jeeptec1 Posted June 26, 2021 Share Posted June 26, 2021 88 Comanche 4.0 automatic. So climbing our somewhat famous Cuesta grade 5 miles up to 7% grade Comanche got warm. Bottom of grade 70 degrees. Top of grade 100 degrees. Comanche hit 220 which is odd for my truck. Then came down and stayed 215. Got of hiway temp dropped running in town to about 200. Electric aux fan is pulling strong air, fan clutch engaged and pulling strong. Coolant bottle has plenty of coolant. No water in oil and vise versus. Everything is pointing towards Radiator time. I had similar issues on a 87 Cherokee. On my 87 Cherokee I installed a 91 and later radiator. Dumped the coolant bottle but can’t remember if I just bypassed the bottle or installed a 91 later heater valve. Note my electric aux fan comes on with a/c on and using a temp switch installed on the 91 later thermostat housing. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
ghetdjc320 Posted June 27, 2021 Share Posted June 27, 2021 Have you tried doing a good coolant flush? Link to comment Share on other sites More sharing options...
Pete M Posted June 27, 2021 Share Posted June 27, 2021 220 is nothing all that out of the ordinary for a particularly stressful drive in a renix Jeep. also be aware that the dash gauge is not all that accurate. Link to comment Share on other sites More sharing options...
Minuit Posted June 27, 2021 Share Posted June 27, 2021 My point of view: The factory gauge is only trustworthy if your electrical connections are in good shape and if the sensor is a genuine Mopar product. If both of those are true, and maybe you've double checked it against an infrared thermometer, I would consider it a valid source of information. If you haven't changed the coolant in the last couple of years or so, do it. If the coolant is dirty, keep flushing it until it's clean. Regular coolant flushes prevent so many problems. The A/C puts a considerable extra heat load on the system. Your truck is also an automatic, which puts even more heat load on the system. Climbing a hill when it's hot outside, in an automatic truck, with the A/C on is literally the worst case scenario for the cooling system. If your gauge is telling the truth, I don't think you have any huge problem going on - especially if you have the puny stock radiator still. If you want to bring the temps down, look into a good coolant flush, or maybe one of the larger radiators on the market. I have the CSF 3-row, but there are plenty of options. I personally like my factory gauge to cover up the "2" in "210" once warmed up and stay there. That means the thermostat is regulating the temperature at 195, and the cooling system has excess capacity to remove heat in case it's needed. That doesn't necessarily mean any temperature over 195 is bad for the engine, but if the thermostat is no longer in control, you are in danger of running warm if you run the engine hard or are sitting in traffic on a hot day. Here's my cooling system "recipe" that I think could handle just about anything that most people could throw at it: - Standard '91 open cooling system - CSF 2671 3-row radiator - 97+ auxiliary fan (simple connector swap required for fan to plug into truck - will also improve A/C performance at low speed) - Hayden 678 transmission cooler - Stock replacement fan clutch - 50/50 bulk green coolant and distilled water. I don't use any additives. Link to comment Share on other sites More sharing options...
jeeptec1 Posted June 27, 2021 Author Share Posted June 27, 2021 Some good info everyone has posted. My aux cooling fan is a 97 R134 fan I installed. I replaced the fan and fan clutch last year all at the same time. The previous owner did replace the radiator with a parts store single core radiator. My past experience with both MJ and XJ is they like 2 or 3 core radiators. Also I’ve found is that the Renix engine have boil issue’s in the rail when you run them hot. I found on my 89 MJ and 87 XJ they liked the the 2-3 core 91 and later radiator conversion. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
cruiser54 Posted June 27, 2021 Share Posted June 27, 2021 70 and 100 at the bottom of the grade? That truck even have a thermostat in it? Link to comment Share on other sites More sharing options...
jeeptec1 Posted June 27, 2021 Author Share Posted June 27, 2021 70 and 100 at the bottom of the grade? That truck even have a thermostat in it? That was the outside temp. The truck was at 190 at the bottom of the grade 220 at the top. I drove the truck to the hardware store this morning. It acted like the thermostat is now stock open. Never fully warmed up. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
cruiser54 Posted June 27, 2021 Share Posted June 27, 2021 Get a Mopar stat. Flush the system while you're at it. Original radiator? Best to check temp with an IR tool at the thermostat housing. Link to comment Share on other sites More sharing options...
JMO413 Posted June 27, 2021 Share Posted June 27, 2021 1 hour ago, cruiser54 said: Get a Mopar stat. Flush the system while you're at it. Original radiator? Best to check temp with an IR tool at the thermostat housing. I would also check you radiator hoses. Old rubber likes to collapse. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted June 27, 2021 Share Posted June 27, 2021 I’ve ordered a couple of Mopar thermostat recently. The first was a Mopar with the little vent in the theromostat to purge air from the system. The other was in a Mopar package with part number but was a plain Stat thermostat. Link to comment Share on other sites More sharing options...
jeeptec1 Posted July 2, 2021 Author Share Posted July 2, 2021 Took my cooling system apart. Found the thermostat stuck open about 1/8 inch. Coolant looked green but back flushing the block got rust coming out. I took and back flushed the radiator and got quite bit of black flake like rust out of the radiator. I bought the truck 2 years ago. The guy I bought it from rescued it after sitting 15 plus years. Put a radiator in it etc. I put a water pump in it last year. Back flushed it then. Years of sitting has created a bunch of rust that keeps loosing up. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Pete M Posted July 2, 2021 Share Posted July 2, 2021 yeah, Jeeps don't like to sit. Link to comment Share on other sites More sharing options...
PCO6 Posted July 2, 2021 Share Posted July 2, 2021 On 6/27/2021 at 1:22 PM, cruiser54 said: 70 and 100 at the bottom of the grade? That truck even have a thermostat in it? Mine runs at "100" all the time! It's metric and the gauge reads 40/100/125 *C. Link to comment Share on other sites More sharing options...
jeeptec1 Posted July 2, 2021 Author Share Posted July 2, 2021 Mine runs at "100" all the time! It's metric and the gauge reads 40/100/125 *C. That is the outside ambient temperature. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
cruiser54 Posted July 2, 2021 Share Posted July 2, 2021 Mumblemeters on a temp gauge....... Link to comment Share on other sites More sharing options...
PCO6 Posted July 2, 2021 Share Posted July 2, 2021 1 hour ago, jeeptec1 said: That is the outside ambient temperature. Sent from my iPhone using Tapatalk ... I was pulling legs. Link to comment Share on other sites More sharing options...
PCO6 Posted July 2, 2021 Share Posted July 2, 2021 1 hour ago, cruiser54 said: Mumblemeters on a temp gauge....... I agree! I started "real" working the early '70s when the metric system became official in Canada. We weren't taught any of it in school prior to that, not that it's all that hard. Many of us relied on conversion rather than thinking things through in metric. A lot of us still do. In my line of work (now retired) I had to present land development applications to municipal employees and councils, ratepayer groups, etc. I often told them that ... "my decision on whether to use imperial or metric measurements was solely based on the age of the person I was trying to confuse." I wasn't always kidding! btw - Our speedometers had both for for many years. Glad they finally got rid of that. Link to comment Share on other sites More sharing options...
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