Cooling system questions: Fan, t-stat, rad

[KevAndAndi]

When my '81 FI idles in the garage, the fan eventually comes on, but then it never stops running until after the engine has been turned off. (The temp never goes above 190F.) This is abnormal, correct? I've seen many posts mention the fan cycling on and off during idle, but it ain't happenin' for me.

By the way, I intend to do some cooling system upgrades anyway. The rad looks to be original, and with replacements relatively inexpensive, I plan to replace it. I also already have a stainless heater pipe on the way from Mark. I will do a system flush before replacing rad, hoses, and heater pipe. I will also assess whether to R&R the water pump and/or t-stat.

Lastly, what are folks' thoughts on low-temp (175F) t-stats? What are the considerations when weighing a low-temp t-stat versus a regular one?

Thanks!

[azruss]

I have an 80 FI. It is normal for the fan to cycle on after the car has been turned off. I rebuilt my entire system with new t-stat, water pump, radiator, 13 psi cap, heater valve, hoses, and heater hose fill port. I went with the standard t-stat and added a manual radiator fan switch which i have never used. I also drilled a 1/8" hole in the T-stat valve. I removed the AC so the radiator would have full access to the cool arizona air I am running an aggressive air dam that is getting lots of air to the radiator. The cooling system performs beautifully. Excessive idling will raise the temp no more that 10 degrees. I take the car out on slow cruises (20-25 mph) on 110+ degree days with no cooling issues. There is a difference in quality of water pumps. Talk to Ramzi and Csaba about that. The radiator and stat I bought from AR. the heater hose fill port from NAPA. I put a flat hood on my car that required me to modify the radiator with a short neck. The secret to the sauce is to have the system air free.

[4uall]

just did mine recently the fan staying on after the engine is off is normal the regular temp switches are fine, left the water pump, did not flush system, just drained and replaced rad and hoses

http://fiatspider.com/f08/viewtopic.php ... a&start=15

[baltobernie]

(The temp never goes above 190F.)

Certainly replace weak or hard hoses, and the OE heater pipe can be a weak link if PO's haven't been diligent with coolant maintenance. Otherwise ... If it ain't broke, don't fix it.

[KevAndAndi]

Thanks for the responses. Just to be clear, the problem is not that the fan runs after the engine is shut off. It is that when the engine is running, the fan comes on at the appropriate time, but it never cycles off while the engine is running. Does that indicate there is a problem, perhaps with the rad? Perhaps it is clogged with rust, inhibiting its ability to dissipate heat?

I totally agree with the principle of "if it ain't broke...", however, because of the age of the rad, I would like to prevent any issues before they occur. The fan never cycling off while the engine is idling seems like a red flag. If so, I will accelerate my plan for replacement. We bought the car in October and have not yet driven it in hot weather. The fan never cycling off in the cool garage gives me trepidation about doing so.

I was looking at Autoricambi's rads and low-temp t-stat, but I'm kind of at a loss as to the advantage of a t-stat that opens at a temperature lower than normal operating temperature. Isn't the idea for the engine to get to operating temperature and then redirect coolant to the rad?

So, I have two questions: One diagnostic and one conceptual.

[v6spider]

Lowering the temp rating of the thermostat increases coolant flow through the radiator thus lowering the operating temperature. If you live in a warm location I would run the lower temp rated thermostat. My spider is heavily modified. I run a 160° thermostat with four 1/8" holes in flange. This increases for even more. Btw just because the thermostat is rated at a certain temperature doesn't mean it will run normally at that temp. That is where the thermostat is rated to open. In my cooling system it will run down the road at 50mph at 180° but it will creep up to 190°f .. Then the fans kicks in and cools it to 185°. Like Matt stated burping the air out of the system is crucial to your cooling system working properly. When it is cold jack up the front of the car so that the top of the radiator is higher than the top of the engine. Take off the radiator cap and start the engine this will force any air present in the engine into the radiator of the cooling system. Keep topping it off with coolant until the radiator is full. Then put on the cap and fill the coolant overflow tank to the full or max mark. Run the engine until it reaches opperating temp. And then shut it down. Allow it to cool. Then lower the car.. Check the level of the overflow tank and top off if needed. This should burp the air out.. At that point you can run the car and see if it exhibits the fan issue.

Hope this helps!

Rob

[So Cal Mark]

my experience has been that if the fan can't lower the temp and cycle off, the radiator is partially plugged

[baltobernie]

Isn't the idea for the engine to get to operating temperature and then redirect coolant to the rad?

Yes. Particularly with fuel injection, the engine has an ideal operating range calculated by the designer. Obviously, if you have extensively modified your engine, then you must also modify other components of the power train ... including the cooling system. But you will never experience ambient temperatures in New Jersey that a well-performing stock cooling system can't handle in a stock or nearly-stock Spider. I have inched along I-95 in 100°F ambient for 90 minutes without the coolant exceeding 220°. The car had greater stamina than I

A $20 infrared thermometer can tell you if your radiator is performing satisfactorily. (It can also tell you if one of your calipers is dragging, or if one of your wheel bearings is cooked)

[v6spider]

my experience has been that if the fan can't lower the temp and cycle off, the radiator is partially plugged

Good call Mark!

