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Discussion Starter #1
With help from this site and Huskinhano, I put together a 1999 GT40P with Ford E303 cam and TFS spring kit. The engine runs very well. My issue is that my temperature is erratic. It will slowly go to 180, then shoot up almost immediately to 230 then down to 160 and repeat, ad nauseum. It’s only about 40-55 degrees out where I live currently. I’ve tested with two mechanical temp gauges and both respond the same way. I think something is going on with hot spots from air bubbles or a clogged radiator?

The champion 4 core radiator is about two years old and I ran it with my old 289. The 289 had tons of crap in the cooling system and I flushed it several times before installing this 4 core radiator, but, it still had some junk in it. I’m wondering if my problem may be a clogged radiator. I have called around restoration shops locally and no one knows where I can get a radiator cleaned anymore, as these places have all closed. I’d hate to have to replace my radiator again since it’s pretty new.

Everything but the radiator in the cooling system is new: stock style water pump, new radiator hoses, new 13lb cap with lever release, new heater core. I have tried three different thermostats, a high flow racing 180 (wouldn’t get up to operating temp), a stock 195 (gauge bounced around) and a 180 (gauge still bounces) which I am currently still running. I drilled one small hole in the stat to try and help burp the system before install.
The engine runs points ignition, 14 degrees initial timing.

Here’s what I’ve checked so far:
  • Pressure tested the cooling system to 17 psi and found no leaks
  • Ran car up to temp with radiator cap off to try and bleed system
  • I’ve now installed an inline heater core filter, and a radiator aeroflow filter to help clean the system
  • Repeatedly pulled radiator cap release lever once system is pressurized in an attempt to bleed air out
  • Run a snake camera down each cylinder to check for cylinder wash from antifreeze
  • Cold cylinder compression tests are all 160-165 psi
  • Cold cylinder leakdown tests are all in the 1-3% loss range
  • No cross contamination that I can see of oil/antifreeze
Anything else I can check before I shell out money again for another new radiator since I can’t get my current one cleaned out? I'm at my wits end.
 

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Maybe a faulty thermostat?
Where is your engine temperature sensor located?

The fact that it’s cooling down tells me that the radiator is doing a good job.
 

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I have a 195* thermostat in my engine with a mechanical gauge. After a cold start I can watch it slowly climb to about 210* and then it suddenly drops to about 180* before it starts to climb again, stopping at about 195*. It may swing up and down again about 20* before it finally settles down in the 190*-200* range. I consider this variation normal until all of the coolant has circulated through the engine and radiator and has finally reached a constant temperature.
 

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Discussion Starter #5
My temp gauge is mechanical and it never settles into a temperature. It just consistently swings back and forth in the manner I mentioned above. The sensor is located on the intake manifold right behind the thermostat housing. I've had a total of 4 thermostats in the car at this point. 3 have had the same erratic temp issue. the forth was the racing 180 i mentioned that is high flow and never allowed the car to get up to operating temp.
 

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Are you using the heater when it does this?
Is the bypass hose, from thermostat housing to water pump, connected properly?

Or maybe the entire cooling system is functioning properly and the problem is the temp gauge?
 

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Discussion Starter #7
Are you using the heater when it does this?
Is the bypass hose, from thermostat housing to water pump, connected properly?

Or maybe the entire cooling system is functioning properly and the problem is the temp gauge?
The heater core hoses and bypass hose are connected properly and are new. I have tried two temp gauges that both register the same erratic temp issue. The issue happens with the heater on or off.
 

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Discussion Starter #8
I ended up putting in a flowkooler hi flow pump hoping the increased flow in my block might get rid of hot spots - no such luck. still having the same weird temp issue. :mad::confused::mad:
 

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Now that I've read the post.... again.... my guess is an air bubble. If you've "burped" it and it still does it I'd grab a combustion gases test kit..... :-(
 

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I had two different 180 degree high flow mr gasket thermostats in my car that were opening way to early and not letting my engine get past 160 degrees. At first I thought it was the temp gauge. Put a new gauge in and had the same issue. Changed to a motorcraft 192 degree stat now after it cycles the 210 and back down to 180 or so a few times it finally settles at 192 degrees and stays solid.
 

