help please truck with little heat when temp below 20ｰ F

[diesel lover]

I have a 1997 f150 with a 4.2 V6. The heat supplied is low when under 20 degrees. As soon as I start to idle I believe the coolant temp cools down. Also it may start hot and then cool down going down the road. I have my blend door stuck open to the heat position. I manually did this.

If I run the truck with overdrive off (direct drive) than I have okay heat. If I run it with overdrive colder heat is received. Like I said when idling the heat temp received out of the vents gets lower. I believe my truck needs a thermostat. It does run cold. I have repairs to complete once it warms up outside and a thermostat will be one of them. These week its going to be near 0 and -15F without a garage I can't complete any repairs.


Here's the question I have cardboard in the front and It is helping. I believe my transmission cooler is inside the radiator. Am I doing any harm at all by using the card board? Am I raising the transmission temperature to unheslthy levels? I never ever have hard to do this. I dong use the cardboard unless below 20ｰ its removed when warmer.

 

[Diamondpilot]

The thermostat is the issue. Not sure on the 4.2 but many Ford's have 2. It's called rapid heat or something like that. What it does is takes the radiator out of the equation till a certain temp. The idea is to give you heat quicker by circulating only 1/3 of the coolant.

Chris

 

[diesel lover]

The thermostat is the issue. Not sure on the 4.2 but many Ford's have 2. It's called rapid heat or something like that. What it does is takes the radiator out of the equation till a certain temp. The idea is to give you heat quicker by circulating only 1/3 of the coolant.

Chris

Yes sir! Thanks for the explanation. The heat according to the temp gauge runs just over a quarter. I measured the temperature on the thermostat housing but can't recall what it was. I have a laser temperature gun I used in warmer weather. I do have a code reader. Let me plug it in and find out what the temp reads on there.

So the main question was will the cardboard over my grill cause any issues? Could it raise my trans temp to unsafe levels?

 

[tcartwri]

No problem.

Actually running around with a cold engine is more of a concern. It builds a ton of condensation in the crankcase.

 

[diesel lover]

Yes! I do not like running cold engines. I have a freeze plug mounted block heater I run when weather dips under 10°F. Makes a large difference on fuel usage not to mention how much better it starts. The engine runs a lot better when the block Heater is plugged in. The difference is mostly noted when the temperature falls down to -14 F ambient . Engines are designed to run more rich when cold. A bad thermostat or a engine that normally runs cold can use considerably more fuel! Once the ecm reads the coolant temp it can decide what fuel mixture to use

 

[diesel lover]

The worry with the transmission temp was due to the fact with external transmission coolers. External coolers will heat up rapidly with a piece of cardboard in front of them. Did not know if it effected coolers inside the radiator.

Thank you guys at TBN

 

[tcartwri]

You should also check your coolant level! If it's low enough the temp sender may be uncovered and giving you false cool readings, and will also give you no heat as the air lock tends to settle in the heater core.

 

[diesel lover]

You should also check your coolant level! If it's low enough the temp sender may be uncovered and giving you false cool readings, and will also give you no heat as the air lock tends to settle in the heater core.

Not a problem. I check my coolant level between once a day and once every other day worst case. I'm proud to say I keep my engine oil full and when its half a quart low I add half a quart but never overfill. I keep my fluids taken care of, keep my tires full and my truck takes care of me

 

[Diamondpilot]

I would remove the cardboard if I was working the truck. Like you said it could create a tranny issue.

Chris

 

[JoeL4330]

If I understand the OP initial question, the answer is "no problem" assuming that both your engine coolant and transmission fluid are circulating properly. ...the transmission cooler inside the radiator exchanges heat with the water in the radiator and, therefore, the transmission fluid (at the output of the cooler) is pretty much the same as the coolant temp in the radiator, which you know is below its boiling-over point.

The fact that you get more heat at the heater outlet when the transmission is "working harder" seems to indicate that your coolant is being warmed disproportionately by the transmission, rather than by engine temp ...which suggests engine is not coming up to proper operating temp, which suggests that the thermostat is not closing, ...as you already suspect.

I didn't see a comment about what the gauge on the dash is saying about the coolant temp it measures (in the engine water jacket), so maybe you don't have a gauge, just a hi-temp warning light ? If, you have a gauge and it shows the same behavior: noticeable drop in temp when at idle or loafing over the road in OD, this again suggests the thermostat (if there is one) is failing to close down to restrict the flow. Surest diagnostic is just what you think: replace thermostat ...or take it out, put in pot of water heating on the stove and observe behavior as you monitor temperature in the pot.

Other reasons for inadequate heat--besides absent/inoperative/wrong-range thermostat--are restrictions on flow through heater core ...you can get a rough idea of the flow in/out of the heater core by comparing the feel of the in and out hoses (with the heater blower off) ...if in is "hot" and out is "cold" that's the culprit.

Back to you original concern: no worries about transmission temp as long as the radiator (has coolant) and doesn't boil over.