Zetec Cooling System Questions - Normal Temperature Range and Parts Reference

[Slonie]

I've been all over the web on this but as I finally have a more accurate temperature gauge and my car's back together, I'm wondering what kind of water temperatures people see on a Zetec (Blacktop, via Caterham USA), or what they'd consider an upper bound for normal running.

 

The baseline of my setup is a 93C-on 87C-off fan switch installed in the top of the radiator, a Ford thermostat marked 92C, and a Stack temperature gauge reading from the OEM gauge sender location in the bottom of the thermostat housing. My cooling system is what I'd describe as (probably) stock Caterham USA Zetec setup, with a heater. Fully pressurized system with an expansion tank. I had a whole series of cooling misadventures due to a faulty fan switch and temperature sender that put my car out of commission for ages, and I have recently gotten it back together with (mostly) new cooling hoses, thermostat, fan switch, temperature sender and gauge. I could write a whole post about my research and misadventures with the Caterham OEM gauge but I can shorten it to say - It was not accurate, and I replaced it with a Stack Pro-Control (electronic) gauge.

 

Prior to installation I tested the fan switch in a pot of water and confirmed operation, as well as tested the Stack gauge+sender up to boiling water (i.e. 99C). The gauge read about 2 degrees high in the area of ~80C and maybe 5 degrees high at 99C (it indicated 104C).

 

I've driven about 60 miles since getting the car back together and seen my indicated temperature while driving fluctuate between an indicated 96-98C. I think per my testing above that the real temps are a little lower. If I am going slow uphill or stop and idle, the temperatures will go up until the gauge hits about 102C before the fan eventually kicks on and brings it back down below 100C.

 

I'm a little surprised at how late the fan kicks on given the temperature rating of the switch, and have surmised that maybe the coolant has actually dropped a few degrees by the time it makes its way along the upper rad hose and into the radiator. This has caused me to wonder about relocating the switch so that when my fan comes on it's actually coming on when thermostat housing temps are at ~95C. I'm also planning on adding a manual override switch on a relay so that I can turn it on myself for peace of mind when I expect to be slow or stopped frequently.

 

I've also noticed that coasting at engine idle speed doesn't seem to cool as well as being at 2500rpm or so, this maybe makes sense given the water pump operation being RPM-dependent.

 

All this being said though, and back to my original question: I've read some people online saying that temperatures near 100C or even above are actually normal for Zetecs in which case I may have nothing to worry about. I haven't really driven the car much above 4000rpm or particularly hard yet while shaking down the cooling system after the car was idle for quite a long time. And to be clear, I've only seen it go over an indicated 100C while moving for the briefest of moments, in general it seems to be sitting at 96-98C in my 30-40mph driving.

Edited June 13 by Slonie

[Slonie]

I'm also happy to discuss the Zetec cooling system at length here, including the diagram I drew of mine. I need to transfer overall of the measured sizes to make this a truly useful reference, but I believe it to be accurate. 

 

As an addendum (to be added on a future version along with all the other hose dimensions -- I'll probably make another post about which off-the-shelf radiator hoses I used and a call for better suggestions) -- My car used 5/8" heater hose for the lower bypass and all the heater lines, but the Zetec thermostat housing outlets are not actually 5/8 -- they're more like 3/4 (19-21mm). When I redid the lines I actually used a 19mm elbow for the bypass then used a coupler to reduce it to 5/8 for the rest of the run. For the heater hose feed from the thermostat housing, the line is not actually a plain 5/8 hose at all but a Gates 3638. That seems to be a replacement part for a Euro VW Golf. 19mm on short side 90 degree bend, 15.5mm other side. When I replace that one, I may order another of the same, or simply get a 19mm elbow and reducer again as I did on the bypass.

Edited June 13 by Slonie
Added more detail about the hoses depicted in the diagram

[Vovchandr]

Very impressive diagram. That should be added to the tech files on site.

 

After the plethora of cooling issues with my Zetec I've ended up having everything dialed in at the end.

 

My OEM temp gauge has the fan kick on around indicated 80 and car actually runs on the cooler side most of the time now.

 

I strongly recommend a see through coolant filter for troubleshooting cooling issues instead of doing it literally blind and having it pass a pressure test before going too far into sorting out other issues.

[Taber10]

Thanks for the diagram--really neat to see the system drawn out.  I can't answer the question, but I want to add that getting my fan to come on while underway is very difficult.  I have to sit stationary in the garage and rev the engine to get the temperature up to operate the fan.  Also, I have had three temperature guage sending units, and found that the "eBay" switches were at least as reliable as the Ford switch that came on my Zetec SVT and MUCH cheaper.  The Ford parts counter employee wanted me to get the date when I purchased the second one, as she thought it would be under warranty and at the time--several years ago--the Ford switch had gone from about $32 to about $34 for the third one.  One of them failed in about a week, so I relied on eBay for about $8.  

[MV8]

Oem engines run hot in part to improve emissions. A zetec stat starts to open at 95c and is fully open by 106c, with the fan on at 105c (221f) or if the AC compressor is engaged (necessary to ensure enough airflow across the condenser to aid control AC compressor head pressure, not engine cooling). I would run an 85c stat with a fan switch that opens at 90c and closes at 95-100c.

[Slonie]

5 hours ago, MV8 said:

Oem engines run hot in part to improve emissions. A zetec stat starts to open at 95c and is fully open by 106c, with the fan on at 105c (221f) or if the AC compressor is engaged (necessary to ensure enough airflow across the condenser to aid control AC compressor head pressure, not engine cooling). I would run an 85c stat with a fan switch that opens at 90c and closes at 95-100c.

