Temp raises and then drops, thought it was a thermostat, but...

Couple of thoughts...

Does this temp variation happen while cruising down the road or does the temp stay "normal" in those conditions? If OK running down the road but not at low speed, could be the radiator fans are not activating when they should. Could also be low coolant level/air in the system. Did/does the car routinely "spit" coolant from the expansion tank overflow?

I'd check the temps at the top of the radiator box with an IR gun to see if the temp readings there correspond in relative terms with what the temp gauge shows when its reading high and low. Don't worry about the specific readings, just determine if the same relative variation exists. That will identify that the gauge/sender is working OK (or not). If those readings correlate, I'd then make the same check between the Tstat box and the top of the radiator, again, looking for correlation between the high/low readings. If those readings don't correlate, air in the system/low coolant level could be the problem.

If there is air in the system you need to consider WHY there is air in the system. If the system is properly filled/bled and is in good condition with the correct type of radiator cap, it does not "create" air. Air gets into the system because something is leaking/not functioning properly. As you have probably seen on other posts, there are a two basic different types of radiator caps. One has the little disc (return valve) on the bottom side of the cap hanging down (open); the other type has that disc lightly spring-loaded shut. You need the one with the disc spring-loaded shut. Check yours to be sure you have the correct type.

There are serious issues that can cause the symptoms but first I'd check the above.

Good Luck!

 

Have you tried bleeding the system? If so, did you get a bunch of air out of it?

 

Sticky thermostat, mine did this and was cured with a new stat. Make sure you get the right one as there are a lot for sale that are not suitable. Make sure it has the rubber seal on the primary disc. If it doesn't it will not seal correctly and water will short circuit around the engine block showing higher temps.

See Birdmans page on 308 cooling
http://birdman308.com/service/coolant/coolant_troubleshoot.htm

 

Air in the system that does not get expunged through the bleed hose to the expansion tank will eventually make it's way to the radiator and get trapped at the top. so a simple way to find out is just open the radiator bleed screw and see how much air is in there. If you have a drilled bleed screw you can carefully do this when it's warm but otherwise you'll need to open the cap on the expansion tank when it's cool and have it at least half full to bleed the air out. Having the nose of the car a bit lower will help as well. If, after bleeding, the symptom continues you'll have to find out where the air is getting in. Addressing a leak in your radiator is a good place to start.

 

As I mentioned earlier, check the expansion tank cap to be sure it is the correct type - with the little brass disc on the underside spring-loaded shut. The wrong type cap can cause the problem you are experiencing. The type that the disc hangs open is NOT for expansion tank systems like the 3x8; it is for systems with overflow tanks/bottles.

 

This is a highly talked about subject here on Ferrari Chat. I have read about having bad caps, thermostat's, water pumps, expansion tanks, leaking hoses, radiators, leaking head gaskets and more. Which one's do you have? In my experience you want to find out also when is the air entering the system. By this I mean, does the air enter the system when the car is cooling down or heating up. As the cooling system is cooling down it puts a vacuum on the system, it could be pulling air in from a bad seal connection or most common problem is the radiator cap. First when bleeding the system you may have to bleed it many times. Don't forget to bleed the air out using the bleed screw on top of the thermostat. You also need to open the heater valves to let the air out of the heater cores and hoses. Or is air entering the system when the car is running. After bleeding the system many times take the car for a nice drive and when the car is hot open the bleed screw at the radiator very carefully not to get burnt and see if there is any air in the system. If you are getting air in the system as the car is heating up you may have a more serious problem. Do a block test to check for a leaking head gasket. I always see lots of suggestion but not many people report back that they really fixed the problem and what the problem was. Let us know what you found to fix the problem. Just my thoughts. Does some have pictures of the right and wrong radiator caps? Thanks Dave

 

I had this problem, same symptom of the temp gauge rapidly rising and then dropping and air in the radiator. In my case it was a head gasket, when I did a leak down test on all cylinders I could hear it gurgling on #4. Not saying this is your problem just that if it persists and you can’t get it bled out you need to investigate further. In my experience the block test is not reliably conclusive, I kept getting negative results even though I could see a constant stream of air bubbles entering the expansion tank through the bleed hose.

 

The temp change as the PO described IS a classic symptom of a blown head gasket but it could be, and hopefully is, something less than that. As noted, checking for a head gasket blown to the water jacket is fairly pain-free with analyzers that can check the radiator "fumes" for exhaust gas. Such a test is the quickest way to rule out ...or confirm ... that issue.

