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I've been remote tuning this week a customer's 3900 with HPTuners and once again I've run into a 3500/3900 that is running very hot that the owner previously didn't know. The temperature gauge on the dash really is a dummy gauge, you won't see a difference between running at 200*F coolant temp or 215-220*F, which is where his vehicle is running.
This is not uncommon, I've consistently seen this issue on 3500/3900s, including my father in law's brand-new-at-the-time 2010 3500 Impala. When the engine runs this hot, performance suffers due to spark knock retard, and it'll bring up some engine longevity issues, especially if you're not running synthetic oil and/or not changing your oil often enough.
My attention once again turns to the thermostat. The factory 3500/3900 is a 187* opening temperature thermostat. I'm not convinced its doing its job, simply because its the thermostat's job to regulate the temps. My main concern is the factory thermostat is a bottom bypass unit. What this means is there's a flapper valve on the bottom of the unit. It's meant to block off the coolant flow from recirculating in the block once the thermostat opens, forcing flow through the radiator and not allowing any natural recirculation. A traditional thermostat will allow cooled coolant to join the normal circulation of coolant when the thermostat opens, rather than trying to force a bypass flow. I don't know for sure if there's a flow issue that's created, but I do wonder.
I purchased a boatload of thermostats to find an alternative, and here's what I found...
The 3800 thermostat flange is a direct fit, its the same diameter, its basically the 3900 thermostat without the bypass flapper at the bottom. The 3800 seal is close in size too but the 3500/3900 seal fits the 3800 stat. The 3800 thermostat is a non-bypass, so it will open and allow coolant flow through the radiator, but won't obstruct coolant flow. It's available in a high flow unit if you get the right part number. Its also available in 160*, 180* and 195*, of which I think we should look at trying the 180* high flow unit, which is available from Motorad using part number 2003-180 (note that similar part number 203-180 is the non-high-flow unit, don't get them mixed up).
So here's the deal, I don't have a 3500/3900 vehicle to test this on, so I'm calling on the community to take over from here. Someone should try installing this thermostat, and in particular someone who has access to a scan tool to monitor coolant temperatures and do a real before and after comparison.
Again, Motorad part number 2003-180 gets you the HIGH FLOW 180* thermostat, and Felpro 35614 gets you a new 3500/3900 seal. This thermostat will be a direct swap for the factory thermostat.
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This is not uncommon, I've consistently seen this issue on 3500/3900s, including my father in law's brand-new-at-the-time 2010 3500 Impala. When the engine runs this hot, performance suffers due to spark knock retard, and it'll bring up some engine longevity issues, especially if you're not running synthetic oil and/or not changing your oil often enough.
My attention once again turns to the thermostat. The factory 3500/3900 is a 187* opening temperature thermostat. I'm not convinced its doing its job, simply because its the thermostat's job to regulate the temps. My main concern is the factory thermostat is a bottom bypass unit. What this means is there's a flapper valve on the bottom of the unit. It's meant to block off the coolant flow from recirculating in the block once the thermostat opens, forcing flow through the radiator and not allowing any natural recirculation. A traditional thermostat will allow cooled coolant to join the normal circulation of coolant when the thermostat opens, rather than trying to force a bypass flow. I don't know for sure if there's a flow issue that's created, but I do wonder.
I purchased a boatload of thermostats to find an alternative, and here's what I found...
The 3800 thermostat flange is a direct fit, its the same diameter, its basically the 3900 thermostat without the bypass flapper at the bottom. The 3800 seal is close in size too but the 3500/3900 seal fits the 3800 stat. The 3800 thermostat is a non-bypass, so it will open and allow coolant flow through the radiator, but won't obstruct coolant flow. It's available in a high flow unit if you get the right part number. Its also available in 160*, 180* and 195*, of which I think we should look at trying the 180* high flow unit, which is available from Motorad using part number 2003-180 (note that similar part number 203-180 is the non-high-flow unit, don't get them mixed up).
So here's the deal, I don't have a 3500/3900 vehicle to test this on, so I'm calling on the community to take over from here. Someone should try installing this thermostat, and in particular someone who has access to a scan tool to monitor coolant temperatures and do a real before and after comparison.
Again, Motorad part number 2003-180 gets you the HIGH FLOW 180* thermostat, and Felpro 35614 gets you a new 3500/3900 seal. This thermostat will be a direct swap for the factory thermostat.
