, 08:54 AM
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Reading a temp of 185 to 195 degrees F on the engine block with an IR gun tells me your gauge is reading right. The heat is generated inside the engine, surface temp is always going to be a little more cool than the inside.


A backwards head gasket will cause the problem you describe. Are you sure you put your head gaskets on right? The tab marked front goes to the front of the engine.

Opportunity is missed by most people because it is dressed in overalls and looks like work- Thomas A Edison
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post #9 of 20 (permalink) Old 02-28-2009, 09:04 AM
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Quote:
Originally Posted by JKossarides View Post
TdmayfieldIV:

So you don't think the constant hot/cold temperature and corrosion they're subjected to over a long period or that they're made out of cheap brass which costs about $10.00 wouldn't contribute to a false reading.......?

I just swapped in a new 302 long block this Sept.. and mine works fine, I've been doing it for years and never had a problem........besides once you thread the unit in it would thin out the Permatex but leave enough to keep it from leaking and still be conductive, brass and aluminum........

So what would you recommend Brother.........................?
Easy: Loctite 567

http://www.henkelna.com/cps/rde/xchg...UID=0000000JBE

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post #10 of 20 (permalink) Old 02-28-2009, 11:20 AM Thread Starter
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I thought of that ,but I remember making sure they were put on properly because they were clearly marked FRONT on the gasket. I will replace the water pump and see if that makes a difference. I believe I have flow issues either from worn out waterpump( mabey the fan blades are rusted/corroded half off ) or partially clogged radiator. I will do one thing at a time so I will know what helps. Would a 180 thermostat help bring down the temp or will that just be masking the problem? On the IR thermometer I wondered about the accuracy of the core temperature when taking surface readings. Thanks for the replies.
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post #11 of 20 (permalink) Old 03-01-2009, 10:21 AM
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in the past i had a f100 with a 4.9L that i had rebuilt. i kept having issues with the temp going up when i went over 55mph. i ended replacing the entire damn engine with a new one....and it still kept heating up over 55mph. it turned out that the radiator i was using was clogged even though i had flushed it twice. once i replaced the radiator everything was working great. i also just took the thermostat out and ran it without one. it ran so cool the temp gauge barely even registered. hell, i even drove it 15 miles in city traffic with a busted water pump belt and it never ran too hot. just something to consider.
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post #12 of 20 (permalink) Old 03-01-2009, 04:25 PM Thread Starter
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Thanks for the info. I will replace the water pump this week and then see if anything changes , if not then I am going to seriously look at the radiator and possibly replace or get it boiled out. I am taking one step at a time to be able to tell what solved the issue. I will update if and when the problem is resolved.
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post #13 of 20 (permalink) Old 03-01-2009, 07:56 PM
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Quote:
Originally Posted by 55 Bronc-Up View Post
There was another electric fan on the motor side of the radiator that was not working so I took it off.
are you sure the fan that is on the outside is set up to be a pusher and not a puller? Maybe the previous owner installed it wrong. I would think a fan on the motor side set up as a puller would be much more effective.

Quote:
Originally Posted by 55 Bronc-Up View Post
What has me puzzled is the rise in temp at highway speeds.
even with a properly working cooling system, if there is insufficient airflow into the radiator fins, your temps will climb on the freeway. I have a car that does that also. Restricted airflow could be due to the fan on the grill side of the radiator. It is blocking air. Like I said earlier, a motor-side puller will be better if you have room for one. How much room (in inches) do you have?
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post #14 of 20 (permalink) Old 03-01-2009, 07:58 PM
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It's like anything else.

Quote:
Originally Posted by 55 Bronc-Up View Post
Thanks for the info. I will replace the water pump this week and then see if anything changes , if not then I am going to seriously look at the radiator and possibly replace or get it boiled out. I am taking one step at a time to be able to tell what solved the issue. I will update if and when the problem is resolved.
Fix what you know is broken first(your water pump) then move on to other components if that doesn't fix the problem.