Rob

[KevAndAndi]

Thanks, all; very helpful. As the rad & fan seem to be straining to stay cool (though I haven't seen any overheating yet), rad plugging was what I suspected, but I wanted to hear from the experts here first. If I was looking for an excuse to get a new rad, I think I have it.

As an aside to Mark, last night I received the shipment with the Big Brake kit along with the SS heater pipe and billet aluminum throttle body heater - thanks. I was on the fence about that throttle body heater, but not that I see how it's going to look on the car, I know I made the right decision. The TBH is a central focus of the engine, appearance-wise, and having a shiny, polished one improves hugely over my old, corroded one. Plus, the bleed screw should help to get air out of the system - I think even my Prestone T is lower than the TBH.

Last question: Would a low-temp t-stat lower the temp of the exhaust manifold at all? There are no shields in that area and I'm concerned about the air intake, AFM, dizzy, etc. which get quite hot.

[amawds]

No, a low temp t-stat will not lower your header temperature. I've been running for three years with a steel header and have had absolutely no issues. That could change with time. Who knows.

I'm going to be a devils advocate and remind people that engines are designed with a certain temperature in mind, and lowering the temperature actually makes them LESS efficient. Newer engines run hotter with higher pressure radiator caps in search of perfect combustion. There's absolutely no reason to go backwards. If you have a heavily modified engine on a race track and you have heat issues, the thermostat is already wide open. Opening it earlier is going to do nothing but slightly delay an overheat. Your radiator is not up for the task at that point. Keep the stock t-stat.

I will say the low temp fan thermoswitch was a good buy for me because it keeps the temperature from reaching three quarters of the gauge before flicking the fan on. Now I can leave it idling all day and the gauge only moves around about a mm back and forth right in the middle of the gauge.

[KevAndAndi]

Thanks, amadws, I appreciate getting all perspectives.

Did you install the fan thermoswitch that is adjustable? It does seem beneficial to be able to tweak the temp at which the fan comes on.

[So Cal Mark]

well, yes engines are designed for a specific temperature range but what the really like is a constant temp, not up and down fluctuations. If you remember the 70s, emission reduction became the focal point and the big effort was to reduce hydrocarbons. The mfgs found they could accomplish that by raising the engine temperature. Running leaner mixtures and high engine temps did reduce HC drastically. But a new, less healthy of this change was Nox. While lean mixtures and high engine temps helped with HC reduction, Nox levels went through the roof. Nox was never an issue until mixtures were leaned out. So, putting that 195F thermostat in created a whole new issue.
Your engine will be quite happy with a 175 thermostat, as I said, the important thing is a constant temperature. You would have to experience engine temps below 160F to consider temperature as a detriment.
Actual engine temp will average about 20 degrees hotter than the thermostat rating

[amawds]

Thanks, amadws, I appreciate getting all perspectives.

Did you install the fan thermoswitch that is adjustable? It does seem beneficial to be able to tweak the temp at which the fan comes on.

No, I didn't install the adjustable thermoswitch, I purchased the low temp variant from autoricambi.

Mark while I agree it's more important to hold a constant temperature, I still fail to see reason to drop engine temperatures when there's evidence that it'll decrease performance and efficiency.

[KevAndAndi]

Well, we took the car out last night. I had set a Mother's Day deadline for getting my wife's Spider at least running well enough to take it for a couple-mile spin. In addition to working on the air intake and replacing vacuum hoses with blue silicone ones, I had to address the crumbling brake fluid reservoir and rotting hoses which were starting to leak around the master cylinder. Got the new reservoir and its hoses from Autoricambi installed. The new vacuum hose on the brake booster (which was rebuilt by the PO's mechanic, who then went ahead and reinstalled the original, cracked, rotting vacuum hose) appeared to be working. When I started the engine with my foot on the brake pedal, I could feel the vacuum pull. So far, so good.

Pulled the car's owner off the couch, put some Beatles on the stereo, and took the Spider for a quick run in the dark with feeble headlights. Temperature while idling got up into 200 territory, which I hadn't seen before. Temp while driving then dropped well below 190. I suspected that the cooling fan was continuously running (despite the somewhat cool evening) because that's what it's been doing lately. Parked the car in the garage. Fan kept running, which is normal. Made mental note to come back and check it. Sure enough, it was still running long after the engine had cooled down. Unplugged the fan to prevent it from running down the battery. Ordered a new thermoswitch from Autoricambi.

I guess the earlier continuous, no-cycling-off, running of the fan (that occurred only while the engine was running or when the engine was cooling down) was a precursor to the thermoswitch failing entirely and causing continuous running no matter what the temperature.