 

 

The thermostat I purchased (to replace the one that came with the car) is a Motorcraft-RT1150 (ford p/n F8RZ8575CA )

If you know the part number for an 85c stat, I'd definitely swap it in at next system drain (which I'm planning to do sooner rather than later for flushing purposes).

 

For thermostat housings, I haven't had an issue yet, but this could be useful info for future reference. I had read that Focus Zetec thermostat housings are prone to cracking/leaking, and previously went through a bunch of research on the SVT Focus forums to find "the good part numbers" for an improved housing. Then I realized that whomever built my engine already had already spec'd these parts.

 

In my research I also found the Bostig billet thermostat housing for Zetecs which is quite expensive and possibly NLA, as well as the Sólido Frio cast aluminum housing, which seems to re-create an older Ford part before they switched to plastic. That may be worth a look if the OEM housing ever fails.

 

(Thread: https://www.focaljet.com/threads/who-wants-to-be-a-guinea-pig-stat-housing.621238/page-2?nested_view=1&sortby=oldest )

(Comparison: https://www.svtperformance.com/threads/thermostat-housings.986357/ )

(Youtube comparison: https://youtu.be/n8YyPVsVfgQ )

 

F8RZ-8592-AG (thermostat housing body)

F5RZ-8592-A (thermostat water outlet bolted to main body)

F8CZ-12A648-AA (temp sensor on top of body for OEM ECU, I don't know if it's what I have as used with a Pectel)

W500015-S309 x3 (bolts for water outlet)

W700319-S300 (thermostat O-ring/gasket)

F8RZ-8575-CA (thermostat)

[Slonie]

For a fan switch, I'm running a a Borg Warner/ Wahler 601092D

It's marked 92/87c and it used to be available on FCP Euro but is no longer there.

 

 

Incidentally, I've tested this my 92c switch in a pot of heated water and confirmed its operation at ~93C, but in the car it doesn't seem to actually kick on until I'm at around 100c at the thermostat housing. I can only guess that this is it's because the temperature drops across the run of the upper radiator hose, but it's still curious. 

 

The OEM Caterham switch I got from Rocky Mountain Caterham would theoretically be a 86/95 switch, although my pot-of-water test seemed to be more like 98-86\

 

In the end, I will probably wire up a relay and use the Stack pro-control gauge to provide an override, along with a manual switch.

[MV8]

I think standard replacement plastic stat housings are fine. Older, all metal engines are more forgiving of aggressive hose replacement, hose routing that is putting a side load on the barb, or overtightening when the o rings should be replaced. It is easy to break plastic by not lubricating the barbs when initially installing hoses or not rotating the hoses on the barbs to break the grip before removal. If a hose is being replaced, just use a razor blade to cut along the length of the barb to peel it off.

82c/180f stats: Stant 13978 or Motorad 5270180 or 270180, gates 33338 to name a few.

If the stat fails closed, the fan may not come on automatically if the fan switch is in the upper hose between the stat and the radiator. The oem coolant temp sensor takes up the ideal location but you could tee into the bypass as close as possible to the stat housing to add a fan switch and a sensor for the gauge. It can be a suitable size pipe drilled and tapped as needed to fit both sensors. A single terminal sensor for a gauge will need a  ground wire added to the pipe.

[Slonie]

Thanks @MV8 as always for the tips. I found a photo of my old stat (which I suspect is actually fine,, but changed anyway to a new 92c Motorcraft  because I had the system drained). Sure enough, it's marked 92-106. I'm sure switching to a cooler stat will keep my temps a bit lower. I ordered a 33338, which starts at 82c, I'm not sure what the total range is but figure it'll be fully open by the time I'm in the mid-90s.

 

Edited June 14 by Slonie
To make it clear it's an old photo, not that I changed any parts

[MV8]

I was pleasantly surprised to find the Mazda 2 5spd (100 hp 1.5L mzr dohc vvt) I recently bought for my wife comes with a 180f stat, oem. No temp gauge though; just a blue light when cold and a red "call a tow truck" light. I will be adding a temp gauge.

[Slonie]

New stat arrived, Gates 33338, funnily enough despite being a Gates package the thermostat itself was marked Motorad / 0422 so I guess that’s two parts cross references into one. Hopefully I’ll get it in this weekend and be able to report back with lower temps. It’s gonna be a hot one (forecast is in the 90s…). 
 

 

[Slonie]

Got the new 'stat installed last night. A few observations.

 

1) The stat I just pulled was also 92c but marked 92-102 and not 92-106. It was a current Motorcraft part (as noted above: Motorcraft-RT1150 (ford p/n F8RZ8575CA )

2) I went for about a half hour drive in admittedly cooler temperatures than my previous drives since the sun had gone down (71F ambient instead of 78F the last time I took note). First impressions are that my cruising temps went from 96-98 indicated to 88-90 indicated, never climbing above 90 as long as I was moving. Exactly the kind of improvement I was looking for.

3) When stopped with the fan off, temperatures would again creep back to 102 indicated before the fan kicks on. But it took longer and wouldn't get there at the average stoplight, I think.

4) When I stopped and let the fan run, temperatures would continuously go down (to about 92). Previously the fan would slowly bring it from 100-102 down to 98 but I never saw lower. 

 

So, with the caveat that I need to drive it on a hot day to be sure, I'm calling this a success. I still wouldn't mind having the fan kick on a tick earlier, but a future override switch should take care of this. Thanks again @MV8 for the encouragement to try it and the part number. Now I've got a lot more confidence to go back to some real driving this weekend and next...

 

Photo: Idling in front of my garage with lower temps than I could get while moving at 40mph before:

[Slonie]

Also note: As promised by many people who've been down this road, the Stack LED-lit gauges are incredibly bright, I don't have a dimmer switch or resistor on it to bring it down, that's filed under "maybe once I replace all the gauges with matching units"