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tito 04-27-2004 03:16 AM

I've been following Janie's post for some info, but have some different questions. It only overheats on the trail. Here are some details

- added an electric pusher fan, but still overheated this weekend on the trail, ended up with what I believe to be vapor lock
- radiator looks new, only a few bits of scale, tubes look open and clear, no leaks
- fan clutch seems to be okay
- hoses are fairly new
- fan is as close to radiator as possible
- running 50/50 coolant to water mix

My questions are:

1)What/where is the best water pump? I'm thinking it may be going south and would prefer a hi-perf unit as replacement.

2) What/where is the best deal on a 4 core radiator and how can I identify what I have? It appears to have a towing package so the radiator should already be beefed up. This is a last resort because of the cost.

I really don't want to have to run the heater while riding at the Invasion.....again.

Thanks for any replies.

TheGossert 04-27-2004 06:28 AM

I love my GMB hi-perf. water pump. It's aluminum and uses bearings instead of bushings.


1BDWAGN 04-27-2004 06:45 AM

Well, I was always told if you overheat at speed it is coolant flow and if the problem occurs at slow speeds it is airflow. Do you have the stock airdam in place? Or a fan shroud? If you have A/C is the condesor packed full of bugs or leaves? Same for radiator. Wouldn't hurt to have a radiator shop see what the temp of your input and output water temps are for the radiator while your truck is running.

mdill 04-27-2004 06:58 AM

Look for the simple things, is there a spring in the
lower hose ?, is the mixture to lean ?
Is timing off ? Do you see good coolent flow when
heated up with the rad cap off ? (Don't be stupid
and burn yourself while trying tying to open the
rad or looking), does you cooling system hold presure ? Start with the basics then work from there.

Mike D.

tito 04-27-2004 08:27 AM

Thanks for the replies, sorry for the delay, I was just able to get back and check the post.

Larry - where can I get a GMB water pump and how $$$? Never heard of those.

1BD - I don't have the air dam, but figured the pusher fan should more than make up for that. I do have a shroud and I pressure sprayed the radiator, A/C compressor and tranny cooler when installing the pusher fan on Sat. Still overheated Sun on the trail.

mdill - Not sure about the hose/spring, that's a good point, DSPO may have put a new hose w/o the spring. If anything, the mixture is too rich - tailpipe black and black smoke when downshifting (auto tranny). The system definitely hold pressure, it was spewing coolant all over the fender well through the overflow tank, but no leaks anywhere else. Although maybe the cap is no good?

Thanks for the ideas. I'll check for the hose spring and get a new cap. Any other ideas are appreciated.

Fornesto 04-27-2004 08:33 AM

There is a company out of San Luis Obispo or Paso Robles, CA that makes high performance water pumps for the AMC. They are very nice, but their name slips me.

Here is is


[ April 27, 2004, 02:34 PM: Message edited by: Fornesto ]

illegalFSJ 04-27-2004 02:12 PM

Could be the thermostat is getting sticky. Cheap enough to throw one in.

tito 04-28-2004 07:34 AM

Thanks for the info, guess I know what I'll be doing this weekend.

zmjeeps 04-29-2004 01:49 AM

If all else fails, an aluminum radiator with an electric puller fan would definately lower your temps.

Rogue 04-29-2004 02:08 AM

spewing coolant all over your fender well sounds like a bad radiator cap, cap increases system pressure, increase system pressure = higher boiling point

FSJ's have what is referred to as a closed system ( i'm talking about thermostat operation here ) a high performance water pump won't necassarily flow more coolant - it definetly won't with a stock thermostat and only will if you have a high flow or no thermostat

a puller fan flows more cfm than a pusher

you say your mechanical fan is as close to the radiator as possible? how is this in relation to the fan shroud? if you don't have one you need one and the fan blades from a side view should see about half of their width out of shroud/ half in, this should alleviate your airflow problems, since it only overheats on the trail it sounds as if airflow is your problem

tito 04-30-2004 01:15 AM


That's the thought I was having - air flow problems. But that's also why I'm confused.

- mechanical fan close to radiator
- fan shroud with fan 1/2 way inside
- electric pusher fan on the front of A/C condensor
- radiator is fairly new, minimal scale buildup
- new thermostat a year ago, 180*

I'd still like to know how to determine how many cores the radiator has, if anyone can give an indentification method it would be appreciated. According to documents I found in the glove box, it came from a dealer in NJ. I don't know if they used diff rads for different areas. But given it seems to have a tow package (tranny cooler, installed Class III hitch), I would think it came with the upgraded rad from the factory regardless of the dealer destination.

The only options that seem likely are the cap, collapsing lower hose and/or failing water pump.

