Heater and temp questions (1 Viewer)

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Mar 20, 2020
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Grove, Ok
Hello,

Last night it was 28 degrees out and I drove my 97FZJ for 3 hours round trip. Heater was blowing luke-warm at best. Temps from my Scan Gauge II fluctuated between 175 and 177 degrees during the entire trip. I've searched the forum and see where it could be the control value, heater core plugged and or thermostat. Do those temps sound normal in 28 degree weather and should the heater blow hot at those temps? Also, I will search for information on the control value. While I see recommendations to check it, I don't see any guidance on what I should visually be looking for. Does the 174-177 temp help narrow it down to possibly a thermostat? Any suggestions would help.

Thanks

Robert
 
two other data points that might help diagnose the issue. My floor boards are not wet, I do not smell antifreeze and when I checked my radiator level this morning it was about two cups low.
 
Going to watch my grandson wrestle at regionals today so I will be off line for a bit.
 
Hello,

Last night it was 28 degrees out and I drove my 97FZJ for 3 hours round trip. Heater was blowing luke-warm at best. Temps from my Scan Gauge II fluctuated between 175 and 177 degrees during the entire trip. I've searched the forum and see where it could be the control value, heater core plugged and or thermostat. Do those temps sound normal in 28 degree weather and should the heater blow hot at those temps? Also, I will search for information on the control value. While I see recommendations to check it, I don't see any guidance on what I should visually be looking for. Does the 174-177 temp help narrow it down to possibly a thermostat? Any suggestions would help.

Thanks

Robert

Can only share with you what mine does. (ambient temp higher than yours).

Its seems more than warm enough in my cabin.

Heater temp.jpg
 
Thanks. I’m thinking the thermostat may be stock open. But that goes back to my question is 174 or 177 temp hot enough to generate heat. As a wild card, I also plugged my Scan gauge II in for the first time earlier in the week and routed cable underneath the dash. I don’t think that could impact the heater could it.? Asking because I normally don’t believe in coincidence.
 
Thanks. I’m thinking the thermostat may be stock open. But that goes back to my question is 174 or 177 temp hot enough to generate heat. As a wild card, I also plugged my Scan gauge II in for the first time earlier in the week and routed cable underneath the dash. I don’t think that could impact the heater could it.? Asking because I normally don’t believe in coincidence.
Is the temp reading from the scangauge? I have found them to be accurate. Also, the outside temp is 28F but even forgetting that your temp reading was 174/177 and that is hot enough to provide heat to the trucks system. Is your rear heater putting out warmer air? My guess given the information provided would be a core flush. Let us know what you find.
 
I assume your heater has been working in the recent past. If it hasn't, your troubleshooting flowchart will be much longer, including verifying that the heater core isn't blocked. There's one thing that every Land Cruiser does really well: make heat.

Your scanguage isn't the problem. The heater isn't electrical. The dash control is, see below.

Check the operation of the heater valve on the firewall. You'll need the key on to perform this check, but you do not need the engine running.

You'll need someone to move the temp lever from cold to hot and back while you watch. Most likely, the valve isn't opening fully. You should see about two inches of cable travel, more or less. If you see only about an inch, the valve isn't opening fully. As a temporary fix, you can disconnect the cable and move the valve manually. Do not attempt to move the valve operator (the lever arm) without first disconnecting the cable. You'll damage the opposite end operator and the interior control is electronic.

Your engine temps are OK. The thermostat being stuck open will not be a problem; that condition will only make it warm more slowly. If it's stuck closed, or doesn't open fully, you'll have engine overheating problems.

If your heater valve, on the engine side firewall, is opening and closing fully, your problem is a damper gate malfunction. The complete heater system description, troubleshooting and repair procedures are in the Resources section, as a separate FSM download.
 
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174-177 is a little bit low but not unreasonable, if the t-stat is stuck open itll take longer to get up to operating temp. those temps are more than enough to have heat in the truck. how long did it take to get up to temp while you were driving.

start with checking the heater control valve, or if its looking questionable since the plastic becomes brittle over time it may be worth it to replace it. check the flow through the heater core, if its blocked itll be hot in the inlet side and cooler on the outlet side. if those check out ok it may be a heater control panel issue or a blend door issue
 
FWIW, I have three 80s (currently).
One 1994 which runs at whatever temperature it runs at (I have no idea, but it feels cool when I drive it);
one 1995, which has had no work done to the engine other than replacing hoses and oil seals, which runs between 174° and 178° no matter what I do, no matter what time of year;
another 1995 with a new head, which will not run below 178°, at any time, and typically runs between 178° and 184°, no matter what the weather is outside.
 
Mine does the same exact thing. Blows Luke warm air. I flushed the entire cooling system, checked the valve, blend door and anything else that was suggested. Still blew Luke warm air and cooled the higher I turned the blower up.

Finally one day I turned it all the way to hot then back towards just a skosh and bam hot air. Works about 85% of the time and I assume I need a new hvac controller but haven't confirmed.
 
Here’s some additional datapoints that may help pinpoint the issue. The outside temp today is 54 degrees. I waited until the Scangauge registered 179 and open the hood. The hoses running through the heater valve were hot. Not burning hot but it was close to being uncomfortable when gripped. The hose I’m pointing to in the first pic is only warm. I’m assuming from this the outlet hose in the first pic by being Luke warm signifies blockage in the heater core. Would you agree? I’m also getting about 1.5” inch of travel on the heater valve when moving the interior heat control from side to side. And finally, am I at risk of anything driving the LC while I’m waiting to get time to flush the heater core. The heater is blowing warm but not hot. Thanks

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Your engine isn't in any danger because your heater doesn't work. That circuit is an "extra" cooling circuit; the one your engine needs is up front.

Have you used the troubleshooting matrix in the A/C and Heating section of the FSM?

FWIW, the heater inlet, from the valve should be hotter than the heater outlet; the water has lost heat once it has traveled through the heater core.
 
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When I asked about the scan gauge I was really wondering if feeding the extra cable underneath the dash might have put something in a bind affecting perhaps blend door operation.
 
In my post above I meant this section

 
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