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Old 06-28-2016
NLBurden's Avatar
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Engine temperature spike

Hi guys quick question. I have a 03 Ranger 4.0. Runs strong, however I have a strange potential issue. After I cold start my truck she runs good and normal, however as she continues to warm up to operating temperature she eventually spikes on the temperature gauge. I will watch the temperature slowly climb, then it will sit near " high " on the gauge. Maybe 3/4 up the temperature gauge. After about a minute it will go back down to normal operating temperature and remain there. Only happens after a cold start.

Does it sound like a thermostat going bad?
Has this happened to other rangers? (common problem )
Could it be a water pump going?

* Truck does not make any weird noises or rattles. As well it doesnt seem low on coolant and it doesn't leak.

Thanks for any input!
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Old 06-28-2016
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It is the thermostat opening, so you are correct.

Really depends on driving conditions to tell if it is normal.

When I leave my house I have to go up a longer grade on the highway after about 4 or 5 minutes of driving.
If there is traffic, so it takes longer to get on the highway, then thermostat is just opening at the top of the grade so temp will go up to about 3/4 on the gauge and then drop back down.
If there is no traffic and I get over the grade faster then temp will go up just over 1/2 then drop when thermostat opens.

After thermostat is open for awhile temp gauge runs just under 1/2, but will climb to 1/2 on longer uphill grades

Been that way for years.
If it was doing it on flat roads then I might change thermostat, really up to you

Good read here on changing thermostat on the 4.0l SOHC: How To Replace the Upper and Lower Thermostat Housing on a Ford 4.0L V6 SOHC Engine
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