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Discussion Starter #1
Well,

A few months ago my 2000 zx3 was having problems keeping temp on the highway at speeds above 70mph. So...

I replaced the entire cooling system.

It seemed to work well for a while but would still operate hotter than normal while cruising at highway speeds.

Today on an extended highway trip while cruising at 70mph for around an hour, the dummy temperature gauge begins to move towards the red. Upon slowing to 60mph, the dummy gauge returns to its normal position (a hair to the left of center)

Considering the entire cooling system is brand new, there are two things I can think of that might be causing this but both of them don't seem to fit.

1. The engine is running lean. My reasoning? I get 35-37 mpg on the highway and the car is rated at 33mpg. A lean running engine will run hot. However, I figured I would get a code thrown at me if the engine was running lean. I haven't gotten any codes.

2. Perhaps somewhere in the hoses of the coolant system, there is a partial blockage and causing the coolant to become too hot to sufficiently cool the cylinders.

Fellow FF'ers, I have posted about this problem before and am at my wit's end. I am pretty well knowledged in this area because I have researched it extensively to try and figure out the problem and still am unable to enjoy my otherwise PERFECTLY running Ford Focus. If anyone can correctly help me diagnose and fix this problem, I am liable to send you some sort of gift basket.

If you would like to talk to me about this over the phone, shoot me an e-mail at [email protected] and I will give you my number. Yes, this problem has brought me to desperation. I will give it one last shot to fix my problem.

PS - If anyone says "check the fans" or "thermostat" I will find you and replace your engine with an SPI engine so help me god.[gunfire]
 

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Have you actually checked the temp with an infrared thermometer ? The temp gauges on the Focus are not very accurate. I am sure you know by now its just a. Cyl head temp. Not an actual coolant temp. If every thing has been replaced. With an IR thermometer you can check different parts to see what it is actually running. Has it ever boiled over ?
 

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It hasn't boiled over however I do know that that sensor is working properly. I made a thread a while ago asking people to report their CHT while on the highway. When I travel at 70mph my CHT is pushing 109* C. That is the same temp that triggers the dummy temp gauge to start climbing to the red :(

This is only on the highway. I test drove another focus to see if I was going insane and its temp on the highway stayed at 91* C. I am pulling my hair out. And the more I talk about it there is always that voice in my head saying that it could be the head gasket. But then, wouldn't it overheat sitting in traffic or around town? Because it keeps perfect temp during those situations. It can sit in traffic for 24 hours on a 100 degree day and be fine.

I'm going to start drinking.
 

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I have the exact same problem. I have a scanguage II hooked up and the highest I've seen on the highway was 117c, then it would cool down to 90-89c when off the throttle coasting in gear or idling. (which is when my stat opens/closes)
Then after an oil change a few weeks ago from 5w30 to 5w20 it doesn't really go past 114c. (wasnt expecting that) But still too high for my liking. Then I noticed my fans didn't come on at all. Tested them and found they work so I checked the resistor which was rusted to crap and replaced it. Now they work only when the a/c is on. Fuses are all okay and I assume the relays are okay.
My next thing to check is the CHT sensor but how do I do that? (btw the temp needle "always" stays in the middle when warmed up)
 

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I have the exact same problem. I have a scanguage II hooked up and the highest I've seen on the highway was 117c, then it would cool down to 90-89c when off the throttle coasting in gear or idling. (which is when my stat opens/closes)
Then after an oil change a few weeks ago from 5w30 to 5w20 it doesn't really go past 114c. (wasnt expecting that) But still too high for my liking. Then I noticed my fans didn't come on at all. Tested them and found they work so I checked the resistor which was rusted to crap and replaced it. Now they work only when the a/c is on. Fuses are all okay and I assume the relays are okay.
My next thing to check is the CHT sensor but how do I do that? (btw the temp needle "always" stays in the middle when warmed up)
The 5W-20 vs the thicker 5W-30 will cool the engine better as it is a faster flowing oil which transfers heat faster. Thick oils are not what some crack them up to be.
 

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The only way I know to check the CHT is to use an infrared thermometer to check the heat of the radiator hose at the thermostat against your Scangauge readings. Expect it to be different, but you're looking for extreme differences. I've had trouble collecting data from people with known bad CHTs. These are the people's whose gauges jump suddenly while driving. I would expect extreme and unrealistic temp jumps in this case, but I don't know how high it would go.

Depending on how old the car is, your overheating problem might not be the fans or the cooling system. It could be things like clogged catalytic converters or internally broken mufflers. You'd have to look for other signs that you have exhaust blocking to determine that. Low coolant flow will do it also- like a water pump that is past it's prime. I'm not personally going to recommend WP replacement unless there is a definite sign that the part is bad.

Overheating while driving is not a cooling fan problem. Those cooling fans don't do anything while the car is moving. The fan motors are designed to over run if the blades spin faster than the power would allow. That's why you have diodes. I recently discovered that the temps for the fans are 105C for low speed, and 111C for high speed. You should make sure that the fans are coming on at low speed while sitting and idling after driving. IF not, then replace the fan resistor located between the 2 fans. The fans will operate on high speed with the AC on, or if the temp reaches 111C.
 

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My exhaust is a SVT exhaust front to back, so it's perfectly fine. And my resistor has been changed, like I said. The fans didn't work at all before then and they still don't unless I push the A/C button. I understand that the fans working won't help me at highways speeds but I want them working ASAP and then I'll move on the my overheating problem by probably flushing the system and possibly taking the water pump off to check it. And I guess I'll get an infrared thermometer.
A few months ago I changed the thermostat that was stuck open and housing that was leaking and noticed a lot of broken plastic from it got into the system. So maybe that's a cause?
Thanks for the input btw.
 

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Broken pieces of plastic is a problem in the cooling system. It could clog the radiator. A clogged radiator is something I failed to think of that could overheat the car at any speed.
 

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Is the water pump new? Plastic could be from impeller breaking up.

Plastic clogged in strategic spots could very easily cause this trouble.
 
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