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The factory gauges are "dampened" so that they react slowly to small change. How would you like to see your fuel gauge swing every time you went around a corner or up a hill? Your mechanical gauge is not dampened.
What happens if you get on a highway where you can maintain a constant speed for at least 15 minutes? Does it ever settle down? If it's not overheating why are you worried?
 

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Discussion Starter #13
The factory gauges are "dampened" so that they react slowly to small change. How would you like to see your fuel gauge swing every time you went around a corner or up a hill? Your mechanical gauge is not dampened.
What happens if you get on a highway where you can maintain a constant speed for at least 15 minutes? Does it ever settle down? If it's not overheating why are you worried?
I'm worried that it will overheat when the temp warms up outside. It's only about 40-50 F now out. No, the gauge never really settles, it's so odd. Yesterday, it would sit around 160, then sloooowly go to 180 then BOOM 260! The immediately right back down to 160 and repeat, ad naseum. It never settles into a temperature.
 

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Discussion Starter #14
Now that I've read the post.... again.... my guess is an air bubble. If you've "burped" it and it still does it I'd grab a combustion gases test kit..... :-(
Wouldn't the leakdown, compression or cooling system pressure tests I did tell me if I had a cracked head or similar issue? I'm at a loss here.
 

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Discussion Starter #15
The gauge never stays at an overly hot temp. If it hits 260, it does so in a swinging motion. 180 straight up to 260 then straight back down to 160.
 

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65 Fastback 289 4 spd, 65 convertible 5.0L 5 spd. 3.73 8.8
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The gauge never stays at an overly hot temp. If it hits 260, it does so in a swinging motion. 180 straight up to 260 then straight back down to 160.
Does this happen just sitting still? What happens if you leave the radiator cap off. does it puck antifreeze out? These engines are not hard to bleed, U could put an aspirin in tstat to bleed, but usually if you leave a heater hose on top intake loose you can bleed it. The biggest problem when people fill radiator for first time they fill to top and then it pucks it out, I fill with maybe 4 qts. or just so you can see the coolant about half way up the radiator, and when the tstat opens start dumping in, not filling to top until temp stabilizes.
You could go buy a infarred temp gun, check temp at top and bottom of radiator, check at intake behind the tstat. It sounds to me like you have a head gasket issue, like someone else said. Then you need a carbon monoxide tester in radiator cap. Which I have experienced one time they will test good and next time it won't. The key to that is drain the radiator a little so antifreeze won't get into fluid to give you bad result.
 

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If it's not an air bubble causing coolant to get hot in some area then burp by, show hot then cool again, I'd guess the sending unit itself may be at fault or a wire is temporarily grounding to peg the gauge.
 

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The only thing that could cause swing in temperature like that would be the circulation stopping and then moving which automatically makes you think of a bad thermostat which you have replaced.

Do you have the thermostat in correctly with the sensing bulb facing rearward? Another possibility is the lower hose collapsing from the suction of the water pump. That is why they come with that wound spring inside of most lower hoses.

The only other thing is your gauge setup. You said a "mechanical gauge"? Do you mean a gauge with an actual copper line running to it like a mechanical oil pressure gauge? If it operates on electricity its not a mechanical gauge. You need an infrared thermometer to verify the actual engine temperature.

Don't let it get to 260 degrees. Its going to warp parts, especially aluminum heads. I had an aluminum head warp and start leaking coo ant. with a factory gauge that just went to the 3/4 mark from a faulty thermostat.
 

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The only thing that could cause swing in temperature like that would be the circulation stopping and then moving which automatically makes you think of a bad thermostat which you have replaced.
Not true. An air pocket or low coolant can also make the temp sender read cold (no coolant in contact with it) then as soon as a shot of coolant goes past it will shoot right up.
 
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