LUVTruck.com

I have done a search on Overheating, and thermostats, and gone thru any messages that talked about overheating, but I need some help. I now have an 80 4x4 Mikado, bought it July 26th. I spent the majority of last week going through it trying to make it mechanically stable as my daily driver. On the drive home it overheated about half way back (4.5 hour trip one way), so pulled over let her cool off, found some water, removed the thermostat, (the temp guage wasn't working) got back on the road, turned the heater on, and made it the rest of the way without incident. I took it to a local shop to have it checked because I was thinking the head gasket might be bad due to some smoke and from information I had gotten from another mechanic. The shop did a compression test and tested for foreign substance in the antifreeze, everything checked out ok, temp never got above 170. I managed to track down a new thermostat and got it installed on Thursday, flushed the system in the process. Drove the truck quite a bit Friday and Sat, without any overheating, so thought my problem was solved. Went to work today, it is about 45 miles one way, and after about 30-35 miles, I could smell coolant and saw the signs of overheating again. No, the temp guage still wasn't working, I was at a loss, checked everything I could on that, and still nothing, so was going to order a temp sending unit to see if that was the problem. So I pull over let it cool off (didn't bring any tools, silly me, trusted her to be good), found a place I could get some water, managed to make it to work, a little late, but in one piece. At lunch went and bought a 12mm socket and antifreeze and a ratchet, and after work pulled the thermostat out again. Drove it home, it warmed up, (did I forget to mention that after it overheated on my way to work, the temp guage started to work) according to the temp guage it got up to about 3/4 to the H mark, maybe a little higher after about 30 miles or so. I pulled off checked the levels, didn't lose any coolant and let it cool down for about 15 mins and made it home without spewing coolant. The strange thing was that after I got off the highway and was cruising at 45mph, it cooled down even more, almost to the normal operating mark. So I'm stumped, I drove it probably 60-70 miles (highway miles 55-60mph) both Fri and Sat and never had a problem, but for some reason today, same speeds it had a problem.

Ok, I'm ready, let me hear your thoughts. Any thing would be helpful for me to look at. I'm thinking about taking it back to the shop and have it tested again and the head gasket checked. If I left anything out, ask and I will try to fill it in, I tried to give as much information as necessary without adding irrelevent information.

Thanks in advance,
Chad

P.S. I've got quite a few pics so far, and will get them up soon. She certainly wasn't pretty when I got her, but I am making improvements slowly. Mechanical 1st, then cosmetics.

I think that the problem may be that the radiator is partially clogged up. At moderate speeds the cooling system can handle scrubbing away the heat but at hwy speeds, the coolant isn't flowing enough to take care of the problem. Some of the surface area of the core isn't getting hot with coolant. If the thermostat is good and the water pump works, it should be just fine. There is the outside chance that it's something minor like a loose fan belt but you could notice that right off by the belt sqwealing. Air temp has a lot to do with it too.
Go back to the basics, first test the thermostat by placing it in a pan of boiling water, if it opens, it's good. Then check the flow thru the radiator. Cover the lower radiator hose outlet with your hand and fill the radiator with water. Then remove your hand and watch the flow draining out. It should flow fast and steady and then quit all of a sudden once it's empty. If the flow steps down towards the end to a smaller rate of flow, this is an indication that the core is plugged up.
If you are working items to get the truck more mechanicly sound, the radiator must be in need of an overhaul too. It's a very common problem is often overlooked.

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Previous setup: 4.1 Buick V-6/TH 350
Current setup: 400 Small Block Chevy V-8/TH 350
9" ford rear end/short bed/blue
What do Water, Electricity and Humans have in common... They all travel the path of least resistance.

when replaced my head a year ago the vacuum diagram under the hood was wrong(?)and i hooked the vac advance up wrong and it really over heated when the secondary bore was open.

the diagram said i needed to hook up the advance to a tee that split off to the charcoal can. i had ever seen this but i did it the way the diagram said. problem didn't stop untill i hooked it up to straight manifold vac like every other vehicle i've ever owned.

after that it stoped over heating.

do yourself a favor though and get a new radiator cap(i stress the new radiator cap),and go through the vacuum crap very carefully and make sure that the timing and points are good and set properly.

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my father in law lost two engines out of the same car before he checked the radiator cap and saw it was cracked. Now it's the first thing he suggests lookin' at when you have heat problems.

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Richard Barnes Salt Lake, Utah
1980 Luv Mikado 4X4
http://geocities.com/luvtruck2004/

And if you find the radiator core needs to be rodded out, consider replacing the core with a 3 row core instead of using the 2 row core you probably now have.

wish i had done that.........is there one available? the right size and all,ya know.

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Blue -- Thanks for the advice, tested the thermostat, all was good there, (it was brand new so I hoped that wasn't it), then tested the flow from the radiator, and it slowed as the water was coming out so if the diagnosis is good, looks like I get to take it to a radiator shop tomorrow. Not that I doubt you, I just know nothing about radiators, and what you say sounds plausible.

All the luv -- Thanks to you also, checked over all of the lines, all seemed to be functioning and hooked up in the right places.

Narc -- The radiator cap looks good, but I will probably change it out just to make sure.

Robert -- That is a good idea, I spose it will depend on the $$$ difference. Will check on that tomorrow.

Just out of curiosity, because I don't have any books yet, (bought a couple on ebay, waiting for them to arrive) what is the capacity of the Radiator and cooling system? When I drained it tonight to check this other stuff, I refilled it but it didn't even take a gallon of liquid. Seemed a little off.

Thanks to all for looking and passing along some thoughts. And thank you to all of you that sent me telepathic thoughts and ideas as well.

Chad

1.6 gallons in my book

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1980 luv sport 4x4 Just a memory now
Frame rusted from the inside. Truck stripped and now looking for a new donor in southern ohio

I have the radiator out of mine, that I am not using now due to runnin a v8, Never had any kind of over heating trouble. $20 plus shippin and its yours.

Yup, sounds just like what my blue one was doing till a few weeks ago and after replacing everything else over last 2 yrs i finally replaced radiator and viola....problemo el solvo!!!
Chad, as I said buddy that ol thing sat since 95, and i drove it around town here and never noticed anything wrong but then i never went far either. That temp sensor wire on that truck was unplugged when i got it. I had it working but the connection seemed a little loose,I dont think thats a big deal but i do believe ya need a radiator by what yer saying here. And Oh yeah before I forget......am going out to south 40 and try to hunt down some emblems fer ya tomorrow.

Luvinit -- PM sent.

Chad

Thanks blue, I'll be looking for them.

Chad

Looks like it is fixed. Had the radiator fixed yesterday, it was plugged, no overheating today. Thanks to everyone for the help.

Chad

wheew!!!! Now i feel alot better to hear that cause i want you to be happy with it.