When running an in-head thermostat, use a 160F thermostat

[ebrown0104]

I recently had to remove my radiator to have the cracked filler neck replaced, and while it was out I decided to replace the hoses since they are of an indeterminate age. I converted to the early-style system (I have a 77) with the thermostat in the cylinder head, mainly because I like how it looks better and a replacement thermostat can be obtained at any auto parts store for $7. So I put in the 180-degree thermostat, hooked everything up, filled it with antifreeze, and went for a drive. Here's where my issue started...

The car never overheated, but it would run really hot. Like 230-240 hot. Just below the red zone on the gauge. It would occasionally drop to 200-210 for a few seconds, but was normally up near the limit. If you turned on the heater it would help keep the temp lower, but while that's fine on a cool fall morning it's not gonna work in July when it's 90 degress outside. I also noticed that even though the temperature gauge was reading high, the fan wouldn't kick on unless it sat idling for a while, and the lower rad hose was always fairly cool. From this, I gathered that while the coolant in the cylinder head/heater core was getting really hot, the thermostat wasn't heating up enough to open and flow through the radiator (assuming it's because of the lack of circulation of the old-style system).

I put in a 160-degree thermostat, and now it's back at 190 exactly on the temp gauge.

So here's my advice to anyone converting to the old-style cooling system - use a 160 thermostat from the start. It seems like it's too low of a temp for a car that originally used a 195-degree thermostat, but it works. Hopefully this saves someone some frustration (and possibly a warped head) later on.

[So Cal Mark]

now that you're eliminated the external thermostat that featured a bypass circuit so that water circulated through the block with the stat closed, how did you incorporate a bypass circuit? T-stats are constantly in motion, opening/closing to regulate the temperature. Without a bypass circuit you stand the chance of having extreme hot spots in the block when the stat is closed or partially closed

[vandor]

Actually this is not an uncommon problem when a later engine is converted to an in-head t-stat. The original type water pump seems to be prone to cavitating when water flow is completely shut off by the thermostat. Likely this is why Fiat went with the external design.
Usually the symptom is overheating during steady engine speed, like highway driving. Varying engine speed, like city driving, usually lessens the problem.
The GMB water pumps have a different impeller design and they do not cavitate under these conditions.

[So Cal Mark]

the external stats flow more than the in-head stats, a requirement as the engine displacement increased

[bradartigue]

I've always considered this "upgrade" to be asking for trouble. You can go back 14, 15, 20 years on mirafiori.com and find archives of people switching to and then back, for example:

http://archive.mirafiori.com/show.php?fid=2&msg=72071

I'm not sure what issue people are trying to solve with this internal thermostat, particularly on engines made after 1970, when the design was for an external type only.

[v6spider]

now that you're eliminated the external thermostat that featured a bypass circuit so that water circulated through the block with the stat closed, how did you incorporate a bypass circuit? T-stats are constantly in motion, opening/closing to regulate the temperature. Without a bypass circuit you stand the chance of having extreme hot spots in the block when the stat is closed or partially closed

That certainly would be a problem. Most engines that feature a block mounted thermostat that I've dealt with have a bypass port in the block that goes into the water pump.. However, you could drill four ⅛" holes in the thermostat flange that would help with the lack of a bypass.. The external system sounds like it was an improvement over the earlier design. Usually when making that kind of modification its covering up another problem like a clogged radiator or air in the in cooling system.

Cheers!
Rob

[ebrown0104]

I'm not saying that the conversion is a good or bad idea, but I do know that at least a few other people have done it to their cars. I still have my original water neck and t-stat to switch back if I ever have an issue. Truthfully, I just like how the in-head setup looks better, and since I needed new radiator hoses anyway I just found a cheap old-style water neck and went for it.

As far as circulation goes, I figure that keeping the heater core valve open halfway should let enough water circulate to keep hot spots from forming. Do the older engines have something different from the newer ones that would let water circulate internally?

[bradartigue]

Liking how something looks isn't a very good justification for altering an important system. This modification is similar to blocking off an oil gallery. You can do it, and it likely won't have a short term effect, but the cumulative problem may be quite large.

[v6spider]

I'm not saying that the conversion is a good or bad idea, but I do know that at least a few other people have done it to their cars. I still have my original water neck and t-stat to switch back if I ever have an issue. Truthfully, I just like how the in-head setup looks better, and since I needed new radiator hoses anyway I just found a cheap old-style water neck and went for it.

As far as circulation goes, I figure that keeping the heater core valve open halfway should let enough water circulate to keep hot spots from forming. Do the older engines have something different from the newer ones that would let water circulate internally?

Yes they do...

[Turbofiat124]

Years ago my 68 Ford Fairlane 302 would run 30 degrees hotter than what ever thermostat was in the engine. With a 190F thermostat, the engine would start to run hot at idle (230F). So in order for the engine to operate at 190F, I had to run a 160F thermostat.

Fast forward a few years. Eventually my radiator rotted to the point it was spraying from several pinhole leaks in the tubes. So I replaced the radiator with a new one then discovered my engine ran cooler than normal. Now I have a 190F thermostat and the engine runs at 190F even in the middle of summer. This is with a mechanical fan bolted directly to the water pump.

I'll have to agree about the in-head thermostats. This is the ONLY car I have ever owned with such a finicky cooling system. Usually it involves the electric fan not kicking on when it should (like 235F) and allot of times simply replacing a radiator cap fixes the problem. My 1998 Chevy van as 140,000 miles on it with the original radiator cap. I bet I've replaced 5 radiator caps on my Spider since 1998. I stopped using those Stant 13 lb caps years ago.

I have never seen a car with such a temperamental cooling system. Prone to air locks when refilling. Or you may get the air out of the system the first time but the next time you start the engine, the overflow tank boils over. So I'm thinking if it's working OK now why make it worse?

I think if it were not for the fact that the head is higher than the radiator, the external thermostat system would probably not be necessary. I think that is one reason they went to it.

Also the radiator on a Spider is rather large for a 2 liter engine. The radiator on my 2.5 Subaru is about half as thick.

I have thought about going to the in-head thermostat but not for cost savings or simplicity reasons but to gain space in the engine compartment for other things. Like my turbo system and air conditioning system. I had to shorten some of the hoses by an inch to clear the air flow meter. As you can see the lower hose barely clears the black cap on the AFM. The AFM takes up allot of space itself.

[bradartigue]

It was implemented with the 1438cc motors, which didn't have as big an issue with the radiator height (the motor was quite a bit shorter than the 1800 and 2000). This was a universal change to all 124 series vehicles in the late 1960s, it wasn't Spider-specific.

Quoting the old (66-70) shop manual for the 124 series:

Up to engine No. 176.338, to equalize the cooling
water temperature during warming up, a thermostat
has been fitted in the water outlet on cylinder head
to the radiator.

Other modifications include cylinder head changes - primarily a water outlet added to the rear of the head - and a new intake manifold that allowed circulation throughout the head (vs. just a single outlet and circulation by heat exchange alone). Again, this was a series-wide change, affecting twin and single cam engines on every variant of the car. It remained the case throughout production of the 132 series motors (Spider 2000 being the last 124 series).

[v6spider]

It was implemented with the 1438cc motors, which didn't have as big an issue with the radiator height (the motor was quite a bit shorter than the 1800 and 2000). This was a universal change to all 124 series vehicles in the late 1960's ...

Radiator being lower than the heads in my v6spider had been an issue as well.. They make filler cap setup that mounts on the intake manifold where the thermostat is housed. I will be upgrading to that.. I have to jack the front of the car up in order to burp the air out of the cooling system as it is now..

Cheers!
Rob