Rogue 04-30-2004 01:58 AM

how many cores or rows it has, hard to put in words, basically how thick it is, you can see the missing cores if its only a 2 or 3 core and then you'll see

Don S has an excellent write-up on airflow specifically for the FSJ, might want to check that out

definetly want to put on that rad cap as it is possible the rad cap is spewing before the thermostat even opens

if you invest in a HI-PO pump make sure to invest in a HI-PO thermostat also

if all that don't fix it - you got problems!!!, seriously though you'll prolly need a bigger radiator

and out of curiousity how how is this thing getting? 240 - 260 is when the head gasket goes, running 200 - 210 would actually be in the "normal" range

kreb 04-30-2004 04:50 AM

napa sells a all new aluminum water pump that is gmb manfucatured. go to their site and they will have the part number.


tito 04-30-2004 07:46 AM

DOH!! Don't say those words - "that's when the head gasket goes"!!

That's my concern, it gets over the 220 mark and probably in the 240 range, but not into the red that I know about. Happens only on the trail and only up long hills. Highway, it runs right at at 180* (just above the blue zone). In stop/go it will get to 210-220 or so with the AC on. When starting, it warms up to 180-190* pretty quick and will stay there all day long if not on a trail or severe stop/go, this tells me the thermostat is working. Correct?

Just wondering if the pump is going and doesn't circulate enough coolant at slow (trail) speeds?

The cap is a definite replacement item. It got over up to about 240 on the trail and that's when the spewing out the overflow tank was happening.

tito 04-30-2004 07:49 AM

PS. Thanks for the info, Kreb. I'll check it out. Don't know that I could justify the Flowkool at $97+, but I thank Fornesto for the link. Hopefully, it won't come to that or a new rad.

Casey 04-30-2004 02:35 PM

A typical water pump only becomes effective above a certain rpm, if you are at a light and you over heat, put the tranny in neutral and give her some gas, while watching the temp gauge. If it goes down quickly the pump is not working well. I have been told that even the high flow water pumps operate the same way, needing some rpm to be effective. So I have always used good re-man.relatively cheap ones.

jgarcia2 05-03-2004 07:41 AM

I know you said you think that the fan clutch is ok, but are you REALLY sure? Mine was doing basically the same thing. I'd drive the freeway at 70 mph and it would be just fine. Then I'd hit the off ramp and get into the, you could watch the needle go up. The trail was the same way.
A friend (and knowledgeable guy) looked at the clutch and said it seemed fine. A couple months later I had it in the hobby shop and asked a guy about the problem. He went over to the fan clutch and said "replace this." He didn't even touch it.
Of course, I bowed before him a couple of times, and then did what he said. He was spot on.

Now, I don't know exactly how he knew, but maybe you could check that closer. Made a helluva difference on my rig.


1BDWAGN 05-03-2004 07:57 AM

FYI, on the waterpump. You can order a Carter from summit for $37.99 which has bearings and ceramic seals and then order the flow kooler conversion disc for AMC waterpumps for $5.95. That is half the cost of the flow kooler pump. Also can get a Robert Shaw high flow thermostat from Stewert Components. Good luck.

tito 05-04-2004 01:46 AM

Thanks for the info on the water pumps and fan clutch.

Took Rogue's advise and bought a new rad cap. The old one had a piece of gasket missing. Question is, was the gasket missing before overheating or torn lose by the overheat pressure/spewing?

I understand the principles of pressure raising the boiling temp. But, why would everything work fine except on long hills on the trail? Going up the hill I can watch the motor get hotter and hotter, then going down the backside of the hill, it's back in "normal" range by the time I get to the bottom. It's like watching at an altimeter in a plane. I go up, the gauge goes up, I descend, the gauge goes down. Driving anywhere else, everything is realitively normal.

I'm also having trouble understanding how this could be caused by an airflow problem. If it's airflow problems, how can it cool down so quick going downhill at the same speed?

Reading through the archives on overheating and one post mentioned the trans fluid could add heat to the radiator, especially on long hills. Anyone have thoughts on this possibility?

I'm wondering if the trans lines are run backwards - through the rad then the cooler. Supposedly the fluid goes through the cooler first, then the rad. The cooler reduces the fluid then the rad makes sure the fluid is close to engine temp, which is desired. Supposedly, this is mostly for winter driving. Anyone know which lines are in/out from the trans or rad? Wondering if the lines got reversed somehow.


Rogue 05-04-2004 05:00 AM

thats a good point about the fan clutch, if you stop when the vehicle is hot and shut if off, the fan clutch should be locked to the water pump or in other words you should not be able to spin, ive seen some people stick a prybar, etc into the fan while the engine is running, works good if it is indeed shot ( you can stop it from spinning ) don't work good if its not shot

now the hill thing......??????????.....that's a good one there

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