Re pics of the correct type of rad cap - someone posted those pics here a while back so I know they are here...somewhere. BUT one way to ensure you have the correct type is to simply order it from Ricambi as opposed to hoping you selected the proper one from the local parts store. I made that error - bought the one that was listed as fitting a '89 328 Ferrari from the local parts store. Of course, it fit just fine; it just didn't work correctly and I later discovered that the system didn't pressurize. During that time I was slowly losing coolant and, after the coolant level dropped far enough in the expansion tank, sucking air into the system when the car cooled. It was the sudden temp change that occurred one day that started me on the road to figuring out the cause, which included doing the head gasket check. But it was simply the wrong rad cap. I realize you can buy a rad cap much cheaper from Pep Boys (or whoever) but IMO, it's better to pay more to ensure you have the right one for the system.

 

As I mentioned in the last post you can start the engine cold with the expansion tank cap removed and look inside with a flashlight. When the thermostat is closed the coolant simply circulates through the engine and any trapped air gets pushed out through the bleed hose at the top of the coolant manifold between the heads and can be seen as bubbles flowing into the expansion tank. If you see a constant stream of bubbles then you've got a problem. If not then just keep bleeding the radiator until the symptom ends and may as well get a new cap (making sure you have the correct one) while you're at it. I got a correct one from Superformance.
I don't want to alarm you, the symptom can be caused by numerous things, doesn't necessarily mean you have a blown head gasket.

 

That is a great write up by birdman, this is why I enjoy Fchat so much, help and understanding stuff is just a click away on here.

Question though, what is the correct replacement thermostat in a 328 euro 1989??
54mm or 56mm wahler/stant or Behr

 

many causes are possible, here you are some: (from most probable to less probable)

1) blown head gasket (my pick)
2) a small pore (or porosity) in one head: you need a new head
3) a lot of dirty in the cooling system
4) air in the cooling system
5) bad water pump and water pump belt at the end of its life

good luck!

ciao

 

Paul, where does the constant stream of bubbles come from?

 

Paul - sorry I don't know. Try their technical department for advice.

 

In my case #4 cylinder. After removing the head I could clearly see the breach point between cylinder and coolant passage as well as the clean section of the piston head.

 

I had this exact same issue with my 308. in the end the best thing to do, is pull the radiator - and have it re cored. when I did that ( the car was down for major service ) the rad shop told me when they tested the radiator under pressure there was tons of small hair line cracks and leaks that made it like a sauna ... not enough at once to make a leak that you could see - but you could sometime smell some coolant ... regardless the gauge would ping up and down when it was truly hot in city driving.
so they put a new core in , and had room to fit two extra rows of tubes... and it helped a lot. when I got the car running again I drove it for an hour - lots of idling , and then just left the car running fans on and the temp gauge just sat at about 120, steady ... which for me in Atlanta was IMPRESSIVE...

so assuming your pump and hoses are solid, I think you can be getting air in from these hairline cracks ... my rad was original and as usual was poorly assembled with Italian welds etc... I think the total cost ( 15 years ago ) was $400. I wished I had done it 10 years earlier.

 

To clarify my own experience: I would start the car cold and after a few minutes the low temp light would extinguish and the fast idle would drop to normal. I would begin driving and the temp gauge would quickly rise to well past the 190 point yet the heater would be blowing cold air. It would then, just as quickly drop back down to just below the 1/4 point which is where it should have been and slowly rise back up to normal at which point the heater also worked normal. So long as I was moving it would be okay but if I got caught in traffic the fans were not able to contain it and the temp would continue to slowly rise. At times it would spit coolant out through the overflow hose and I was always bleeding air out of the radiator. So I started with a new cap, then a new thermostat, all new hoses, a new radiator and finally a new water pump. Each gave me a little improvement but did not solve the underlying problem which always returned eventually. Upon further investigation, doing a leak down test of each cylinder, I found the head gasket leak on #4. I had been observing the stream of air bubbles into the expansion tank from the beginning and it had continued to concern and perplex me. I have it all back together now and there are no bubbles.

So my suggestion is to follow the same path and start with the simplest and least expensive component - the cap. There are plenty of similar threads where that was all it took.

 

This was happening on my car and it turned out to be a wonky gauge. Have you tried tapping on the glass when it peaks high? An IR temp gun aimed at the thermostat housing confirmed the gauge was off...