I would suggest if the rad and heater hoses are old at all this would be a great time to change them as well.

Also someone mentioned the temp sender, it is my personal experience if that wire is not tight with a good clean connection it will read all over the place.

Also as a side note I believe I even read in the owners manual that there was some upward movement of the temp gauge and that this was normal operation.

If you have an owners manual have a look.


Rick.
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post #15 of 20 (permalink) Old 03-02-2009, 06:38 PM
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i have seen timing issuses cause the same problem. if you have pinging while mashing the gas.....try backing off (retarding) timing.
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post #16 of 20 (permalink) Old 03-03-2009, 08:58 AM Thread Starter
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Thanks for all the replies. I replaced the water pump and decided to pull the radiator while it was drained and have it cleaned and rodded out. The passages were really corroded, I originally only looked in the cap opening, but after looking in the inlet and outlet openings I could see alot of build up. I think this is my flow problem and will let you know if it solves the problem when I get it back together.
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post #17 of 20 (permalink) Old 03-03-2009, 09:29 AM
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I have a 400 in an EB trail rig and fought a lot of overheating issues at first. When I installed a big honking electric puller fan/shroud and removed the mechanical one, it was a little improved at trail speeds and fine at idle..but overheated like crazy at highway speeds. With the mechanical fan, it was the opposite..overheated while idling or crawling slow but fine on the highway.

I ended up solving the problem by going to a large clutch fan, a custom shroud for that, and a smallish pusher in front of the raddy to help when crawling hard and slow.

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post #18 of 20 (permalink) Old 05-11-2009, 03:40 PM Thread Starter
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Update on the temp issue. Sorry for it to take so long, but I hate to leave things unanswered/undone and wanted to have good info to reply with.

I have verified that the head gaskets are on correct by finding the 1/2 inch tab sticking out at the lower front edge of each head between the block and head. I have rodded the radiator and cleaned entire system. I did replace the thermostat that I originally had with a thermostat that has the "hat/flange" on the bottom to cover the round casting opening in the block that can be seen through the thermostat housing (This alone really stabilized the temperature fluctuations).

I added a taurus fan for additional air flow and it did not affect running tempemperature at all so existing fans were sufficient and have since disconnected the taurus fan.

I have noticed that the longer the engine is running and has time to completely warm up the gauge moves very little whether idling or driving down the highway. We have had some high 90's last week and nothing changed with the way it performed even with the warmer outside temperature.

Bottom line is that the truck is not overheating (never was) and running great and the temperature swings indicated by the gauge are minimal now with new thermostat (indicating a improper flow issue with first one). I suspect that the gauge is a little off (reading 10-15 degrees higher than actual temp and very sensitive).

So I have decided that the wrong thermostat and sensitive/faulty gauge are the issue and something I can live with.

I have done each of these changes individually to determine what effect each one had on the issue.

I have decided that this is normal for this truck and short of replacing the gauge I will accept it as "normal operating temperature".

The reason I have not replaced the gauge is that it matches the others and I cannot find a mechanical replacement to fit the aftermarket gauge cluster.

Hope this is helpful info and thanks for all the replies to the original post.
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post #19 of 20 (permalink) Old 05-11-2009, 06:06 PM
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For people trying to dianose their cooling- with a properly functioning cooling system, a fan is not even needed at highway speeds. If your temps are rising even at highway speeds, you can rule out the cooling fan as they only help when the vehicle is not moving or is not moving fast enough to create sufficient air flow through the radiator.
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post #20 of 20 (permalink) Old 05-15-2009, 03:40 PM
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hot at hiway speeds

I had the same issue with my 83 with a 302 in it. I found out that because of the ethanol in our gas in MN the engine would start to lean out at Hiway speeds and raise the cylinder temps. I had to increase the primary jets one step to compensate for the alcohol in the gas.
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